🌊PAPER 41-Qns

 

THE PRESIDENT’S OFFICE

MINISTRY OF EDUCATION, REGIONAL ADMINISTRATION AND LOCAL

GOVERNMENT

O-STUDY LIBRARY

CHEMISTRY MIDTERM EXAMINATION

FORM THREE- AUGUST 2023.

Time: 3Hours

INSTRUCTIONS.

1. This paper consists of section A, B and C with a total of 14 questions

2. Answer all questions in section A and B and ONE (1) question from section C

3. Section A and C carries 15 marks, while section B 70 marks

4. Cellular phones and any unauthorized materials are not allowed in the examination room.

5. Non programmable calculators may be used.

6. Write your name on every page of your answer booklet

7. Where necessary the following constants may be used;

• Atomic masses; H=1, C=12, N=14,O=16, Na=23, S,=32, Ca =40, Cl =35.5, Cu=64,Zn=65.

• Avogadro’s number = 6.02 x 10²³

• GMV at s.t.p = 22.4dm³

• 1 faraday = 96,500 coulombs.

• Standard temperature = 273K

• Standard pressure = 760mmHg.

• 1 Litre = 1 dm³= 1000cm³

SECTION A (20 Marks)

Answer All questions in this section.

1. For each of the items (i)-(xv), choose the correct answer from among the given alternatives and write its letter beside the item number in the answer booklet provided.

(i) 1.4 g of potassium hydroxide is dissolved in water to form 250 cm³ of solution. What is the molarity of this solution?

1. 0.01 M

2. 0.1 M

3. 1.4 M

4. 5.6 M

5. 6.0 M

(ii) In the blast furnace carbon monoxide is prepared by passing carbon dioxide over a red¬hot coke. Carbon dioxide is

1. an accelerator

2. an oxidizing agent

3. a reducing agent

4. a catalyst

5. oxidized.

(iii) A catalyst can be described as a substance…

1. that alters the rate of reaction

2. that slows down the rate of reaction

3. used in every reaction so as to speed up rate of reaction

4. that starts and speeds up the rate of reaction

5. that terminates the chemical reaction.

(iv) A covalent bond is formed when…

1. a metal combines with a non¬metal

2. potassium and oxygen combine

3. ammonia is formed

4. two metals combine

5. an atom loses an electron.

(v) A solvent can be obtained from a solution by

1. evaporation followed by decantation

2. filtration and condensation

3. evaporation and filtration

4. evaporation and condensation

5. crystallization followed by sublimation.

(vi) Aqueous sugar solution is a poor conductor of electricity because

1. water and sugar are covalent compounds

2. water is a non¬electrolyte

3. sugar is a non¬electrolyte

4. sugar is covalent when in liquid form

5. sugar dissolves completely in water.

(vii) Fractional distillation process of a mixture of water and ethanol is possible because

1. water and ethanol have the same boiling point

2. water has lower boiling point than ethanol

3. ethanol has lower boiling point than water

4. water and ethanol form partially immiscible liquid solution

5. water and ethanol are immiscible liquids.

(viii) What will be the molarity of a solution which contains 26.5 g of anhydrous sodium carbonate in 5 dm³ of solution?

1. 0.05 M

2. 0.25 M

3. 5.30 M

4. 0.025 M

5. 0.50 M

(ix) 0.69g of sodium is equivalent to_______moles of sodium.

1. 0.13

2. 3

3. 0.3

4. 0.03

5. 0.003

(x) What mass of solid potassium chloride is needed to prepare 250cm³ of 0.235M solution? (K=39,Cl=35.5).

1. 9.23g

2. 31.3g

3. 15.6g

4. 4.83g

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

2. Match the items in LIST A with the responses in LIST B by writing the letter of the correct response beside the item number in the answer booklet provided.

LIST A	LIST B
A gas that explodes when flame is applied in the presence of air. element with atomic number 40. A gas prepared in a laboratory by the isolation of air. An element with electronic configuration of 2:8 An element used in making jewelers.	Mercury Diamond Hydrogen Zinc Sodium Calcium. Neon Argon Nitrogen.

LIST A	i	ii	iii	iv	v
LIST B

SECTION B (70 Marks)

Answer all questions in this section.

3. Hydrogen gas can be prepared by passing steam over heated magnesium ribbon as shown in the figure 2.

1. Write an equation for the reaction that produces hydrogen gas.

2. Explain why the delivery tube must be removed from beneath the water before heating is stopped.

3. Explain why sodium metal is not suitable for this experiment.

4. A solution contains 40.3g of substance XOH per litre .250.0cm³ of this solution required 30.0cm³ of 0.3M sulphuric(VI)acid for complete neutralization.

1. Calculate the number of moles of XOH that reacted.

2. Determine the relative atomic mass of X.

5. (a) Explain the following observations

1. A piece of iron bar is coated with a brown substance when left in the open on a rainy day.

2. at a certain experiment of sodium thiosulfate against time, when solution was added at 30cm³ and zero amount of water time recorded was 2sec after cross to disappear, and then solution measured about 20cm³ mixed with 10cm³ of water time recorded after cross to disappear was 48sec. Explain why.

6. 30.0 cm3 of aqueous sodium hydroxide containing 8.0 g per litre of sodium hydroxide were completely neutralized by 0.294 g of a dibasic acid(H₂SO₄).Determine the relative molecular mass of the dibasic acid. (Na = 23.0 ; O = 16.0; H 1.0)

7. Element U has atomic number 12 while element V has atomic number 16.How do the melting points of their oxides compare? Explain.

(8.) You are provided with a compound composed of 22.2% zinc, 11.6% sulphur, 22.3% oxygen, and the rest percentage is water of crystallization.Calculate the molecular formula of the compound if its molecular mass is 283.

9. (a.) Name the compound which causes temporary hardness of water and the compound which causes permanent hardness of water.

(b) Write one balanced chemical equation in each case to show how to remove temporary and permanent hardness of water.

10.(a) Giving three reasons, explain why air is said to be a mixture of gases.

(b) (i) People suffering from heartburn usually use wood ashes for relief.Mention characteristic which makes the ashes to be used for heartburn relief.

(ii)Give four compounds found in laboratories which show the same characteristics as ashes.

SECTION C (15 Marks).

11). Read the following information carefully then answer questions that follow: 25 cm³ of potassium hydroxide were placed in a flask and a few drops of phenolphthalein indicator were added. Dilute hydrochloric acid was added until the indicator changed colour. It was found that 21 cm³ of acid was used.

1. (i) What piece of apparatus should be used to accurately measure out 25cm³ of sodium hydroxide solution?

(ii) What colour was the solution in the flask at the start of the titration?

(iii) What colour did it turn when the alkali had been neutralized?

2. (i) Was the acid more concentrated or less concentrated than the alkali?Give reasons for your answer.

(ii) Name the salt formed in the neutralization.

(iii) Write an equation for the reaction.

3. Utilizing the given information describes how you can obtain pure crystals of the salt.

 

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