CHEMISTRY TOPICAL QUESTIONS AND ANSWERS

The following set – up was made in an experiment by a group of form four students. The readings of the balance before and after experiment were indicated in the diagram below.

14/10/2021

The following set – up was made in an experiment by a group of form four students. The readings of the balance before and after experiment were indicated in the diagram below. Given that the initial temperature of water was 26.7 degrees centigrade respectively. The specific heat capacity of water is 4200Jkg-1k-1

Determine:

a) Temperature change that occurred (1mk)

b) Amount of ethanol used (1mk)

10.5 – 1.0 = 9.5g

c) Moles of ethanol used (2mks)

d) Amount of heat gained by water (2mks)

e) Molar enthalpy of combustion of ethanol (2mks)

f) Use the following thermochemical processes to answer the questions that follow;

​Determine:

​a) Temperature change that occurred (1mk)

​b) Amount of ethanol used (1mk)

​c) Moles of ethanol used (2mks)

​d) Amount of heat gained by water (2mks)

​e) Molar enthalpy of combustion of ethanol (2mks)

​f) Use the following thermochemical processes to answer the questions that follow;

​i) Draw an energy level diagram representing the formation and combustion processes of propane, carbon and hydrogen (2mks)

​ii) Hence or otherwise, determine the heat of formation of propane (2mks)

a) On the grid provided, plot on the same axis, the graph of volume of gas produced against time (4mks)

​b) From the graph, determine the rate of reaction of both acids at 55 seconds

​i) 1M sulphuric (VI) acid (1mk)

​ii) 1M ethanoic acid (1mk)

c) The rate of reaction of H2SO4 is twice that of ethanoic acids. This is because H2SO4 is stronger while ethanoic acid is a weak acid.

​c) Explain the difference in the rate of evolution of the gas as determined in (b) above (2mks)

d) Calculate the number of moles of hydrogen gas produced when 10cm magnesium ribbon is completely reacted with 1M sulphuric (VI) acid. (Molar gas volume = 24dm3 at r.t.p) (2mks)

​e) What mass of magnesium had therefore reacted? (Mg = 24) (2mks)

​a) Name the substance the anode is made of (1mk)

​b) Explain your answer in (a) above (1mk)

​c) What is the role of the diaphragm in Down’s cell (1mk)

d) In Down’s cell for the manufacture of Sodium metal, Calcium chloride salt is added to lower the melting point from 8000C to 6000C. Explain why it is necessary to lower the melting point (1mk)

​e) Calculate the mass of sodium metal produced if a current of 50 amperes is passed through the molten Sodium chloride for two (2) hours (Na = 23, F = 96500C) (2mks)

​f) Below is a list of potential differences obtained when metal P, Q, R, S and T are used in the following electrochemical cell Metal (s) / Metal ions // Copper (II) ions / copper (s)

​i) Which metal is likely to be Copper. Explain (2mks)

​ii) Identify the strongest reducing agent (1mk)

​iii) Which two half – cells would be combined to produce the highest voltage? (1mk)

​iv) Give a cell representation of the cell in F (iii) above. (2mks)

The empirical formula of a hydrocarbon is (CH2). It has a density of 0.001167g/cm3 at room temperature and pressure. (Molar gas volume at r.t.p is 24dm3)

​a) Determine the molecular formula of the hydrocarbon (3mks)

b) Draw the structural formula of the hydrocarbon (1mk)

​c) Ethene gas burns in Oxygen to form Carbon (IV) oxide and water.

​i) Write an equation for the reaction between ethane gas oxygen gas (1mk)

ii) 15cm3 of ethene gas were mixed with 50cm3 of oxygen gas and the mixture was ignited into complete combustion. Calculate the volume of excess unreacted gas (3mks)

​d) What happens when ethene gas is bubbled through bromine water? (2mks)

​e) Give any two uses of ethene gas (2mks)

​​a) Name;

​i) Substance V (1mk)

​ii) Solid X (1mk)

​b) Write an equation for the preparation of hydrogen sulphide (1mk)

​c) What property of the gas enables it to be collected by the method shown in the diagram? (1mk)

​d) What is the purpose of the water in the second flask? (1mk)

​e) What precaution should be taken when preparing the gas? (1mk)

​f) Explain the observations made when dry hydrogen sulphide is exposed to wet Lead (II) acetate paper (2mks)

