Chemistry Paper 1 – 2023

Chemistry Paper 1 – 2023

1. The atomic numbers of nitrogen and fluorine are 7 and 9, respectively.

(a) Use electron dot (•) and cross (×) diagrams to show bonding in the molecules of:

(i) Nitrogen. (1 mark)

(ii) Fluorine. (1 mark)

(b) Based on the diagrams in (a), explain why fluorine is more reactive than nitrogen. (1
mark)

2. Salts can be classified into normal and acid salts.

(a) Name another type of salt. (1 mark)

(b)

(i) Describe how an acid salt can be prepared using 0.1 M sulphuric(VI) acid and 0.1 M
sodium hydroxide. (1 mark)

(ii) Write a balanced chemical equation for the reaction in (b)(i). (1 mark)

3. Complete Table 1 by writing the chemical formulae of the products formed when
metal nitrates are strongly heated. (3 marks)
4. The following flow diagram represents the production of sulphuric(IV) acid:

[Diagram showing sulphur, SO₂, and H₂SO₄ production in three stages]

(a) State the optimum conditions required for the reaction in Unit II. (1 mark)

(b) Stage II occurs in two steps. Describe these steps. (2 marks)

5. The following equilibrium exists in aqueous ammonia:

NH_3(aq) + H_2O(l) \rightleftharpoons NH_4^+(aq) + OH^-(aq)

(a) Using this equilibrium, explain why ammonia is classified as a weak base. (1 mark)

(b) When aqueous ammonia is added dropwise to a solution of copper(II) sulphate, a blue
precipitate forms. The precipitate then dissolves, forming a deep blue solution. Write the
chemical formula of the substance responsible for:

(i) The blue precipitate. (1 mark)

(ii) The deep blue solution. (1 mark)

6. The molecular formula of two straight-chain hydrocarbons is C₄H₆.

(a) Write the general formula of the homologous series to which these hydrocarbons
belong. (1 mark)

(b) Draw the structural formulas of the two hydrocarbons and provide their names. (2
marks)

7. At high temperature, hydrogen and oxygen react according to the equation:

O_2(g) + 2H_2(g) \rightarrow 2H_2O(g)

In an experiment, a mixture containing 200 cm³ of oxygen and 300 cm³ of hydrogen was
heated to form water.

(a) Identify the gas that was in excess and determine by how much. (1 mark)

(b) Calculate the volume of water vapor formed. (1 mark)

(c) Describe how one could confirm that the product obtained was pure water. (1 mark)

8. Silk and rubber are examples of natural polymers.

(a) Name another natural polymer. (1 mark)

(b) State the sources of:

(i) Silk. (1 mark)

(ii) Natural rubber. (1 mark)

9. The following setup was used to investigate rusting of iron over one week:

[Diagram showing test tubes with nails in different conditions: air, tap water, boiled water
with oil, and salt solution]

(a) Write the chemical formula of the compound commonly referred to as rust. (1 mark)

(b) Explain why:

(i) No rusting occurred in test tube III. (1 mark)

(ii) Select the test tube in which the highest amount of rust was observed. Give a reason. (1
mark)

10. Avogadro’s constant is mol^{-1}.

(a) Calculate the total number of ions present in 500 cm³ of 2.0 M calcium nitrate solution.
(2 marks)

(b) Explain why the electrical conductivity of 2.0 M calcium nitrate is higher than that of 2.0
M potassium nitrate. (1 mark)
11. Carbon(IV) oxide and methane are gases found in the atmosphere.

