MOCKS 1
NAME ______________________________________ INDEX NO _____________________
DATE ____________________________ SIGN ______________________________
233/1
CHEMISTRY
PAPER 1
TIME 2HRS
- Element K has atomic number 20 while element M has atomic number 8.
- Write the electron configuration of K and M
K ______________________ (1mk)
M ______________________ (1mk)
- Write the symbol of the most stable ion of K and M
K ____________________________ (1/2 mk)
M ___________________________ (1/2mk)
- Molten lead (ii) iodide is electrolyzed using inert electrodes. Write the half equation of the reactions that occur at the anode and cathode.
- Anode _______________________________________ (1mk)
- Cathode ______________________________________ (1mk)
- b) Explain why the conductivity of metals decrease with increase in temperature
________________________________________________________________________
________________________________________________________________________
- Some sodium chloride was found to be contaminated with copper (ii) oxide. Describe how a sample of dry sodium chloride can be obtained from the mixline
________________________________________________________________________
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- Hot platinum wire was lowered into a flask containing concentrated ammonia solution as shown below
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State and explain the observations made (3mks)
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- a) What is a dative boud? (1mk)
________________________________________________________________________
- b) Draw a dot (.) and cross (x) diagram to show bouding in carbon (ii) oxide (2mks)
- Air was passed through several reagents as shown in the flow chart diagram
- What is the purpose of concentrated potassium hydroxide solution? (1mk)
________________________________________________________________________
- Write an equation for the reaction which takes place in the chamber with magnesium powder (1mk)
________________________________________________________________________
- Name one gas which escapes from the chamber containing magnesium powder (1mk)
________________________________________________________________________
- Name the following substances
- CH2CH CH2CH3 ______________________________________ (1mk)
- CH3CHCHCH2CH3 _______________________________________ (1mk)
- State the observation made when compound in (a) above was passed through acidified potassium (vii) manganite (1mk)
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- The diagram below shows a wooden splint that was placed horizontally across the middle part of a non-luminous flame.
- Explain the observation made (2mks)
_____________________________________________________________________
________________________________________________________________________
- Explain why non-luminous flame is preferred for heating than luminous flame (1mk)
_____________________________________________________________________
________________________________________________________________________
- Explain giving reasons why?
- Sulphuric(vi) acide is not used with marble in the preparation of carbon(iv) oxide (2mks)
_____________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- Water cannot be used to extinguish oil fire
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- 15cm3of a solution containg 2.88g/dm3 of an alkali XOH completely reacts with 20.0cm3 of 0.045m sulphuric(vi) acid. Calculate the molarity and relative atomic mass of x present in the alkali
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- An hydrocarbon Q was found to decolourise potassium manganate(vii)solution. When two moles of Q were burnt completely six moles of carbon(iv)oxide and six moles of water were formed.
- Write the structural formula of Q (2mks)
________________________________________________________________________
________________________________________________________________________
- Name the homologous series to which Q belongs
________________________________________________________________________
________________________________________________________________________
- The diagram below represents an electrochemical cell
- i) On the diagram label the salt bridge (1mk)
- ii) State two observations made in cell B (1mk)
________________________________________________________________________
________________________________________________________________________
- Write the overall ionic equation of the cell (1mk)
________________________________________________________________________
________________________________________________________________________
- During the extraction of copper and zinc from their ores, some of the processes include
- Crushing
- Mixing of the crushed ore with oil and water and bubbling air through it.
- (i) Name the process (ii) above (1mk)
________________________________________________________________________
(ii) What is the purpose of (ii) above
________________________________________________________________________
________________________________________________________________________
- Dry chlorine gas was passed through two pieces of coloured cotton cloth as shown
- State what is observed in each experiment (1mk)
Experiment I
______________________________________________________________________
Experiment II
______________________________________________________________________
- Explain your observation using an equation (1mk)
______________________________________________________________________
______________________________________________________________________
- a) what is meant by solubility? (1mk)
________________________________________________________________________
________________________________________________________________________
- b) In an experiment to determine the solubility of solid Y in water at 30oC the following results were obtained.
Mass of evaporating dish = 26.2g
Mass of evaporating dish + saturated solution = 42.4g
Mass of evaporating dish + dry solid y = 30.4g
Using the information, determine the solubility of solid Y at 30oc in grams per 100g of water (2mks)
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- the molar heat of formation of carbon(ii) oxide is –105kjmol-1, molar heat of combustion of carbon is -393 kjmol-1
by using an energy cycle diagram, determine the molar heat of combustion of carbon(ii)oxide (3mks)
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- The diagram below was used to study the effect of heat on copper(ii)sulphate crystals
- Name liquid M (1mk)
_____________________________________________________________________
- State and explain the precaution that should be made before stopping heating (2mks)
_____________________________________________________________________
_____________________________________________________________________
_____________________________________________________________________
- Deuterium 21D and tritium 31T are two isotopers of hydrogen. They react to form element Y and neutron particles according to the equation below.