​g) State the observation that would be made when hydrogen sulphide gas is bubbled through acidified Potassium dichromate (VI) solution (1mk)

​h) Explain why it is not advisable to dispose off hydrogen sulphide gas by burning (1mk)

​a) i) Are the members in this group likely to be conductor or non – conductors? (1mk)

ii) Which element would have the lowest atomic number? Explain. (1mk)

​b) The grid below represents part of the periodic table. Study it and answer the questions that follow. (The letters are not the actual symbols of the elements)

​i) Select the element in period three which has the shortest atomic radius. Give a reason for your answer. (2mks)

​ii) Using dots (•) and crosses (x) to represent outermost electrons, draw a diagram to show the bonding in the compound formed when chlorine reacts with element X (1mk)

​iii) When three liters of chlorine gas were completely reacted with element Y, 11.85g of the product were formed. Calculate the relative atomic mass of element Y. (3mks)

​​a) Name the following;

​i) Gas L (1mk)

​ii) Gas H (1mk)

​iii) K (1mk)

​​b) Name the processes involved in the following steps

​i) Step I (1mk)

​ii) Step II (1mk)

​​iii) Step III (1mk)

​c) Draw the structure of compound E (1mk)

​d) Write a chemical equation for the complete combustion of substance F (1mk)

​e) Name the condition and reagents in step III

​i) Condition (1mk)

​ii) Reagent (1mk)

​f) Calculate the mass of salt Q that would be formed by using 21.9kg of G when it reacts with excess sodium hydroxide (2mks) (C = 120, H = 1.0, Na = 23.0, O = 16.0)

​g) i) Draw the structure of polymer D (1mk)

​ii) State one use of the above polymer (1mk)

​Differentiate between empirical and molecular formula (2mks)

​Use the information below to answer the questions that follow Ethanol is formed as shown below

​Draw the energy cycle diagram and for the formation and combustion of ethanol and calculate the heat of formation of ethanol (3mks)

A volume of 80cm3 of a mixture of propane (C3H8) and oxygen were ignited in an experiment. The products were cooled and passed through an aqueous sodium hydroxide. The final volume was reduced by 30cm3

a) Write the equation for the combustion of propane (1mk)

b) Determine the volume of;

i) The component of the original mixture (2mks)

ii) Residual oxygen (1mk)

​a) State three differences between chemical and nuclear reactions. (3mks)

Chemical reaction

Nuclear reaction

b) Study the figure below and answer the questions that follow

Identify the radiations A, B and C (3mks)

Determine:

a) Temperature change that occurred (1mk)

b) Amount of ethanol used (1mk)

c) Moles of ethanol used (2mks)

d) Amount of heat gained by water (2mks)

e) Molar enthalpy of combustion of ethanol (2mks)

f) Use the following thermochemical processes to answer the questions that follow;

i) Draw an energy level diagram representing the formation and combustion processes of propane, carbon and hydrogen (2mks)

ii) Hence or otherwise, determine the heat of formation of propane (2mks)

b) From the graph, determine the rate of reaction of both acids at 55 seconds

i) 1M sulphuric (VI) acid (1mk)

ii) 1M ethanoic acid (1mk)

c) The rate of reaction of H₂SO₄ is twice that of ethanoic acids. This is because H₂SO₄ is stronger while ethanoic acid is a weak acid.

c) Explain the difference in the rate of evolution of the gas as determined in (b) above (2mks)

d) Calculate the number of moles of hydrogen gas produced when 10cm magnesium ribbon is completely reacted with 1M sulphuric (VI) acid. (Molar gas volume = 24dm³ at r.t.p) (2mks)

e) What mass of magnesium had therefore reacted? (Mg = 24) (2mks)

a) Name the substance the anode is made of (1mk)

b) Explain your answer in (a) above (1mk)

c) What is the role of the diaphragm in Down’s cell (1mk)

d) In Down’s cell for the manufacture of Sodium metal, Calcium chloride salt is added to lower the melting point from 800⁰C to 600⁰C. Explain why it is necessary to lower the melting point (1mk)

e) Calculate the mass of sodium metal produced if a current of 50 amperes is passed through the molten Sodium chloride for two (2) hours (Na = 23, F = 96500C) (2mks)

f) Below is a list of potential differences obtained when metal P, Q, R, S and T are used in the following electrochemical cell
Metal (s) / Metal ions // Copper (II) ions / copper (s)

i) Which metal is likely to be Copper. Explain (2mks)

ii) Identify the strongest reducing agent (1mk)

iii) Which two half – cells would be combined to produce the highest voltage? (1mk)

iv) Give a cell representation of the cell in F (iii) above. (2mks)