(a) State one disadvantage of carbon(IV) oxide in the atmosphere. (1 mark)

(b) Name one source of methane emissions into the atmosphere. (1 mark)

(c) Suggest a method to reduce carbon(IV) oxide emissions into the atmosphere. (1 mark)

12. A sample of a chloride of element D was found to contain 5.70 g of the compound, with
4.55 g being chlorine.

(a) Determine the empirical formula of the chloride given that D = 27.0 and Cl = 35.5. (2
marks)

(b) Given that the relative formula mass of the chloride is 267, determine its molecular
formula. (1 mark)

13. Table 2 shows the boiling points of ethane, butane, and ethanol.

Table 2

(a) Explain why the boiling point of butane is higher than that of ethane. (1½ marks)

(b) Explain why the boiling point of ethanol is higher than that of butane. (1½ marks)

14. Small pieces of beryllium, magnesium, and calcium were placed in test tubes containing
cold distilled water mixed with phenolphthalein indicator, as shown in Figure 5.

Figure 5 (Shows three test tubes labeled I, II, and III, containing beryllium, magnesium, and
calcium, respectively.)

State and explain the observations made in each of the following test tubes:

Test tube I (1 mark)

Test tube II (1 mark)

Test tube III (1 mark)

15. Element A has a mass number of 40 and 21 neutrons.

(a) Write the electron arrangement of element A. (1 mark)

(b) Give the formula of the compound formed when element A reacts with sulfur.
(S = 16.0) (1 mark)

16. Study the setup in Figure 1 and answer the questions that follow.

(Figure 1 shows a burning candle, a funnel, a U-tube containing solid B, ice, and a test tube
with calcium hydroxide solution.)
(a) At the end of the experiment, solid B changed from white to blue. Explain. (1 mark)

(b) The other product of the burning candle formed a white precipitate with the calcium
hydroxide solution. Write an equation for the reaction. (1 mark)

(c) State the role of apparatus C. (1 mark)

17. (a) State and explain the factors that are considered when collecting a gas by
displacement of:

(i) Air (1 mark)

(ii) State and explain the factors considered when collecting a gas by displacement of:

Water (1 mark)

(b) Other than collecting a gas by displacement of air or water, state another method that
can be used to collect a gas. (1 mark)

18. (a) Carbon(II) oxide was passed over 4.1 g of heated copper(II) oxide in a combustion
tube until there was no further change. The mass of the final substance was found to be 3.29
g. Complete Table 1 and determine the empirical formula of the oxide.

(Given: Cu = 64.0; O = 16.0)

Table 1

Empirical formula: …………………………………………. (2 marks)

(b) State the property of carbon(II) oxide that was demonstrated in the experiment. (1
mark)

19. (a) Draw the structural formula of 2-methylbut-2-ene. (1 mark)

(b) Bromine water was added to 2-methylbut-2-ene.

(i) State the observation made. (1 mark)
(ii) Name the type of reaction that took place. (1 mark)

20. Table 2 shows the pH values of solutions of compounds D, E, F, and G.

(a) State which one of the compounds is likely to be:

(i) Sodium chloride (½ mark)
(ii) Ammonium nitrate (½ mark)

(b) Select two compounds that can be used to illustrate the amphoteric nature of an oxide.
(1 mark)

(c) Give a reason for your answer in (b). (1 mark)

21. (a) State the difference between a covalent bond and a dative covalent bond. (1 mark)
(b) Using dots (•) and crosses (×) to represent electrons, draw a diagram to show the
bonding in ammonia (NH₃). (1 mark)

(c) Using the diagram in (b), state one property that makes ammonia react with hydrogen
ions (H⁺). (1 mark)

22. Figure 2 shows a reaction scheme starting with copper turnings. Study it and answer the
questions that follow.

Diagram Explanation (Figure 2):

Step 1: Copper turnings heated → Blue solution

Step 2: Blue solution + Aqueous K₂Cr₂O₇ / H⁺ → Green solution + Gas H

Step 3: Blue solution + Excess NH₃(aq) → Solution J

(a) State the reagent that is added in Step 1. (1 mark)

(b) Identify Gas H. (1 mark)

(c) Write the formula of the complex ion in Solution J. (1 mark)

23. Study the information in Table 3 and answer the questions that follow.
The elements belong to the same chemical family.
(The letters are not actual symbols of the elements).