21D + 31T abY + 10n
- Find the value of a and b (2mks)
________________________________________________________________________
________________________________________________________________________
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- What name is given to the type of reaction undergone by the isotope of hydrogen (1mk)
________________________________________________________________________
- A gas occupies 4dm3 at -230c and 152mmHg. At what pressure will its volume be halved, if the temperature then is 2270c? (2mks)
________________________________________________________________________
________________________________________________________________________
________________________________________________________________________
- Ammonium nitrate was gently heated and the products collected as shown in the diagram
- Identify
- Colourless liquid H (1mk)
____________________________________________________
- Gas G (1mk)
- Describe one chemical test that can be used to identify gas G
_____________________________________________________________________
_____________________________________________________________________
- The diagram below shows the acidic and basic oxides fit into the general family of oxide
- State the type of oxide that would be placed in the shaded area (1mk)
_____________________________________________________________________
- Name an oxide that would be placed in the shaded area (1mk)
_____________________________________________________________________
- A dynamic equilibrium between dichromate and chromate ions is established as shown in the equation below.
Cr2O72-(aq) + ZOH–(aq) 2Cro2-4 + H2O (l)
Orange Yellow
- What is meant by dynamic equilibrium? (1mk)
_____________________________________________________________________
_____________________________________________________________________
- State and explain the observation made if a dilute hydrochloric acid is added to the equilibrium mixture (2mks)
_____________________________________________________________________
_____________________________________________________________________
- An experiment showed that the composition of a compound to be 5838% Barium, 13.72% Sulphur and 27.47% oxygen. Calculate the empirical formula of the compound (Ba = 137; S=32, O=16) (3mks)
________________________________________________________________________
________________________________________________________________________
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- In an experiment to study diffusion of gases, the following set up was used
- State and explain observations made in the experiment (2mks)
________________________________________________________________________
________________________________________________________________________
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- Write an equation for the reaction that occurs in the experiment (1mks)
__________________________________________________________________
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- The figure below is an energy level diagram for the reaction 2Z (g) + 2B(g) = 2AB(g)
Explain the effect of yield AB by
- Increase in pressure (1 ½ mk)
_____________________________________________________________________
_____________________________________________________________________
- Decrease in temperaline (1 ½ mk)
_____________________________________________________________________
_____________________________________________________________________
- Study the following changes that took place when the following substances are exposed to air.
- NaOH(s) I NaOH(aq)
- N2CO3.IOH2O(s) II Na2CO3(s) + IOH2O(l)
- CuSO4(s) + 5H2O(l) III CuSO4.5H2O(s)
Name the process (3mks)
I _______________________________
II ______________________________
III _____________________________
- A white solid K was heated. It produced a brown gas A and another gas B which relights a glowing splint. The residue left was yellow when hot and white when cold.
- Identify gases A and B (2mks)
A ______________________________
B ______________________________
- Write an equation for the decomposition of solid K (1mk)
_____________________________________________________________________
_____________________________________________________________________
- Bronze is an alloy of copper and another metal. Identify the other metal.
_______________________________________________________________________
_______________________________________________________________________
MOCKS 1 2023
NAME…………………………..………………DATE ………………………………………
INDEX NO.……….……….………………………..… SIGNATURE ……………..………
233/2
CHEMISTRY
(THEORY)
PAPER 2
THEORY
- The grid below shows part of the periodic table. Study it and answer the questions that follow. The letters do not represent the true symbols of the elements.
A | ||||||||
I | B | C | D | E | ||||
F | G | H | ||||||
- Which element forms an ion of charge – 2? Explain your answer 2marks
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
(b) What is the nature of the oxide formed by element C? 1mark
………………………………………………………………………………………………………………
- How does the reactivity of H compare with that of E? Explain. 2marks
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Write the chemical equation for the reaction between B and chlorine? 1mark
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Explain how the atomic radii of the following compare; 2marks
- F and G
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- B and G
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- The oxides of B and D are separately dissolved in water. State the effect of each product on litmus paper. 2marks
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- 20cm3 of a solution of a hydroxide of I completely neutralizes 17.5cm3 of 0.5M sulphuric (VI) acid. Calculate the concentration in moles/litre of solution of the hydroxide of I3marks
- a) Sulphur occurs naturally in two different forms called allotropes;
- What are allotropes? 1mark
………………………………………………………………………………………………………………
- The two allotropes of sulphur are stable at different temperatures, as shown in the equation below.
Above 95.50C
Rhombic sulphur Monoclinic sulphur
Below 95.50C
Give a name to the temperature 95.50C 1mark
…………………………………………………………………………………………………
- b) Below is a flow chart diagram for the contact process for the manufacture of sulphuric (VI) acid.
- Give the name of chambers labeled 1 ½ mark
X
………………………………………………………………
Y
………………………………………………………………
Z
……………………………………………………………….
- State the three conditions in the converter. 1 ½ mark
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Explain why gases are passed through ; 2marks
I – The dust precipitator and drying power
…………………………………………………………………………………………………………………………………………………………………………………………………….
- II- The chamber labeled YWrite the balanced equations for the reactions in;3marks
Step 2:
………………………………………………………………………………………………….
Step 3:
………………………………………………………………………………………………….
Step 4:
………………………………………………………………………………………………….
- Calculate the volume of sulphur (VI) oxide gas in litres that would be required to produce 178kg of Oleum in step 3. (Molar gas volume at s.t.p.=22.4l, H=1, O=16, S=32)3marks
……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Below is a scheme of some reactions of propanol. Study it and answer the questions that follow.
- State the reagents and conditions required to effect step I 3marks
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Draw the structural formulae and name product Z. 1mark
…………………………………………………………………………………………………………………………………………………………………………………………………….
- Name product Q 1mark
………………………………………………………………………………………………………………
- Explain how product Y can be distinguished from the product formed after step I has taken place. 2marks
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- What name is given to the process in Step II and step III 2marks
Step II
………………………………………………………………………………………………………………………………………………………………………………………………………………
Step III
………………………………………………………………………………………………………………………………………………………………………………………………………….
