🌊PAPER 52-Qns

 

O-STUDY LIBRARY

FORM THREE MIDTERM TEST

CODE: 032/1 CHEMISTRY 1

TIME: 2:30 HOURS September 2021

INSTRUCTIONS

1. This paper consists of three sections A,B and C

2. Answer all questions from section A and B

3. Write your index number on every page of your answer sheet.

4. You may use the following constants where necessary

• 1litre = 1dm³ = 1000cm³

• 1Faraday = 96500 C.

• Avogadro’s number = 6.02 x 10 ²³

• GMV at STP = 22.4dm³.

• R.A.M: Na = 23, H =1, C = 12, N= 14, O = 16, Mg = 24,Cl= 35.5, Ca=40,

Fe = 56, Cu = 64, Zn = 65, Pb = 207, Ag = 108, S = 32.

SECTION A(15 marks)

1. Choose the most correct answer amongst the four alternatives given in each item (i – x).

1. The substance was found to have 3.0 P^H; this means;-

1. The substance was neither acidic or basic

2. The substance was very acidic

3. The substance was very basic

4. The substance was neutral

2. The following are the ions that cause hardness of water;-

1. Mg²⁺, Ca²⁺,

2. Mg²⁺, ,

3. Ca²⁺, ,

4. K⁺, Mg²⁺,

3. Hydrogen gas is not prepared industrially by fractional distillation of a liquefied air, because;-

1. It is does not freeze there difficult to liquefy

2. It is the most available element with 70% by mass

3. It is not among the components in air

4. It can be prepared by acids and water

4. The mass of Magnesium oxide with 0.0286 moles is;-

1. 1.14g

2. 0.00072g

3. 1398.6g

4. 11.44g

5. Which of the following compounds cannot form a molten liquid when heated?

1. Ammonium Chloride

2. Calcium Chloride

3. Cobalt Chloride

4. Copper (II) sulphate

6. The electronic configuration of O^–2 is;-

1. 2:6

2. 2: ^–2

3. 2:8

4. 2:4

7. The morality of Calcium hydroxide of 6.8g dissolved in 250cm³ solution is;-

1. 0.1M

2. 0.0365M

3. 0.05M

4. 0.367M

8. Iron rusting is said to be chemical change because;-

1. Its chemical properties are the same mixing air and water

2. The change is quite reversible

3. The change is irreversible

4. It dissolves in water and air

9. Most of salts have comparatively high melting points because they have;-

1. Crystalline structure

2. Low pressures

3. High specific heats

4. Strong electronic attraction between ions

10. A hen’s egg shell contain Calcium;-

1. Sulphate

2. Carbonate

3. Chlorate

4. Nitrate

Qns	i	ii	iii	iv	v	vi	vii	viii	ix	x
Ans

2. Match the items in LIST A with those in LIST B and write your answers beside the item number number in your answer sheets

LIST A	LIST B
Amphoteric oxide Acidic oxide Basic oxide Neutral oxide Efflorescent	CO CaO CO2 PbO Na2CO3 Na2CO3.10 H2O

LIST A	i	ii	iii	iv	v
LIST B

SECTION B (70 Marks)

Answer all question in this section

3. (a) Classify the following reactions into oxidation and reduction.

1. S(s) + O₂(g) SO_2(g).

2. N₂(g) +3H₂(g) 2NH₃(g)

3. Fe²⁺(aq) Fe³⁺(aq)+e^-

4. Fe³⁺(aq)+e^- Fe²⁺(aq).

(b) What is the oxidation number of iron in iron (III) chloride. Show clearly how you arrived at your answer.

(c) In the following reaction, name reducing agent and oxidizing agent and give evidence to support your answers.

CuO(s)+H₂(g) Cu(s) +H₂O(l)

4. (a) The body of a ship painted to prevent rusting

1. How does paint stop rusting?

2. Why might a ship in sea water rust faster than the one that is only used in freshwater?

3. Explain how oxygen gas influence rusting

(b)(i) Give two (02) similarities between rusting and combustion.

(ii) State two(02) application of combustion at home and your school environment.

5. (a) Hydroxide of metal Y reacts with hydrochloric acid as shown in the chemical equation below.

Y(OH)₂+ 2HCl(aq) YCl₂(aq) +H₂O(l).If it was found that 5.8g of Y(OH)₂ reacted with 0.2MHCl. Calculate the

9. Molar mass of Y(OH)₂

_{(ii )} Atomic number of Y.