(a) Classify the elements as either metals or non-metals. Give a reason. (1 mark)

(b) (i) Identify the element which is:

Least reactive: ...................................................... (½ mark)

Most reactive: ...................................................... (½ mark)

(ii) Give a reason for the answer in (b)(i). (1 mark)

24. Nitrogen(IV) oxide is prepared by heating lead(II) nitrate.

(a) Write an equation for the reaction. (1 mark)

(b) At room temperature, nitrogen(IV) oxide (NO₂) exists in equilibrium with dinitrogen
tetroxide (N₂O₄):

2NO_2(g) \rightleftharpoons N_2O_4(g) \quad \Delta H = \text{negative}

(Color: NO₂ is brown, N₂O₄ is pale yellow)

State the observation made when the mixture is placed in an ice bath. Give a reason. (2
marks)
25. A monomer has the following structure:

\text{CH} = \text{CH}_2

\quad |

\quad \text{C}_2\text{H}_5

(a) Draw the structure of its polymer containing three monomer units. (1 mark)

(b) A sample of the polymer formed from this monomer has a molecular mass of 4992.
Determine the number of monomer units in the polymer.
(Atomic masses: C = 12, H = 1.0) (2 marks)

26. Hydrogen gas can be prepared by passing steam over heated magnesium ribbon, as
illustrated in Figure 2.

(a) Write the balanced chemical equation for the reaction that produces hydrogen gas. (1
mark)

(b) Explain why the delivery tube must be removed from the water before stopping the
heating process. (1 mark)

27. A farmer intended to plant cabbages on his farm. He first tested the pH of the soil and
found it to be 3.0. If cabbages grow best in alkaline soils, explain the advice that should be
given to the farmer to ensure a high yield. (2 marks)

28. A solution contains 40.3 g of substance XOH per litre. 25.0 cm³ of this solution required
30.0 cm³ of 0.3 M sulphuric(VI) acid for complete neutralisation.

(a) Calculate the number of moles of XOH that reacted. (½ mark)

(b) Determine the relative atomic mass of X. (1½ marks)

29. Table 1 shows the properties of two chlorides, D and E.

(a) State the type of bond present in:

(i) D ________________________________ (1 mark)
(ii) E ________________________________ (1 mark)

30. Sulphur(IV) oxide is prepared in the laboratory using the set-up in Figure 3. Study it and
answer the questions that follow.

(a) Identify substance F. (1 mark)

(b) Write an equation for the reaction that takes place in the flask. (1 mark)

(c) State the purpose of liquid G. (1 mark)

31. The graph in Figure 4 was obtained when a certain substance was heated, and its
temperature was recorded at regular intervals.

[Graph

32. Ethene is prepared in the laboratory by dehydration of ethanol.

(a) Name a suitable dehydrating agent used in this process. (1 mark)

(b) State the condition necessary for the reaction to occur. (1 mark)

(c) Write an equation for the dehydration process. (1 mark)

33. A boiling tube filled with chlorine water was inverted in a trough containing the same
solution and left in sunlight for about 2 hours.

(a) State the observations made in the boiling tube. (1 mark)

(b) Explain the observations made in (a). (1 mark)

(c) Write an equation for the reaction that occurred in the boiling tube. (1 mark)

34. 5 g of calcium carbonate was strongly heated to a constant mass. Calculate the mass of
the solid residue formed.
(Atomic masses: Ca = 40.0, C = 12.0, O = 16.0) (2 marks)

35. During the laboratory preparation of oxygen, manganese(IV) oxide is added to reagent
H.

(a) Name reagent H. (1 mark)

36. Figure 5 shows an apparatus used to separate a mixture of water and hexene.

(a) Name the apparatus in Figure 5. (1 mark)

(b) State the principle by which the mixture of the two liquids is separated. (1 mark)

(c) Identify the liquids R and S if the density of hexene is 0.66 g/cm³.
(i) R: .......................................... (½ mark)
(ii) S: .......................................... (½ mark)