Form 3 Chemistry Exams and Marking Schemes Free

Name: …………….…………………………………….………….. Adm No:……………………

Candidate’s signature: …….………

Date: ………..……………………….

 

JOINT EVALUATION EXAMINATION

233/3

Chemistry

Paper 3

 

Time: 2Hours

 

Instructions

 

1. Write your name, admission number and sign in the spaces provided above
2. Answer all questions in the spaces provided
3. Non-programmable silent electronic calculators and KNEC mathematics tables may be used.
4. All questions should be answered in English

 

 

For Examiners only

QUESTION 1	14
QUESTION 2	6
TOTAL	20

 

 

 

 

 

 

1. 1. You are provided with:

• 5 g of impure anhydrous sodium carbonate labelled as solid X
• 2M hydrochloric acid labelled as solution Y
• 4M sodium hydroxide solution as solution Z

You are required to determine the percentage purity of solid X.

Procedure

1. Using a measuring cylinder place 80cm³ of solution Y in a beaker.
2. Add all solid X and stir the solution using a stirring rod until effervescence stops.

• Transfer this solution into a 250 cm³ volumetric flask and add distilled water to the mark. Label this as solution T.

1. Place solution T in a clean burette.
2. Using a pipette filler, put 25 cm³ of solution Z in a conical flask.
3. Add 2 drops of methyl-orange and titrate using solution T.

• Repeat the titration two more times and complete the table below.

 

	I	II	III
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of solution T used (cm3)

(4mks)

1. a) Calculate the:
2. Average volume of solution T used                                     (1 mark)

 

 

 

 

1. The number of moles of solution Z used in titration (2 mark)

 

 

 

 

• Concentration of solution T in moles per liter. (2 marks)

 

 

 

 

 

1. Calculate the mass of sodium carbonate that reacted with solution Y. (Na= 23, C= 12, O= 16)                                                                                                       (3marks)

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

1. Work out the percentage purity of solid X.                         (1 mark)

 

 

1. b) Write the ionic equation between solid X and solution Y. (1 mark)

 

 

2. You are provided with solid L. Carry out the test below and record your observations and inferences in the spaces provided.
3. a) Describe solid. (2 marks)

 

1. b) Place half spatula of L in a non-luminous flame of a Bunsen burner.

Observations	Inference
(1/2 mark)	(1/2 mark)

 

 

1. c) Dissolve the remaining solid L in the distilled water and divide the solution into four portions.
2. To the fourth portion, add few drops of acidified potassium chromate (vii) and warm.

Observations	Inference
(1/2 mark)	(1/2 mark)

 

1. To the second portion, add few drops of bromine water and warm.

Observations	Inference
(1/2 mark)	(1/2 mark)

 

 

 

 

• To the third portion add few drops of acidified potassium manganite (vii) and warm.

Observations	Inference
(1/2 mark)	(1/2 mark)

 

1. To the fourth portion add a quarter spatula end-full of sodium hydrogen carbonate.

Observations	Inference
(1/2 mark)	(1/2 mark)

__________________________________________________________________________________

MARKING SCHEME

CHEMISTRY PRACTICAL

 

	I	II	III
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of solution T used (cm3)

 

1. Complete table ……………………………………………………………….(1mk)

Complete table with 3 titrations done – 1mk

InComplete table with 2 titrations done  – 1mk

incomplete table with 1 titration done – 0mks

 

Penalize ½ mk once for

• Inverted table
• Wrong anthmetic
• Unrealistic titre values ( below 1 or above 50 unless explained)

 

1. Use of decimals………………………………………………………………..1mk

• Accept 1 or 2 d.p uses consistently otherwise penalize fully
• If 2 d.p used the 2^ndp should be either 0 or 5 otherwise penalize fully

1. c) Accuracy ……………………………………………………………………….1mk

Compare the candidatestitre values with the S.V

• If any value is within +- 0.1 award 1mk
• If within + -0.2 award ½ mk
• If beyond +- 0.2 award zero mark

 

1. Principles of averaging ……………………………………………………….1mk

1f 3 consistent titrations done and averaged                               1mk

If 3 titrations done but only 2 are consistent and averaged   (1mk)

 

If only two titrations done, are consistent and averaged     (1mk)

If 3 titrations done and are consistent but only 2 are averaged    ( 0mk)

If 3 inconsistent titres averaged                                                 ( 0mk)

1f 2 inconsistent titres averaged                                                (0mk)

 

1. Final answer accuracy……………………………………………………………..1mk

Compare the candidates correct average titre with S.V

• If within +- 0.1 of S.V (1mk)
• If within +- 0.2 of S.V ( ½ mk)
• If beyond +- 0.2 of S.V ( 0mk)

 

 

1. a) Calculate the:
2. Average volume of solution T used                                     (1 mark)

Captured in principal of averaging

1. The number of moles of solution Z used in titration (1 mark)

 

• Concentration of solution T in moles per liter. (2 marks)

1. Calculate the mass of sodium carbonate that reacted with solution Y. (Na= 23, C= 12, O= 16)                                                                                                       (3marks)

 

1. Work out the percentage purity of solid X.                         (1 mark)

x 100

1. b) Write the ionic equation between solid X and solution Y. (1 mark
2. You are provided with solid L. Carry out the test below and record your observations and inferences in the spaces provided.
3. a) Describe solid. (2 marks)

 

1. b) Place half spatula of L in a non-luminous flame of a Bunsen burner.