- (i) Define the term hydrocarbon 1mark
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
(ii) Draw the structure of 1, 2 – dibromopropane 1mark
4.
- What is the molar heat of combustion of a substance? (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- The experiment below was set up to determine the molar heat of combustion of methanol.
The following data was obtained from the above experiment.
Mass of burner + methanol before burning = 62.74g
Mass of burner + methanol after burning = 62.36gFinal temperature of water = 38.50C
Initial temperature of water = 23.50C
Volume of water used = 100cm3
- From the above results work out the molar heat of combustion of methanol. (3marks)
(Density of water =1g/cm3, C = 12, O=16, H= 1.0)
Specific heat capacity of solution 4.2Kj K-1g K-1)
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Write a thermo chemical equation for this reaction. (1mark)
…………………………………………………………………………………………………………………………………………………………………………………………………………………..
- Explain why the value obtained in (i) above may be lower than the actual value. (1mark)
…………………………………………………………………………………………………………………………………………………………………………………………………………………….
- Study the data given below
C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l) ΔH = – 2209 KJmol-1
H2(g) + ½ O2(g) H2O(l) ΔH = -286KJmol-1
C(s) + O2(g) CO2(g) ΔH = -406KJmol-1
Use this information to find the heat of formation of propane. (3marks)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- What do you understand by the term heating value of a given fuel? (1mark)
……………………………………………………………………………………………………………………………………………………………………………………………………………….
……………………………………………………………………………………………………………………………………
- State two factors you consider when choosing a fuel. (1mark)
…………………………………………………………………………………………………
5.
- Magnesium ribbon was reacted with steam as shown in the diagram below.
- State two observations in the boiling tube. (2marks)
……………………………………………………………………………………………………………………………………………………………………………………………………….………………………….
- Describe how you test for gas x (2marks)
……………………………………………………………………………………………………………………………………………………………………………………………………………..…………………….
- State one industrial use of the product formed in the boiling tube at the end of the experiment. (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………..
-
- Explain what is meant by the term neutralisation. (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Starting with 50cm3 of 2M nitric (v) acid, describe how you would prepare crystals of sodium nitrate. (3marks)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..………………
- Complete the table below. (1mark)
Indicator | Colour in | |
Acidic solution | Alkaline solution | |
Phenolphthalein | __________ | Pink |
Methyl Orange | Pink | __________ |
- When magnesium is burnt in air two reactions take place forming two different compounds. Write down the equations for the two reactions. (2marks )
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- The set up below is used to measure the change in mass during the course of the reaction between dilute hydrochloric acid (Excess) and marble chips at 220C.
Changes in mass were noted at one minute intervals and were as follows;
Time (Min) | 1 | 2 | 3 | 4 | 5 | 6 | 7 |
Loss in mass (g) | 0.26 | 0.46 | 0.60 | 0.69 | 0.73 | 0.73 | 0.73 |
- Write an equation for the reaction taking place in the flask. (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………..…
- Give a reason why the mass of the flask charged with time? (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………..
- What is the role of cotton wool at the mouth of the flask? (1mark)
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Explain why it is not advisable to use dilute sulphuric (VI) acid with marble chips in this experiment (1mark)
…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Plot a graph of loss in mass (vertical axis) against time. Label the curve 220C (3marks)
- On the same axis in (e) above sketch the graph you would expect to obtain if the experiment was repeated at 350 Label the curve 350C. (1mark)
- State what would happen if the marble chips were replaced with the same mass of marble powder. Explain your answer. (1mark)
………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- Determine the volume of carbon (IV) oxide produced if 0.12g of marble chips was reacted with excess dilute hydrochloric acid. (Experiment done at room temperature and pressure. Molar gas volume at r.t.p = 24dm3,Ca = 40.0,O = 16, C = 12.0) (2marks)
……………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………
- In an experiment ,0.71g of hydrated sodium carbonate (Na2CO3.XH2O) was treated with dilute nitric v acid and the gas evolved was carbon iv oxide which was measured using a syringe at stp.The volume of carbon iv oxide obtained was 56cm3
a.Write the equation for the reaction between anhydrous sodium carbonate and dilute nitric v acid (1mk)
- Calculate the number of moles of carbon iv oxide gas collected at s.t.p (molar gas volume at stp=22,400) (2mks)
c.Calculate the mass of anhydrous sodium carbonate reacted (3mks)
d.Calculate the mass of water in 0.715g of hydrated sodium carbonate (1mk)
- Determine the R.F.M of hydrated sodium carbonate, hence the value of X(3mks)
MOCKS 1 2023
Name _________________________________________ Index No. _____________________________
Candidate’s Signature ___________________
Date _________________________________
233/3
CHEMISTRY
PAPER 3
PRACTICAL
2 ¼ HOURS
INSTRUCTIONS TO CANDIDATES
- Write your name and admission number in the spaces provided.
- Sign and write the date of examination in the spaces provided above.
- Answer all questions in the spaces provided.
- KNEC Mathematical tables and silent non-programmable electronic calculators may be used.
- All working must be clearly shown where necessary.
- Candidates should answer all the questions in English.
FOR EXAMINER’SUSE ONLY
Question | Maximum Score | Candidate’s Score |
1 | 19 | |
2 | 10 | |
3 | 11 | |
TOTAL SCORE | 40 |
This paper consists of 8 printed pages
Turn Over
- You are provided with:
– Solution A, a mixture of two bases sodium hydroxide and sodium carbonate solids
dissolved in a 1 litre solution.