The empirical formula of a hydrocarbon is (CH₂). It has a density of 0.001167g/cm³ at room temperature and pressure. (Molar gas volume at r.t.p is 24dm³)

a) Determine the molecular formula of the hydrocarbon (3mks)

c) Ethene gas burns in Oxygen to form Carbon (IV) oxide and water.

i) Write an equation for the reaction between ethane gas oxygen gas (1mk)

ii) 15cm³ of ethene gas were mixed with 50cm3 of oxygen gas and the mixture was ignited into complete combustion. Calculate the volume of excess unreacted gas (3mks)

d) What happens when ethene gas is bubbled through bromine water? (2mks)

e) Give any two uses of ethene gas (2mks)

a) Name;

i) Substance V (1mk)

ii) Solid X (1mk)

b) Write an equation for the preparation of hydrogen sulphide (1mk)

c) What property of the gas enables it to be collected by the method shown in the diagram? (1mk)

d) What is the purpose of the water in the second flask? (1mk)

e) What precaution should be taken when preparing the gas? (1mk)

f) Explain the observations made when dry hydrogen sulphide is exposed to wet Lead (II) acetate paper (2mks)

g) State the observation that would be made when hydrogen sulphide gas is bubbled through acidified Potassium dichromate (VI) solution (1mk)

h) Explain why it is not advisable to dispose off hydrogen sulphide gas by burning (1mk)

a) i) Are the members in this group likely to be conductor or non – conductors? (1mk)

b) The grid below represents part of the periodic table. Study it and answer the questions that follow. (The letters are not the actual symbols of the elements)

i) Select the element in period three which has the shortest atomic radius. Give a reason for your answer. (2mks)

ii) Using dots (•) and crosses (x) to represent outermost electrons, draw a diagram to show the bonding in the compound formed when chlorine reacts with element X (1mk)

iii) When three liters of chlorine gas were completely reacted with element Y, 11.85g of the product were formed. Calculate the relative atomic mass of element Y. (3mks)

a) Name the following;

i) Gas L (1mk)

ii) Gas H (1mk)

iii) K (1mk)

b) Name the processes involved in the following steps

i) Step I (1mk)

ii) Step II (1mk)

iii) Step III (1mk)

c) Draw the structure of compound E (1mk)

d) Write a chemical equation for the complete combustion of substance F (1mk)

e) Name the condition and reagents in step III

i) Condition (1mk)

ii) Reagent (1mk)

f) Calculate the mass of salt Q that would be formed by using 21.9kg of G when it reacts with excess sodium hydroxide (2mks)
(C = 120, H = 1.0, Na = 23.0, O = 16.0)

g) i) Draw the structure of polymer D (1mk)

ii) State one use of the above polymer (1mk)

Differentiate between empirical and molecular formula (2mks)

Use the information below to answer the questions that follow Ethanol is formed as shown below

Draw the energy cycle diagram and for the formation and combustion of ethanol and calculate the heat of formation of ethanol (3mks)

A volume of 80cm³ of a mixture of propane (C₃H₈) and oxygen were ignited in an experiment. The products were cooled and passed through an aqueous sodium hydroxide. The final volume was reduced by 30cm³

a) State three differences between chemical and nuclear reactions. (3mks)

RCOO – Na⁺ and RCH₂OSO₃ – Na⁺ represent two types of cleansing agents

a) Name the class of cleansing agent to which each belongs (1mk)

b) Which one of the two cleansing agents is likely to pollute the environment. Explain. (2mks)

b) Draw the structural formula of ethanoic acid (1mk)

a) Name one chief ore of copper and give its formula (2mks)

Calculate the mass of copper that would be deposited on the cathode when a steady current of one ampere flows for 20 minutes through copper (II) sulphate solution (Cu = 63.5; Faraday Constance = 96500Cmol-1) (3mks)

The cell convention for an electrochemical cell is shown below

a) Name two substances that can be used as electrolytes in the above cell (2mks)

b) Which of the electrodes is the anode? (2mks)