Observations	Inference
Solid melts and burns with a yellow sooty flame       (1/2 mark)	(1/2 mark)

 

1. c) Dissolve the remaining solid L in the distilled water and divide the solution into four portions.
2. To the fourth portion, add few drops of acidified potassium chromate (vi) and warm.

Observations	Inference
Orange acidified potassium chromate VI does not change to green Reject persist or remains or no color change, no observable change       (1/2 mark)	R-OH  absent       (1/2 mark)

 

1. To the second portion, add few drops of bromine water and warm.

 

Observations	Inference
Yellow bromine water changes to colorless / decolorized                     (1/2 mark)	(1/2 mark)

 

 

 

 

• To the third portion add few drops of acidified potassium manganite (vii) and warm.

Observations	Inference
Purple acidified potassium manganate VII changes to colourless       (1/2 mark)	(1/2 mark)

 

1. To the fourth portion add a quarter spatula end-full of sodium hydrogen carbonate.

Observations	Inference
Effervescence / bubbles  produced     (1/2 mark)	R-COOH         (1/2 mark)

__________________________________________________________________________________________

JOINT EVALUATION EXAMINATIONS

CHEMISTRY PAPER THREE CONFIDENTIAL

1.Provide each candidate with

5. Exactly 5.0 g of impure anhydrous sodium carbonate in a stoppered container and label as solid X.
6. 100 cm³ of 2M hydrochloric acid labeled as solution Y.

• About 100 cm³ of 0.4M sodium hydroxide

1. 5 g of maleic acid in a stoppered container labeled as solid L
2. 1 burette
3. 1 pipette

• 10ml measuring cylinder
• Distilled in wash bottle

1. 6 test tubes
2. 1 boiling tube
3. Red and blue litmus papers

• 1 clamp and stand

2. In addition to the above reagents, candidates should access to:
3. 1M acidified potassium chromate (vi)
4. 1M acidified potassium manganite (vii)

• Bromine water

1. Methyl –orange indicator
2. Preparation of solutions

    2 M HCl acid

• Dissolve 172cm³ of concentrated hydrochloric acid in enough distilled water and dilute to one litre

    Bromine water

• Dissolve 10 cm ³ of liquid bromine in 100cm³ of distilled water and store in a dark bottle.

    Acidified potassium chromate (vi)

• Dissolve 25 g of potassium chromate (vi) in 200 cm³ of 2M Sulphuric (vi) acid and dilute to one litre solution

    Acidified potassium manganite (vii)

• Dissolve 3.16 g of potassium manganite (vii) in 200 cm³ of 2 M Sulphuric (vi) acid and dilute to one litre.

 

 

Methyl orange

• Dissolve 2 g of methyl orange solid in a litre of dissolved water to form a solution. Filter the resulting mixture

 ________________________________________________________

CHEMISTRY

PAPER 1, 233/1

FORM THREE (3), END OF YEAR

TIME:2HRS

 

 

Name: ……………………………………………

AdmNo: .……………Class………….

Signature: ……………………………………Date: ……………………

 

 

 

Instructions to candidate

1. Write your name, admission number, and stream in the spaces provided.
2. Answer ALL questions in the spaces provided
3. All workingsMUST be clearly shown where applicable
4. KNEC mathematical tables and silent non-programmable electronic calculators may be used
5. This paper consists of 12 printed pages
6. The candidate should check the question paper to ascertain that all the pages are printed as indicated and that no question is missing

 

FOR EXAMINERS’ USE ONLY

Question	Maximum Score	Candidate’s Score
1 – 29	80

 

 

 

 

1. Given a mixture of sodium chloride, silver chloride, and ammonium chloride, describe how each component can be obtained.       (3 Marks)

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

2. Air was passed through several reagents as shown below.

 

I Concentrated potassium hydroxide solution

II Heated excess copper turnings

III Heated excess magnesium powder.