– Solution B, 0.2M hydrochloric acid.
– Phenolphthalein and methylorange indicators.
– Solution C, barium chloride solution.
You are required to determine the concentration of each of the reactants in the mixture.
Procedure 1
Pipette 25.0cm3 of solution A into a conical flask.
Add two drops of methylorange indicator.
Titrate solution A with B until the yellow colour just changes to pink.
Record your results in the table below.
Repeat the procedure to obtain two more readings.
Table I (3 marks )
1 | 2 | 3 | |
Final burette reading (cm3) | |||
Initial burette reading (cm3) | |||
Volume of solution B used (cm3) |
(a) Calculate the average volume (V1) of solution B used. (1 mark )
(b) Calculate the number of moles of hydrochloric acid that reacted. (1 ½ marks )
Procedure II
Pipette 25.0cm3 of solution A into a conical flask. Measure 15.0cm3 of barium chloride
solution (solution C) with clean measuring cylinder.
Add it to the solution A in the conical flask. Shake it gently and add three drops of phenolphthalein indicator.
Titrate solution B into the conical flask until the pink colour just changes to colourless.
NB: The white precipitate should remain in the flask.
Repeat the procedure to obtain two more readings.
Table II ( 3 marks )
1 | 2 | 3 | |
Final burette readings (cm3 | |||
Initial burette reading (cm3) | |||
Volume of solution B used (cm3) |
(c ) Calculate the average volume (V2) of solution B used. (1 mark )
(d) The equation for the formation of white precipitate
Na2CO3 (aq) + BaCl2 (aq) BaCO3 (s) + 2NaCl (aq)
During titration II the white precipitate formed after adding barium chloride does
not take part in the titration but all the hydroxide ions (OH–) in the solution are neutralized.
(i) Calculate the moles of the acid (solution B) reacting in titration II. ( 1 ½ marks )
(ii) Calculate moles of sodium hydroxide (OH–) reacting during the titration. ( 1 ½ marks )
(e) Calculate number of moles of acid that reacted with sodium carbonate in the mixture. ( 1 ½ marks )
(f) Calculate the concentration of solution A in terms of sodium hydroxide in
moles per litre. ( 1 ½ marks )
(g) Write an ionic equation for the reaction of the acid with sodium carbonate. ( 1 mark)
(h) (i) Calculate the number of moles of sodium carbonate in the mixture. (1 mark )
(ii) Calculate concentration of solution A in terms of sodium carbonate in
moles per litre. (1 ½ marks )
- You are provided with solid Z. Carry out the tests below and write your observations
and inferences.
(a) Using a clean metallic spatula, heat a half of solid Z in a Bunsen burner flame.
Observation | Inferences |
( 1 ½ marks ) |
( 1 marks |
(b) Dissolve the remaining portion of solid Z into 10cm3 of distilled water in a boiling tube.
Divide the resulting solution into four portions.
Observation | Inferences |
( 1 mark ) |
( ½ mark ) |
(c ) To 1st portion, add 3 drops of acidified potassium manganate (VII)
Observation | Inferences |
( ½ mark ) |
( 1 ½ marks ) |
(d) To the 2nd portion, add 3 drops of acidified potassium dichromate (VI) and warm.
Observation | Inferences |
( ½ mark ) |
( 1 ½ marks ) |
(e) To the 3rd portion, add all the NaHCO3 provided.
Observation | Inferences |
( 1 mark ) |
( ½ mark ) |
(f) To the 4th portion, add 3 drops of universal indicator and determine the pH value.
Observation | Inferences |
( 1mark ) |
( ½ mark ) |
- You are provided with solid Y. Carry out the tests below and record your observations and
inferences in the spaces provided.
(a) Place half of solid Y in a boiling tube and heat. Test any gas produced with litmus paper.
Observation | Inferences |
( 1 ½ marks ) |
( 1 mark ) |
(b) Place the remaining solid Y into a boiling tube. Add about 10cm3 distilled water and
shake. Divide the resulting solution into 5 portions.
Observation | Inferences |
( ½ mark ) |
( ½ mark ) |
(c ) To the 1st portion, add NaOH(aq)dropwise till in excess.
Observation | Inferences |
( 1mark ) |
( ½ mark ) |
(d) To the 2nd portion, add NH3 (aq) dropwise till in excess.
Observation | Inferences |
( 1 mark ) |
( ½ mark ) |
(e) To the 3rd portion, add 1cm3 of acidified hydrogen peroxide followed by
NaOH(aq) dropwise till in excess.
Observation | Inferences |
( 1 mark ) |
( ½ mark ) |
(f) To the 4th portion, add 3 drops of lead (II) nitrate and then filter.
Observation | Inferences |
( 1 mark ) |
( 1 mark ) |
(g) To the 5th portion, add 3 drops of acidified barium nitrate solution.
Observation | Inferences |
( ½ mark ) |
( ½ mark ) |
MOCKS 1 2023
233/3
CHEMISTRY
PAPER 3
PRACTICAL
021
Kenya Certificate of Secondary Education
CHEMISTRY
PAPER 3
CONFIDENTIAL TO SCHOOLS
The information contained in this paper is to enable the head of Institution and the teacher in charge of Chemistry to make adequate preparations for the Form 4 entrance examination. NO ONE ELSE should have access to this paper or acquire knowledge of its contents. The teacher in charge of Chemistry should NOT perform any of the experiments in the same room as the candidates NOR make the results of the experiments available to the candidates or given any other information related to the experiments to the candidates. Doing so will constitute an examination irregularity which is punishable.