(b) State three differences between bonds found in CO₂ and MgO.

6. (a) State Faraday’s laws of electrolysis.

(b) i. Name the reaction that occurs at cathode and anode.

ii. What mass of zinc will be formed in electrolysis of zinc sulphate when 15 amperes of electricity pass through electrolysis for one and half hours.

iii. Draw electrolytic cells for purification of impure copper.

7. (a) i. Explain two (02) ways by which hydrogen gas is manufactured on a large scale.

ii. State four industrial uses of hydrogen gas.

(b) Oxygen and nitrogen are obtained from air by fractional distillation. Explain why this method can be used for this purpose yet it can not be used to obtain hydrogen and oxygen from water.

8. (a) Analysis of an organic compound showed 2.84g of carbon combined with 0.47 g of hydrogen and 3.79 g of oxygen. If the half of its vapour density is 15

1. What is the empirical formula of this organic compound?

2. What is the molecular formula of this organic compound?

(b) state any three (3) ways of minimizing accidents in chemistry laboratory

9. (a) Calculate the oxidation number of the following elements in the bracket

1. H₂SO₄ (S)

2. Cr₂O₇^2- (Cr)

3. NH₄⁺ (N )

(b) The following are some elements found in the periodic table, A, B,C and E with atomic numbers 1,2,3,4,11 and 17 respectively.

(i) For each atomic number, write the symbol of each element.

(ii) Write equation which represent reaction between the elements with atomic number 11 and 17

(iii)Write the name of an inert gas element represented by the given atomic numbers.

10 (a) Student X from Lyamungo secondary school asked Mwajuma Mrisho, a form Three student during chemistry club which always commences at 7:00pm that “why is the knowledge about strength of acids and bases important in acid base titration”?. Assume you were there during that evening chemistry session and Mwajuma didn’t know the answer to the question. As a chemistry student, how could you tell student X ?

(b) Suggest a suitable indicator for titrations.

i. Hydrochloric acid against ammonia solution.

ii. Sulphuric acid against sodium hydroxide.

iii. Ethanoic acid against potassium hydroxide.

(c) i. Why do chemistry laboratory exits open outward?

ii. What are the criteria that you will consider if you want to tell that a certain substance is a suitable catalyst for a given reaction? Give any two.

11. Give reason(s )for the following facts.

i. It is difficult to breathe in oxygen directly from the surroundings at high altitudes.

ii. It is difficult to cook ugali at high altitudes.

iii.Blue hydrous copper sulphate turns white when heated in a beaker.

4. Calcium hydroxide turns whitish when left uncovered.

5. When zinc nitrate is heated a brown colour is observed and yellow residues observed when hot and white when cold.

6. Solid CaCl₂ does not conduct electricity while its aqueous solution does.

7. Magnesium ions do have 12 electrons.

12. (a) i. Mention three advantages of biogas as a source of energy.

ii. Describe four effects of cutting down trees for firewood and charcoal.

(b) i. Explain briefly the importance of chlorination in the process of urban water treatment.

ii. Explain two different methods that can be used to treat and purify water at home.

SECTION C (15 Marks)

Answer only one question in this section

13.(a) i. List three factors affecting the selection of ions to be discharged at the electrode.

ii. A bluish copper (II) sulphate solution was electrolyzed by using carbon electrodes. Write an ionic equation for the reactions which occurred at the cathode and anode and explain what will happen to the colour of electrolyte as electrolysis continues.

(b) Explain how knowledge of the fire triangle is applied in stopping fire in the following circumstances.

i. Spraying air pressurized water on the burning paper industry.

ii. Spraying carbon dioxide to a petrol station that catches fire.

(c) Using appropriate example(s) explain seven uses of compounds in our daily life.

14. Volumetric analysis is not only concerned with calculating molar concentration, mass concentration, finding unknown relative atomic masses of element in acid or base, determination of percentage purity and water of crystallization of acids and bases on a piece of paper as what is done in secondary school and higher learning institution instead it is applied daily in different fields that work to improve people’s well being. Explain the usefulness of volumetric analysis in

(i) Medicine

(ii) industries

(iii)Analysis of water

4. Agriculture

5. (iv) Extraction of metals

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