 

 

 

 

 

 

 

 

gas

collected

 

 

1. What is the role of concentrated potassium hydroxide?         (1mk)

 

 

1. Write an equation that takes place in step III with Magnesium powder.         (1mk)

 

 

(c) Name one gas that was collected from the process.                                                                      (1mk)

 

3. The diagram below represents the Frasch process. Study it and answer the questions that follow

Sulphur deposit

A

C

B

 

1. Name;

A                                                                                                                                            ( ½mk)

B                                                                                                                                            ( ½mk)

C                                                                                                                                            ( ½mk)

1. Why is C pumped to the sulphurdeposit.                               ( ½ mk)

 

 

• Which property of sulphur enables it to be extracted by the method above. (1mk)

 

 

4. Give the systematic name of the following compounds A and B (2 Marks)

A                                         B

A …………………………………………….

B …………………………………………….

 

 

5. (a) Define Gay-Lussac’s law (1 Mark)

…………………………………………………………………………………………………..

…………………………………………………………………………………………………….

…………………………………………………………………………………………………..

• In an experiment a mixture of 126.0cm³ of nitrogen gas and 120.0cm³ of hydrogen gas was heated in the presence of iron catalyst. Determine the composition of the final gaseous mixture.                                     (2 Marks)

…………………………………………………………………………………………………..

…………………………………………………………………………………………………..

……………………………………………………………………………………………………

…………………………………………………………………………………………………..

 

 

 

 

 

 

6. The table below shows certain properties of substances M, N, K, and L.

Substance	Melting point (oC)	Solubility in water	Electrical conductivity
M	-119	Soluble	Solution does not conduct
N	1020	Soluble	Solution conducts
K	1740	Insoluble	Does not conduct
L	1600	Insoluble	Conducts at room temperature

 

Which of the substances:

1. Is a metal (½ Mark)

……………………………………………………………………………………………

1. Has a simple molecular structure (½ Mark)

…………………………………………………………………………………………..

1. Has a giant covalent structure (½ Mark)

……………………………………………………………………………………………

 

1. Has a giant ionic structure (½ Mark)

……………………………………………………………………………………………

7. A polymer has the following structure
8. Draw and name the monomer (2 Marks)

 

 

 

 

1. Draw the repeating unit of the polymer (2 Marks)

 

 

 

 

8. Draw dot (•) and cross (×) diagrams to show bonding in:
9. Magnesium chloride (2 Marks)

 

 

 

 

 

1. phosphonium ion (PH₄⁺) (2 Marks)

 

 

 

 

9. (a). A piece of burning magnesium was introduced into a jar of nitrogen. State and explain the observation made       (2 Marks)

………………………………………………………………………………………………..

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

 

 

• Water was added to the product of the reaction in a) and the resultant solution tested with red and blue litmus papers. State and explain the observation made             (2 Marks)

……………………………………………………………………………………………….

……………………………………………………………………………………………….

……………………………………………………………………………………………….

10. Briefly describe how sodium carbonate powder can be obtained in the laboratory starting with concentrated sodium hydroxide solution                   (2 Marks)

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

………………………………………………………………………………………………………

 

 

 

 

11. The sketch graph below shows the relationship between pressure and temperature of a gas in a fixed volume container.
12. State the relationship between pressure and temperature that can be deduced from the graph             (1 Mark)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

1. Using the kinetic theory of matter, explain the relationship shown by the sketch graph             (2 Marks)

…………………………………………………………………………………………………..

…………………………………………………………………………………………………..

…………………………………………………………………………………………………..

 

 

12. (a) Group VIII elements are said to be inert. Explain. (1 Mark)

…………………………………………………………………………………………………..

…………………………………………………………………………………………………..

………………………………………………………………………………………………….

• In terms of structure and bonding, explain why group VIII elements exist as gases at room temperature             (2 Marks)

………………………………………………………………………………………………………

…………………………………………………………………………………………………….

13. Nitric (V) acid may be prepared in the laboratory by the action of concentrated sulphuric (VI) acid in a suitable nitrate and distilling off the nitric (V) acid
14. Why does the setup only consist of apparatus made of glass? (1 Mark)

……………………………………………………………………………………………….

……………………………………………………………………………………………….

……………………………………………………………………………………………….

1. Pure nitric (V) acid is colourless but the product in the collection vessel is yellow. Explain             (1 Mark)

…………………………………………………………………………………………………

………………………………………………………………………………………………….

1. Why is it possible to separate nitric (V) acid from sulphuric (VI) acid in the setup?(1 Mark)

…………………………………………………………………………………………………..

………………………………………………………………………………………………….

 

14. Name the catalyst used in the following processes:
15. Large scale manufacture of ammonia gas in the Haber process (1 Mark)

…………………………………………………………………………………………….

1. Large scale manufacture of concentrated sulphuric (VI) acid in the Contact process (1 Mark)

…………………………………………………………………………………………………

1. Laboratory preparation of oxygen using hydrogen peroxide             (1 Mark)

……………………………………………………………………………………………….