In addition to the apparatus and fittings found in a Chemistry Laboratory, each candidate will require the following:
- 1g solid Y
- 1g solid Z
- Metallic spatula
- 6 test tubes in a rack
- 2 boiling tubes
- Test tube holder
- Filter funnel
- Filter paper (one)
- Distilled water
- Acidified potassium manganate (VII) + dropper
- Acidified potassium dichromate (VI) + dropper.
- About 1g of NaHCO3 (s)
- pH chart
- Universal indicator.
- 2M NaOH(aq) + dropper
- 2M NH3 (aq) + dropper.
- Blue and red litmus papers.
- Acidified hydrogen peroxide + dropper.
- Measuring cylinder (10 mls ).
- Acidified 2M Barium Nitrate + dropper
- 2M Lead (II) nitrate + dropper.
- Bunsen Burner.
- 150cm3 of solution A.
- 150cm3 of solution B
- 50cm3 of solution C
- 25.0cm3 pipette.
- 50.0cm3 burette.
- A clamp and stand.
- 100ml measuring cylinder.
- 3 conical flasks.
- White tile.
- Phenolphthalein indicator.
- Methyl orange indicator.
NOTE:
-
- Solution A is prepared by dissolving a mixture of 8g sodium hydroxide and 10.6g sodium carbonate in distilled water to make 1 litre solution.
- Solution B is prepared by measuring 17.2cm3 of concentrated hydrochloric acid ( specific gravity 1.18) to 500cm3 of distilled water and then making it to one litre.
- Solution C 0.1M barium chloride solution.
- Solid Y – Hydrated ammonium iron (II) sulphate
- Solid Z – Maleic acid
MOCKS 1 2023
MARKING SCHEME
233/2
CHEMISTRY
PAPER 2
JULY/AUGUST
Question 1
- A (√1mk) elements in group (vi) have 6 electrons in the outermost energy level, they react by gaining 2 electrons.√1mk
- Amphoteric Oxide √1mk
- Element E is more reactive than H (√1mk) Elements E and H are non – metals in group (VII) and reactivity decreases down the group √1mk / E is smaller than H and hence has a higher electron affinity therefore more reactive.
- B(s) + Cl2(g) BCl2(s) 1mk
- (i) The atomic radius of element F is greater than that of G √1mk / Across period number of protons (nuclear charge increases increasing effective nuclear charge.
(ii) The atomic radius of element G is greater than that of B. √1mk
- Solution of oxide of B changes red litmus paper blue and has no effect on blue litmus paper 1mk while solution of oxide of D changes blue litmus paper red and has no effect on red litmus paper. 1mk
- 2IOH (aq) + H2SO4 (aq) I2SO4(aq) + 2H2O(l) √1mk
2 : 1
Moles of H2SO4 17.5 x0.5 = 0.00875moles √½ mk
1000
Moles of IOH 0.00875 ÷ 2 = 0.004375 moles √½ mk
Molarity of IOH = 1,000 x 0.004375
20
= 0.21875M √1mk
Concentration = 0.21875 moles/litre √½ mk
Question 2
- (i) Crystalline forms of sulphur √1mk
Or
Existence of sulphur in more than one form in the same physical state.√1mk
(ii) Transition temperature √1mk
- (i) X – dilution chamber √1 ½ mk
Y- Heat exchanger √1 ½ mk
Z – Burner √1 ½ mk
(ii) Vandalism (v) catalyst √1 ½ mk
Temperature – 5000C √1 ½ mk
Pressure – 200atm √1 ½ mk
- I – To remove dust particles and water vapour that could otherwise poison the catalyst √1mk
II- Lose heat and pre-heat incoming gases √1mk
- Step 2; 2SO2(g) + O2(g) 2SO3(g) √1mk
Step 3: SO3(g) + H2SO4(l) H2S2O7 (l) √1mk
Step 4: H2S2O7(l) + H2O(l) 2 H2SO4(l) √1mk
- H2SO4(l) + SO3(g) H2S2O7(l) √½ mk
1 : 1 : 1
1 mole of oleum = 178,000 = 1,000moles
178
1 mole at s.t.p = 22.4L
1,000moles = ? √½ mk
= 1000 x 22.4 = 22,400 litres √1mk
Question 3
- Reagent : Hydrogen gas √1mk
Conditions: – Nickel catalyst √1mk
– I50-2500C (temperature) √1mk
- H H H
H C C C H
Br H H
I – Bromopropane √1mk
- Polypropene √1mk
- Y decolourisesbromine water √1mk while the product formed after step I has taken place does not √1mk
- Step II – dehydration √1mk
Step III – substitution √1mk
- (i) A hydrocarbon is a compound that contains carbon and hydrogen only √1mk
(ii) H H H
H C C C H
Br Br H √1mk
Question 4
- Molar heat of combustion is the enthalpy change that occurs when one mole of a substance is burnt completely in oxygen. √ 1 mk
-
- Mass of methanol = 0.38g √ ½ mk
Change in temp. ΔT = 38.5 – 23.5
= 150C
Heat produced. = MCDT
= 100 x 4.2 x 15 √ ½ mk
1000
= 63.1KJ.
Molar mass of ethanol (CH3OH) = 32 √ ½ mk
Molar heat of combustion = 63.1 x 32 √ ½ mk
0.38
= 5313.68 KJ mol-1
- CH3OH(l) + H2O2(g) CO2(g)+ 2H2O(l) √ 1 mk ΔH = -5313.68KJmol-1
- Heat is lost to the environment
Hence the value is lower √ 1 mk
- Equation for formation of propane.
3C(s) + 4H2(g) C3H8(g) √ 1 mk
Heat of formation = 3 (-406) + 4 (-286) + 2209) √ 1 mk
= -1218 – 4576
= – 3585 KJmol-1 √ 1 mk
- This is the amount of heat energy given out when a unit mass or unit volume of fuel is completely burned in oxygen. √ 1 mk
- Heating value
- Ease and rate of combustion
- Availability
- Ease of transportation any 2 correct ½ mk each
- Ease of storage
- Environmental effects
- Cost
Question 5
-
- Magnesium burns with a bright white flame √ 1 mk
A white solid is formed √ 1 mk
- Place a burning splint √ 1 mk near the mouth of the test tube containing the gas.
A ‘pop’ sound is produced.
This confirms that the gas is hydrogen √ ½ mk
- Making lining of furnaces. √ 1 mk
-
- This the reaction between a givennumber of moles of hydrogen ions (H+)√ 1 mk and an equal number of hydroxide (OH–) ions to form water.
- Add 50cm3 of 2M√ 1 mk sodium hydroxide solution.
- Evaporate √ ½ mk the mixture to obtain a saturated solution.
- Leave the saturated solution for some time to √ ½ mk
- Filter the crystals and dry then dry then√ ½ mk between two filter papers.
Indicator | Colour in | |
Acidic solution | Alkaline solution | |
Phenolphthalein | Colourless √ ½ mk | |
Methyl Orange | Yellow √ ½ mk |
- 2Mg(s) + O2(g) 2MgO(s) √ 1 mk
3Mg(s) + N2(g) Mg3N2(s) √ 1 mk
Question 6
- CaCO3(s) + 2HCl(aq) CaCl2(aq) + H2O(l) + Co2(g) √ 1 mk
- The carbon (iv) oxide formed escaped into the atmosphere. √ 1 mk
- To prevent acid from spraying out. √ 1 mk
- Forms insoluble salt √ ½ mk of calcium sulphate which forms a coat √ ½ mk on the surface of the marble chips preventing any further reaction. √ 1 mk
- The reactions rate would increase √ ½ mk marble powder provides a larger surface area, more particles are involved in reactions, thus increasing the rate of reaction. √ ½ mk
- CaCo3(s) + 2HCl+(aq) CaCl2(aq) + H2O(l) + CO2(g) √ ½ mk
1mole 2moles 1mole
0.12g 0.12 x 24dm3√ 1 mk
100
= 0.0288dm3 √ ½ mk
Question 7
7(a) Na2CO3(s) + 2HNO3(aq) 2NaNO3(aq) + CO2(g) +H2O(l)
(b) 1 mole of CO2(g) 22400cm3
56cm3
=0.0025 moles
(c) Mole ratio Na2CO3 : CO2
1 : 1
? 0.0025moles
0.0025moles of Na2CO3
1Mole of Na2CO3= 106g
0.0025moles = ?
= = 0.265g
(d) Mass of water= 0.715-0.265=0.45g
(e)
Na2CO3 | H2O | |
Mass | 0.265g | 0.45g |
RFM | 106 | 18 |
Moles | 0.265/106=0.0025 | 0.45/18=0.025 |
Mole ratio | 0.0025/0.0025=1 | 0.025/0.0025=10 |
X=10
233/3
CHEMISTRY
PAPER 3
PRACTICAL
021
Kenya Certificate of Secondary Education
CHEMISTRY
PAPER 3
MOCKS 1 2023
MARKING SCHEME
- Procedure I
Table 1
1 | 2 | 3 | |
Final burette reading | 25.1 | 35.0 | 39.9 |
Initial burette reading | 0.0 | 10.0 | 15.0 |
Volume of solution B used | 25.1 | 25.0 | 24.9 |
( Compare / use the teacher’s value )
Award marks as follows:
A: Complete table ( 1 mark )
Conditions
Complete table with three titration 1 mark
Incomplete table with two titrations ½ ark
Incomplete table with one titration 0 mark
B: Decimal place ( 1 mark)
Conditions :
Accept only one or two decimal places used consistently.
If two decimal place the 2nd decimal place MUST be either o or 0.5
C : Accuracy 1 mark
Compare the student’s titre value with teacherstitre values.