 

15. What mass of magnesium carbonate would remain if 15.0g of magnesium carbonate reacts with 25cm³ of 4M hydrochloric acid solution?       (3 Marks)

 

 

 

 

 

16. The setup below was used to investigate the reaction of a certain gas with lead (II) nitrate solution
17. Identify gas A (1 Mark)

……………………………………………………………………………………………..

1. State the observation made in the trough containing lead (II) nitrate solution (1 Mark)

…………………………………………………………………………………………………..

1. Write an ionic equation for the reaction occurring in the trough (1 Mark)

…………………………………………………………………………………………………

17. Element Q reacts with dilute acids, but not with cold water. Element R does not react with dilute acids. Element S displaces element P from its oxide. P reacts with cold water. Arrange the four elements in order of reactivity, starting with the most reactive element. (2 Marks)

……………………………………………………………………………………………………..

……………………………………………………………………………………………………..

18. A fixed mass of a gas occupies 200cm³ at 0^oC and 740mmHg pressure. Calculate its volume at -48^oC and 780mmHg.       (3 Marks)

 

 

 

 

 

 

19. In an experiment, a sample of an oxide of lead was heated over coke for some time. The following results were obtained:

Mass of the oxide before heating                         = 8.92g

Mass of residue after heating                   = 8.28g

1. Determine the empirical formula of the oxide of lead (Pb = 207, O = 16)   (2 Marks)

 

 

 

 

1. Write an equation for the reaction in the experiment above             (1 Mark)

 

 

 

 

20. The information in the table below relates to the physical properties of the chlorides of certain elements.

Formula of compound	NaCl	MgCl2	AlCl3	SiCl4	PCl3	SCl2
Boiling point (oC)	1470	1420	Sublimes at 180oC	60	75	60
Melting point (oC)	800	710		-70	-90	-80

 

1. Select two chlorides that are liquid at room temperature   (2 Marks)

…………………………………………………………………………………………………..

1. Explain why AlCl₃ has a much lower melting point than MgCl₂, although both aluminium and magnesium are metals.                         (2 Marks)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

…………………………………………………………………………………………………

 

 

21. 400cm³ of a gas D diffuses through a porous plug in 50 seconds, while 600cm³ of oxygen gas diffuses from the same apparatus in 30 seconds. Calculate the relative molecular mass of gas D. (O = 16)                                                                                                                (2 Marks)

 

 

 

22. Calculate the volume of oxygen produced when 10g of silver nitrate was completely decomposed by heating at standard temperature and pressure                                           (Ag = 108, N = 14, O = 16, Molar gas volume at s.t.p. = 22400cm³)                        (3 Marks)

 

 

 

 

 

 

23. The electron arrangement of ions W³⁺and Z^2- are 2.8 and 2.8.8 respectively.
24. In which groups do elements W and Z belong? (1 Mark)

……………………………………………………………………………………………..

1. Write the formula of the compound that would be formed between W and Z (1 Mark)

…………………………………………………………………………………………………

24. 20cm³ of a solution containing 2.7g/dm³ of an alkali XOH completely reacted with 25cm³ of 0.045M sulphuric (VI) acid. Calculate the relative atomic mass of element X (O = 16, H = 1)                               (3 Marks)

 

 

 

 

 

25. Calculate the number of sulphate ions in 150cm³ of 0.1M aluminium sulphate, Al₂(SO₄)₃(3 Marks)

(L = 6.023 × 10²³)

 

 

 

26. The following apparatus was set up to investigate the percentage of oxygen in air by slowly passing 100cm³ of air from syringe A to syringe B and then back until the volume of air remained constant. Study it and use it to answer the questions that follow.
27. Identify the mistake in the setup (1 Mark)

……………………………………………………………………………………………..

1. Why was the air moved slowly from syringe A to syringe B and vice versa? (1 Mark)

………………………………………………………………………………………………

………………………………………………………………………………………………

1. Write an equation for the reaction that took place in the combustion tube after the mistake was corrected                         (1 Mark)

…………………………………………………………………………………………………

 

27. A luminous flame produces bright yellow light. Explain (1 Mark)

………………………………………………………………………………………………………

………………………………………………………………………………………………………

………………………………………………………………………………………………………

 

28. Magnesium reacts by losing its 2 valence electrons. How does its 1^st and 2^nd ionization energy compare? Explain                   (2 Marks)

……………………………………………………………………………………………………..

 

 

 

 

 

 

 

 

29. The apparatus below was used for the preparation of iron (III) chloride in the laboratory. Study it and use it to answer the questions that follow.

 

1. Why is it preferred to use calcium oxide rather than calcium chloride in the guard tube?             (2 Marks)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

1. What property of iron (III) chloride makes it possible to be collected as shown in the diagram?             (1 Mark)

…………………………………………………………………………………………………..

………………………………………………………………………………………………….

…………………………………………………………………………………………………..

___________________________________________________________________________________________________

 

CHEMISTRY PAPER 1 MARKING SCHEME

FORM 3,END YEAR

 

1. Given a mixture of sodium chloride, silver chloride, and ammonium chloride, describe how each component can be obtained.                                     (3 Marks)

• Heat the mixture to sublime ammonium chloride and cool the vapour against a cool surface to deposit it.
• Add water to the remaining mixture and stir to dissolve sodium chloride. Filter the mixture to obtain sodium chloride solution as a filtrate and silver chloride as a residue.
• Dry the residue between fresh filter papers.
• Heat the filtrate to saturation and allow to cool to obtain crystals of sodium chloride.

[marking points at half mark each]

2. (a) To remove carbon (IV)oxide gas

 

(b) 3Mg(s) + N₂(g) → Mg₃N₂(s)

 

(c) Argon

 

3. (a) A-Hot compressed air

 

• Molten sulphur and water

 

• Super heated water

 

(b) To melt sulphur deposit

(c) sulphur has low melting point

 

 

 

 

 

 

 

 

4. Give the systematic name of the following compounds             (2 Marks)

2,3-dibromopentane                 2-methylbutane

5. (a) Define Gay-Lussac’s law (1 Mark)

When gases react at constant temperature and pressure, they do so in volumes that bear a simple ratio to one another, and to the volumes of the product if all the products are gaseous.

• In an experiment a mixture of 126.0cm³ of nitrogen gas and 120.0cm³ of hydrogen gas was heated in the presence of iron catalyst. Determine the composition of the final gaseous mixture.                                     (2 Marks)

 

 

 

 

 

 

 

6. The table below shows certain properties of substances M, N, K, and L.

Substance	Melting point (oC)	Solubility in water	Electrical conductivity
M	-119	Soluble	Solution does not conduct
N	1020	Soluble	Solution conducts
K	1740	Insoluble	Does not conduct
L	1600	Insoluble	Conducts at room temperature

 

 

 

Which of the substances:

1. Is a metal (½ Mark)L
2. Has a simple molecular structure (½ Mark)

M

1. Has a giant covalent structure (½ Mark)

K

1. Has a giant ionic structure (½ Mark)

N

7. A polymer has the following structure
8. Draw and name the monomer (2 Marks)

 

 

 

1. Draw the repeating unit of the polymer (2 Marks)
2. Draw dot (•) and cross (×) diagrams to show bonding in:
3. Magnesium chloride (2 Marks)

or

 

 

 

1. Phophonium ion (PH₄⁺) (2 Marks)
3. A piece of burning magnesium was introduced into a jar of nitrogen. State and explain the observation made                         (2 Marks)

The magnesium continues to burn in nitrogen. Magnesium reacts with nitrogen to form magnesium nitride.

1. Water was added to the product of the reaction in a) and the resultant solution tested with red and blue litmus papers. State and explain the observation made             (2 Marks)

Red litmus paper turns blue while blue litmus paper remains blue. Magnesium nitride reacts with water to form magnesium hydroxide and ammonia, which are alkaline.

 

10. Briefly describe how sodium carbonate powder can be obtained in the laboratory starting with concentrated sodium hydroxide solution                                     (2 Marks)

Bubble a limited amount of carbon (IV) oxide gas through the sodium hydroxide solution to obtain sodium carbonate solution. Heat the solution to evaporation to allow formation of sodium carbonate powder.

11. The sketch graph below shows the relationship between pressure and temperature of a gas in a fixed volume container.
12. State the relationship between pressure and temperature that can be deduced from the graph             (1 Mark)

An increase in temperature results in an increase in pressure of a fixed mass of gas.

1. Using the kinetic theory of matter, explain the relationship shown by the sketch graph             (2 Marks)

An increase in temperature results to an increase in kinetic energy of gas particles. The number of collisions between the particles and the walls of the container increases, hence,an increase in pressure.

12. (a) Group VIII elements are said to be inert. Explain.             (1 Mark)

They have fully occupied outermost energy levels hence do not lose or gain electrons

• In terms of structure and bonding, explain why group VIII elements exist as gases at room temperature             (2 Marks)

Their atoms are held together by weak Van der Waal’s forces that require little energy to break. At room temperature, the energy is sufficient to break these forces hence atoms are free to move.

13. Nitric (V) acid may be prepared in the laboratory by the action of concentrated sulphuric (VI) acid in a suitable nitrate and distilling off the nitric (V) acid
14. Why does the setup only consist of apparatus made of glass? (1 Mark)

Nitric acid attacks rubber and other materials but glass is inert.

1. Pure nitric (V) acid is colourless but the product in the collection vessel is yellow. Explain             (1 Mark)

Some nitric (V) acid decomposes in the presence of heat to yield nitrogen (IV) oxide which is brown and later condenses to form yellow dinitrogen tetra-oxide. The dinitrogen tetra-oxide dissolves in the acid to yield the yellow colouration.