Conditions
At least within ± 0.1 1 mark
At least within ± 0.2 ½ mark
Above ± 0.2 0 mark
D: Principles of averaging 1 mark
Values averaged must be shown and within ± 0.1 of each other
- (a) 25.1 + 25.0 + 24.9 Ö ½
3
= 25.0cm3Ö ½
(b) Moles of acid that reacted
If 1000cm3 0.2 moles
Then 25cm3 25.0 x 0.2 Ö1
1000
= 0.005 moles Ö ½
Procedure II
Table II
Award according to procedure I table I
1 | 2 | 3 | |
Final burette reading | 12.6 | 25.1 | 37.6 |
Initial burette reading | 0.0 | 12.6 | 25.1 |
Volume of solution B used | 12.6 | 12.5 | 12.5 |
( Compare / use the teacher’s value )
(c ) 12.6 + 12.5 + 12.5 Ö ½
3
= 12.5333cm3Ö ½
(d) (i) Moles of the acid
If 1000cm3 0.2 moles
12.5333cm3 0.2 x 12.5333 Ö1
1000
= 0.002506 moles Ö ½
(ii) Moles of sodium hydroxide
Mole ratio
H+ :OH–
1 : 1 Ö1
\0.002506 : 0.002506
Ie 0.002506 moles Ö ½
(e) Moles of acid that reacted with sodium carbonate
Ans (b) – ans (dii)
0.005 moles – 0.002506 moles Ö1
= 0.002494 moles Ö ½
(f) Molarity of A in terms of NaOH
If 25.0cm3 0.002506
The 1000cm3 0.002506 x 1000 Ö1
25cm3
= 0.10024M Ö ½
(g) CO32- (aq) + 2H+(aq) H2O (l) + CO2 (g)
[Unbalanced 0 mark
Missing state symbol ½ mark]
(h) (i) Moles of sodium carbonate
½ x 0.002494 Ö ½
= 0.001247 moles Ö ½
(ii) Molarity of A in terms of Na2CO3
If 25cm3 0.001247
Then 1000cm3 0.001247 x 1000 Ö1
25
= 0.04988M Ö ½
Observations | Inferences | |
2. (a) | – Solid melts Ö ½
– Burns in yellowÖ ½ sooty flame Ö ½ Max 1 ½ marks |
– Presence of either
C = C Ö ½ or C CÖ Max 1 mark |
(b) | – Dissolves Ö ½ into a colourless Ö ½ solution
Max 1 mark |
– Solid is polar Ö ½
Max ½ mark |
(c ) | – Acidified KMnO4 changes from purple to colourless Ö ½
Max ½ mark |
– Presence of either
C CÖ ½ or C CÖ ½ or R – OH Ö ½ Max 1 ½ marks |
(d) | – Acidified K2Cr2O7 changes from orange to green Ö ½
Max ½ mark |
– Presence of either
C CÖ ½ ; C CÖ ½ or R – OH Ö ½ Max 1 ½ marks |
(e) | – EffervencesÖ ½ production of colourless gas Ö ½
Max 1 mark |
H+Ö ½ / O
C OH present Max ½ mark |
(f) | pH 4 Ö ½
Max ½ mark |
Weakly acidic Ö ½
Max ½ mark |
3 (a) | – Colourless liquid on cooler parts of test tube Ö ½
– Colourless gas with pungent smell Ö ½ – Gas turns moist red litmus blue Ö ½ / Blue litmus remains blue Ö ½ |
– Hydrated salt Ö ½
– Presence of NH4+Ö ½ 1 |
(b) | – Solid dissolves into pale green solution Ö ½
– 1 |
– Polar solid Ö ½
– Presence of Fe2+Ö ½ 1 |
(c ) | -Green Ö ½ ppt insoluble Ö ½ in excess
– PPt turns brown on exposure to air Ö ½ 1 ½ |
– Presence of Fe2+Ö ½
– Fe2+ oxidized to Fe3+ by air Ö 1 1 |
(d) | – Green ppt Ö ½ insoluble in excess
– Ppt turns brown on exposure to air Ö ½ 1 ½ |
– Presence of Fe2+Ö ½
– Fe2+ oxidized to Fe3+ by air Ö ½ 1 |
(e) | – Pale green solution turns yellow Ö ½
– Brown Ö ½ ppt insoluble Ö ½ in excess 1 ½ |
– Presence of Fe3+Ö ½
½ |
(f) | – Formation of white ppt Ö ½ as residue and green solution as filtrate Ö ½
1 |
– Presence of Fe2+Ö ½
– Presence of either Ce–Ö ½ , SO42-Ö ½ or SO32-Ö ½ , CO32-Ö ½ Max 2 marks |
(g) | – White ppt forms Ö ½
½ |
SO42- present Ö ½
½ |
MOCKS 1 2023
MARKING SCHEME
233/1
CHEMISTRY
PAPER 1
THEORY
- (a) K 2. 8.8.2 √1mk
M 2.6 √1mk
(b) K 2+
M 2-
2 (a) Anode: I– (l) I2 (g) +2e–√1mk
Cathode: Pb2++ 2e– Pb (s)√1mk
- b) Increase in temperature increases the kinetic energy (1/2 mrk) of positive centres and electrons making them to vibrate more. These increase collisions of positive centres and electrons hence increased resistance (1/2mrk)
- Add water to the mixture and stir sodium chloride dissolve leaving copper (ii) oxide which is insoluble. (√1mk)
Filter(1/2) to remove copper (ii) oxide and sodium chloride as the filtrate
Evaporate the filtrate to saturation and cool to obtain sodium crystals (√1mk)
Dry them between filter papers/leave them in the open to dry (√1mk)
- Hot platinum wire glows red. (√1mk)
Brown fumes are observed (√1mk)
Reaction between oxygen gas and ammonia gas over platinum wire is exothermic. (1/2mrk)
Ammonia is oxidized to nitrogen (ii) oxide which reacts with excess oxygen to form nitrogen (iv) oxide,(1/2 mrk)
- a) A bond formed by two atoms/elements by share of electrons from one of the atoms/element(√1mk)
b)
- a) Remove / absorb carbon (iV) oxide (√1mk)
- b) 3Mg (s) + N2(g) Mg3N2 (s) (√1mk)
- c) Neon/ Argon (√1mk)
- a) But – 1 – ene (√1mk)
- b) Pent – 2 –ene (√1mk)
- c) Potassium manganate (VII) is decolourised/ Potassium manganate (VII) changes colour from purple to colourless (√1mk)
- a) The outer zone has complete combustion and hence hotter tha the middle zone forming the charred black part (1mrk) Middle zone has incomplete combustion and hence less hot forming unburnt part (√1mk)
- b) – Non – luminous flame is hotter than luminous flame (1mrk)
Non – luminous flame does not produce soot (1mrk) Any one (√1mk)
- a) Sulphuric (VI) acid react with marble (Calcium carbonate) forming insoluble calcium sulphate(1mrk) which form a coat over marble stopping any further reaction (√1mk)
- b) Oil is less dense (1/2) than water making oil float(1/2) on top hence continues to burn.