1. Why is it possible to separate nitric (V) acid from sulphuric (VI) acid in the setup?(1 Mark)

Nitric (V) acid is volatile and therefore easily vaporises while sulphuric (VI) acid is not volatile and does not easily vaporise.

14. Name the catalyst used in the following processes:
15. Large scale manufacture of ammonia gas in the Haber process (1 Mark)

Finely divided iron catalyst

1. Large scale manufacture of concentrated sulphuric (VI) acid in the Contact process (1 Mark)

Platinum or Vanadium (V) oxide.

1. Laboratory preparation of oxygen using hydrogen peroxide             (1 Mark)

Manganese (IV) oxide

 

15. What mass of magnesium carbonate would remain if 15.0g of magnesium carbonate reacts with 25cm³ of 4M hydrochloric acid solution?                         (3 Marks)
16. The setup below was used to investigate the reaction of a certain gas with lead (II) nitrate solution
17. Identify gas A (1 Mark)

Hydrogen chloride gas

 

 

1. State the observation made in the trough containing lead (II) nitrate solution (1 Mark)

A white precipitate is formed in the solution

1. Write an ionic equation for the reaction occurring in the trough (1 Mark)

Pb²⁺_(aq) + 2Cl^–_(aq)à PbCl_{2 (aq)}

 

 

17. Element Q reacts with dilute acids, but not with cold water. Element R does not react with dilute acids. Element S displaces element P from its oxide. P reacts with cold water. Arrange the four elements in order of reactivity, starting with the most reactive element. (2 Marks)

S à P à Q à R

18. A fixed mass of a gas occupies 200cm³ at 0^oC and 740mmHg pressure. Calculate its volume at -48^oC and 780mmHg.                         (3 Marks)
19. In an experiment, a sample of an oxide of lead was heated over coke for some time. The following results were obtained:

Mass of the oxide before heating                         = 8.92g

Mass of residue after heating                   = 8.28g

1. Determine the empirical formula of the oxide of lead (Pb = 207, O = 16)   (2 Marks)

 

1. Write an equation for the reaction in the experiment above             (1 Mark)

2PbO _(s) + C _(s)à 2Pb _(s) + CO_{2 (g)}

 

 

 

 

20. The information in the table below relates to the physical properties of the chlorides of certain elements.

Formula of compound	NaCl	MgCl2	AlCl3	SiCl4	PCl3	SCl2
Boiling point (oC)	1470	1420	Sublimes at 180oC	60	75	60
Melting point (oC)	800	710		-70	-90	-80

 

 

1. Select two chlorides that are liquid at room temperature   (2 Marks)

SiCl₄, PCl₃, SCl₂

[the first two of the candidate’s answer]

1. Explain why AlCl₃ has a much lower melting point than MgCl₂, although both aluminium and magnesium are metals.                         (2 Marks)

AlCl₃has its atoms bonded covalently to each other to form a simple molecule, while MgCl₂ experiences ionic bonding. AlCl₃ therefore has weak Van der Waal’s forces that require little energy to weaken while MgCl₂ has strong ionic bonds that require a lot of energy to weaken.

21. 400cm³ of a gas D diffuses through a porous plug in 50 seconds, while 600cm³ of oxygen gas diffuses from the same apparatus in 30 seconds. Calculate the relative molecular mass of gas D. (O = 16)                                                                                                                      (2 Marks)

 

 

22. Calculate the volume of oxygen produced when 10g of silver nitrate was completely decomposed by heating at standard temperature and pressure                                                             (Ag = 108, N = 14, O = 16, Molar gas volume at s.t.p. = 22400cm³)              (3 Marks)
23. The electron arrangement of ions W³⁺and Z^2- are 2.8 and 2.8.8 respectively.
24. In which groups do elements W and Z belong? (1 Mark)

W – Group III                    Z – Group VI

1. Write the formula of the compound that would be formed between W and Z (1 Mark)

W₂Z₃

24. 20cm³ of a solution containing 2.7g/dm³ of an alkali XOH completely reacted with 25cm³ of 0.045M sulphuric (VI) acid. Calculate the relative atomic mass of element X (O = 16, H = 1)                                                 (3 Marks)

 

 

 

 

 

25. Calculate the number of sulphate ions in 150cm³ of 0.1M aluminium sulphate, Al₂(SO₄)₃(3 Marks)

(L = 6.023 × 10²³)

 

26. The following apparatus was set up to investigate the percentage of oxygen in air by slowly passing 100cm³ of air from syringe A to syringe B and then back until the volume of air remained constant. Study it and use it to answer the questions that follow.
27. Identify the mistake in the setup (1 Mark)

Use of magnesium in the combustion tube

 

1. Why was the air moved slowly from syringe A to syringe B and vice versa? (1 Mark)

To ensure most of its active part reacted with the metal in the combustion tube

1. Write an equation for the reaction that took place in the combustion tube after the mistake was corrected                         (1 Mark)

2Cu _(s) + O_{2 (g)}à 2CuO _(s)

27. A luminous flame produces bright yellow light. Explain (1 Mark)

Due to insufficient supply of air, unburnt carbon particles heat up and glow to give yellow light

 

 

 

 

 

 

28. Magnesium reacts by losing its 2 valence electrons. How does its 1^st and 2^nd ionization energy compare? Explain                                                 (2 Marks)

The 2^nd ionization energy is higher than the 1^st ionization energy. After losing the first valence electron, there are fewer electrons for the number of protons left, resulting in an increase in the effective nuclear force of attraction that holds the remaining electrons more tightly.

29. The apparatus below was used for the preparation of iron (III) chloride in the laboratory. Study it and use it to answer the questions that follow.
30. Why is it preferred to use calcium oxide rather than calcium chloride in the guard tube?             (2 Marks)

Apart from preventing moisture from entering the collection vessel, calcium oxide reacts with excess chlorine to minimise its emission to the environment.

1. What property of iron (III) chloride makes it possible to be collected as shown in the diagram?             (1 Mark)

It sublimes when heated and deposits when cooled

___________________________________________________________________________________________

Name: ………………………………………………. Adm No: ………

school…………………………………………………………………

Class: ………Candidate’s Sign: …………………Date: …………

233/2

CHEMISTRY

PAPER 2

TERM 3 –

 

TIME: 2 HOURS

 

 

JOINT EXAMINATION

 

INSTRUCTIONS TO THE CANDIDATES:

• Write your name and admissionnumber in the spaces provided above
• Sign and write the date of examination in the spaces provided.
• Answer all the questions in the spaces provided.
• All working must be clearly shown where necessary.
• Mathematical tables and electronic calculators can be used.

 

For Examiners Use Only

 

Question	Maximum score	Candidate’s score
1	13
2	12
3	11
4	12
5	11
6	12
7	9
Total	80

1. The grid below shows a section of the periodic

K	L				M		N	P
	Q		R	S		T	V
W

1. Name the family into which element P belongs to             (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

1. Which two elements forms the most soluble carbonates                         (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

1. With a reason, identify elements in period 3 with the largest atomic radius (2mks )

……………………………………………………………………………………………………………………………………………………………………………………………………

1. Write the formula of the compound formed between Q and M (1mk )

……………………………………………………………………………………………………………………………………………………………………………………………………

1. State two uses of element R and for each use , state property of element R that makes lts possible for the use

• Use                                   (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

Property                                               (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

• Use             (1mk)

…………………………………………………………………………………………………………………………………………………………………………………………………

Property                                 (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

1. Using dots and cross, showbonding in the compound formed between Q and oxygen (2mks )

 

 

 

 

 

 

 

1. In terms of structure and bonding explain why the oxides of element Thas relatively low boiling points                                                                         (2mks)

…………………………………………………………………………………………………………………………………………………………………………………………………..

…………………………………………………………………………………………………………………………………………………………………………………………………….

2. (a) Name the following compounds (3mks)

• CH₃CH₂CH₂COOH

…………………………………………………………………………………………………

…………………………………………………………………………………………………

• CH₃CH₂OOCCH₂CH₃

…………………………………………………………………………………………………

 

1. b) Two types of detergents P and Q can be represented as

P:  R COONa

 

(i) Identify each type of the detergent                                                                  (2mks)

……………………………………………………………………………………………………………………………………………………………………………………………………

(ii)Which of the two detergents is the best to use with hard water? Give a reason                                            (2mks)

………………………………………………………………………………………………

………………………………………………………………………………………………

(iii)     State one advantage of detergent P                                                            (1mk)

………………………………………………………………………………………………

………………………………………………………………………………………………

(iv)    State one disadvantage of detergent Q                                                     (1mk)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

(c)   An hydrocarbon can be represented as follows

(i)            Identifythe hydrocarbon                                                     (1mk)

………………………………………………………………………………………………

(ii) Name two reagents that can reacted together to generate the hydrocarbon    (2mks)

……………………………………………………………………………………………………………………………………………………………………………………………………

3.(a)Name two apparatus that can be used for determining mass in a laboratory    (2mks)

…………………………………………………………………………………………………………………………………………………………………………………………………

(b)       One of the flames produced by Bunsen burner is the luminous flame

1. i) Explain why this flame is very bright                                                 (1mk )

…………………………………………………………………………………………………

………………………………………………………………………………………………

1. ii) State two disadvantages of the luminous flame (2mks)

…………………………………………………………………………………………………………………………………………………………………………………………………….