- 2XOH(aq) + H2SO4(aq) X2SO4 (aq) + 2 H2O(l)
XOH = 2 = 15 X M
H2SO4 1 20 X 0.045 (√1mk)
M = 2 X 20 X 0.045
1 X 15 = 0,12 moles/l (1/2)
1mole = 2.88
0.12 = 24 (1/2)
RFM of XOH = X + 16 + 1 (1/2)
X = 7 1/2)
- a) 2CxHy X CO2 + y/2 H2O
X = 6
2 = 3 (1/2)
Y = 12
3 = 6 (1/2)
MF = C3H6 (1/2)
Structural fprmula = CH3 CH = CH2 (1/2)
- b) Alkenes
- on the diagram
- a) √1mk
- b) arrow from zinc half-cell towards copper half cell √1mk
- c) Zn(s) + Cu2+(aq) Zn2+(aq) + Cu(s) √1mk
- (i) Froath floatation √1mk
(ii) Concetrating the mineral ore by making impurities to sink atb the bottom. √1mk
- (a) Exp. 1 – The colour of dry cloth did not turn to white/ cloth not bleached, because of the absence of hypochloric (I) acid which is responsible for bleaching
(b) Exp 2 – Wet cloth turned white due to bleaching as chlorine dissolves in water to form hypochloric(I) acid√1mk
- b) Cl2(g) + H2O(g) + Dye {Dye + [O]} + 2HCl(g) √1mk
- (a) Solubility is the maximum mass in grams of solute that will dissolve in 100g ofvwater at a given temperature/ is the mass in grams of solute required to make a saturated solution with 100g of water at given temperature. √1mk/
(b) Mass of solid Y = 30.4 – 26.2
= 4.2g (1/2mrk)
Mass of water in the solution = 42.4 – 30.4
= 12g (1/2 mrk)
12 g of water dissolve 4.2g solid Y
100g of ware will dissolve 100 x 4.2 (1/2mrk)
12
= 35g / 100g of water (1/2mrk)
- AH0f(CO) + AH0c(CO) = AH0c(C)
-105 + AH0c(CO) = -393 √1mk
AH0c(CO) = -393 + 105 √1mk
= -188kJMol-1 √1mk
- a) Water √1mk
b)The delivery tube should first be removed √1mk to avoid sucking back of liquid M √1mk
- a) Atomic mass of Y 2 + 3 = a + 1
a = 4 √1mk
Atomic number 1 + 1 = b + 0
b = 2 √1mk
- b) Nuclear fusion √1mk)
V1 = 4dm3 ; P1 = 152mmHg ; V2 = 2dm3 ; T1 = 250K ; T2 = 500K P2 = ?
152 x 4 = P2 x 2
250 500 √1mk
P2 = 152 x4 x 500
250 x 2 √1mk
= 608mmHg √1mk
- a) (i) Liquid H is Water √1mk
(ii) Gas G is Nitrogen (i) oxide √1mk
- b) turn white anhydrous copper (II) sulphate to blue / Turns blue cobalt(II) chloride to pink √1mk
- a) Amphoteric oxide √1mk
- b) Lead (II) oxide / Zinc oxide / Aluminium (III) oxide (Any one) √1mk
- a) Rate of forward reaction equals to the rate of backward reaction. √1mk
- b) Orange colour of the solution intensifies √1mk
Equilibrium shift to the left/ backward reaction is favoured to replace OH– that react with H+ √1mk
Element Ba S O
% composition 58.81 13.72 24.47
RAM 13732 16
No. of moles 58.81 13.72 24.47 (1/2mrk)
137 32 16
0.4293 0.4281 1.768
Mole ratio 1 1 4 (1/2mrk)
E . F. BaSO4(√1mk)
- (i) A white ring/ solid (1/2mrk) was formed inside the combustion tube closer to the cotton wool soaked in concentrated hydrochloric acid (1/2mrk). Ammonia is lighter/less dense than hydrochloric acid hence diffuse faster (√1mk)
(ii) NH3 (g) + HCl(g) NH4Cl(s) (√1mk)
- (i) The yield of AB is increased. (√1mk)
The forward reaction is accompanied by a decrease in volume(1/2mrk). Equilibrium shifts to the right following increase of the forward reaction (1/2mrk)
(ii) The yield of AB is increased’ (√1mk)
The forward reaction is exothermic.(1/2mrk) Decrease in temperature favours the forward reaction, equilibrium shifts to the right.(1/2mrk)
- (a) Deliquescence (√1mk)
(b) Efflorescence (√1mk)
(c) Hygroscopy (√1mk)
- a) A – Nitrogen (IV) oxide/ NO2(√1mk)
B – Oxgygen/ O2(√1mk)
- b) 2ZnNO3 (g)2ZnO(s) + 4 NO2 (g) + O2(g) (√1mk)
- Tin (√1mk)
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