 

(c)       Air is usually one of the substances that is considered as a mixture

(i)Identify the two most abundant component of air                               (2mks )

……………………………………………………………………………………………………………………………………………………………………………………………………

 

(ii)       Give two reasons why the air is considered as a mixture                             (2mks)

…………………………………………………………………………………………………………………………………………………………………………………………………

(iii)      One of the components of air is carbon (iv) oxide. Describe an experiment that can be used to prove the presence of carbon (iv) oxide in the air                                               (2mks)

…………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………..

4(a) The diagram below shows the process used to obtain Sulphur from underground deposits

 

 

 

 

 

 

 

 

 

1. i) Name the above process used to obtain Sulphur from the underground deposits (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

1. ii) Name the substance passed through pipe

A                      (1mk)

…………………………………………………………………………………………………

B                                        (1mk)…………………………………………………………………………………………………

iii) State two properties of Sulphur that makes it possible to extract using the above process                                                                                                                         (2mks)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

1. b) The diagram below shows the contact process used in the manufacture of concentrated sulphuric(vi) acid

 

 

 

 

 

 

 

 

 

 

 

i)Identify the following:

1. a) SubstanceQ formed in the burner             (1mk)

…………………………………………………………………………………………………            b)         ChamberT                                                                                           (1mk)

…………………………………………………………………………………………………            c)         Substance R                                                                                        (1mk)

…………………………………………………………………………………………………

1. d) Substance S                                                                                        (1mk)

………………………………………………………………………………………………… ii)        Write the chemical equation occurring in the dilution chamber                  (1mk)

…………………………………………………………………………………………………………………………………………………………………………………………………….

 

iii)       Why is it necessary to pass substance Q though a purifier                           (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

]iv)      State one use of sulphuric (VI) acid              (1mk) …………………………………………………………………………………………………

5. (a) The diagram below represents a set-up that was used to obtain dry nitrogen from air. Study it and answer the questions that follow.

 

 

 

 

(i) Name solid Q.                   (1mk)

………………………………………………………………………………………………

(ii) What is the purpose of sodium hydroxide ? (1mk)

…………………………………………………………………………………………………

(iii) Write an equation for the reaction which took place in tube P.                        (1mk)

………………………………………………………………………………………………

………………………………………………………………………………………………

(iv) Give the name of one impurity in the nitrogen gas obtained.                (1mk)

…………………………………………………………………………………………………

(v) Why is liquid nitrogen used for storage of semen for artificial insemination? (1mk)

………………………………………………………………………………………………

 

(b) The set-up below was used to prepare nitric acid.

 

 

1. Give the name of liquid R.(1mk)

………………………………………………………………………………………………

1. Write an equation for the reaction which took place in the retort flask. (1mk) …………………………………………………………………………………………………

…………………………………………………………………………………………………

 

III. Explain why: –

(a) Nitric acid is not stored in clear/transparent glass. (2mks)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

(b) The reaction between copper metal with 50% nitric acid (one volume of acid added to an

equal volume of water) in an open test tube produces brown fumes. (2mks)

…………………………………………………………………………………………………

…………………………………………………………………………………………………

 

 

 

 

 

 

6. The flow chart below shows some reactions starting with copper (II) nitrate. Study it and answer questions that follow.

 

1. i) State the condition necessary in step 1                                 (1mk)

………………………………………………………………………………………………….

 

1. ii) Identify: (4mks)

Reagent M

…………………………………………………………………………………………………..

Gas S

…………………………………………………………………………………………………..

Acidic products  T

………………………………………………………………………………………………….

V

…………………………………………………………………………………………………..

iii)       Write the formula of the complex ion formed in step 3.                              (1mk)

…………………………………………………………………………………………………………………………………………………………………………………………………….

 

 

1. iv) Write the equations for the reaction in   (2 mks)

Step 1

………………………………………………………………………………………………

Step 2

…………………………………………………………………………………………………

 

7. The flow chart below shows industrial manufacture of sodium carbonate. Study it and answer the questions that follow.

 

(a)        Name substances A, B, C and D.                                                           (4mks)

A

……………………………………………………………………………………………….. B

………………………………………………………………………………………………..

 

 C

………………………………………………………………………………………………………….

 

D

……………………………………………………………………………………………………………

 

(b)        Write equation for the reactions taking place in chamber 2, 3 and 5.      (3mks)

Chamber 3

…………………………………………………………………………………………………………………………………………………………………………………………………………………………

Chamber 5

………………………………………………………………………………………………………………………………………………………………………………………………………………………..

Chamber 2

…………………………………………………………………………………………………………………………………………………………………………………………………………………………

 

 

(c)        Name the physical process in chamber 4 and 5.                                      (2mks)

Chamber 4

……………………………………………………………………………………………………………

 

Chamber 5

……………………………………………………………………………………………………………

(d)       Name one source of carbon (IV) oxide for Solvay process.             (1mk)

……………………………………………………………………………………………………………………………………………………………………………………………………

 

(f)       give 2 uses of sodium carbonate                        (1mk)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

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