KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Both diamond and graphite have giant atomic structures. Explain why diamond is hard while graphite is soft.
Answer
0 Comments
answers
answer
answers
In an experiment, 2.4g of sulphur was obtained by reacting hydrogen sulphide and chorine as shown by the equation below: H2S(g) + Cl2(g) → S(s) + 2HCl(g) (a) Which of the reactants acts as a reducing agent in the above reaction? Explain. (1 mk) (b) Given that the yield of sulphur in the above reaction is 75%, calculate the number Of moles of H2S(g) used in the reaction (S=32.0)
expected response
a)
i) Iron (II) Suphide ii) Hydrogen Sulphide
b) Darker paper soaked in lead acetate
Explain how you would obtain solid carbonate from a mixture of lead carbonate and sodium carbonate powders. (3mks)
Expected Response
Dissolve in water, filter to remove lead carbonate as a residue, evaporate filter to saturation and allow to cool. Crystallization to take place. Filter the crystals and dry. Evaporate to dryness
The diagram below represents a set-up that was used to react lithium with water study it and answer the questions that follow:
Chlorine and iodine are elements in the same group in the periodic table. Chlorine gas is yellow white aqueous, iodine; I2(aq) is brown. a) What observation would be made if chlorine gas is bubbled through aqueous sodium iodide? Explain using and ionic equation. (2mks) b) Under certain conditions chlorine and iodine react to give iodine chloride, ICl3(s)- What type of bonding would you expect to exist in iodine trichloride? Explain (1mk)
expected Response
a) The energy change that takes place when one mole of the compound is formed from its constituents elements in their state
b) 3x-286 = 2x-394-(277) 858 + 788+ 277 = 11369kjmol Explain why it is not advisable to use aqueous chloride solution as the salt bridge in the electrochemical cell formed between half cells, Pb2-(aq)/pb(s) E0 = 0.13V and CU2 + (aq) + (aq)/CU2+(aq)/Cu2(s) E0=0.34V (2mks)
expected response
Sodium chloride will remove Pb from the insoluble pbC12. This affects the value of the cell voltage.
On strong heating, sodium nitrate oxygen gas. In the spaces provided below, draw a labeled diagram of a set-up that could be used for heating sodium nitrate and collecting the oxygen gas liberated. (3mks)
When a candle was brunt completely. The total mass product was found to be greater than the original mass of the candle. Explain
ANSWER
a) State how burning can be used to distinguish between ethane and ethyne.
Explain your answer. b) Draw the structural formula of the third member of the homologous series of ethyne. c) The flow chart below shows a series of reactions starting with ethanol. Study it and answer the questions that follow.
ii) Write the equation for the combustion of ethanol
iii) Explain why it is necessary to use high pressure to change gas B into the polymer iv) State one use of methane
The set – up below was used to prepare hydrogen gas
a) Complete the diagram to show how a dry sample of hydrogen gas can be collected
b) Write an equation for the reaction, which takes place when hydrogen gas burns in air. c) i)1.2 litres of hydrogen gas produced at room temperature and pressure when 3.27g of zinc was used. Determine the relative atomic mass of zinc.(Molar gas volume is 24 litres) d) State two industrial uses of hydrogen gas.
The basic raw material for extraction of aluminium is bauxite
a) Name the method that is used to extract aluminium from bauxite b) Write the chemical formula of the major component of bauxite c) i) Name two major impurities in bauxite ii) Explain how the impurities in bauxite are removed d) Cryolite is used in the extraction of aluminium from bauxite. State its function f) Aluminium is a reactive metal yet utensils made of aluminium do not corrode easily. Explain this observation
Excess marble chips (calcium carbonate ) was put in a beaker containing 100cm3 of dilute hydrochloric acid. The beaker was then placed on a balance and the total loss in mass recorded after every two minutes as shown in the table below.
a) Why was there a loss in mass?
b) Calculate the average rate of loss in mass between: i) 0 and 2 minutes ii) 6 and 8 minutes iii) Explain the difference in the average rates of reaction in (b) (i) and (ii) above c) Write the equation for the reaction which takes place in the beaker d) State three ways in which the rate of the reaction above could be increased e) The solution in the beaker was evaporated to dryness what would happen if the open beaker and its contents were left in the laboratory overnight. f) Finally some water was added to the contents of the beaker. When aqueous sodium sulphate was added to the contents of the beaker, a white precipitate was formed. i) Identify the white precipitate ii) State one use of the substance identified in (f) (i) above
i) Identify the particles emitted in steps I and III
I II ii) Write the nuclear equation for the reaction which takes place in step V The table below give the percentages of a radioactive isotope of Bismuth that remains after decaying at different times. i) On the grid provided, plot a graph of the percentage of Bismuth remaining (Vertical axis) against time.
ii) Using the graph, determine the:
I. Half – life of the Bismuth isotope II. Original mass of the Bismuth isotope given that the mass that remained after 70 minutes was 0.16g d) Give one use of radioactive isotopes in medicine
a) The diagram below is a cross- section of a dry cell. Study it and answer the questions that follow.
i) On the diagram, show with a (+) sign the positive terminal
ii) Write the equation for the reaction in which electrons are produced
iii) The zinc can is lined with ammonium chloride and zinc chloride paste. iv) Give one advantage and one disadvantage of dry cells. b) The set – up below was used to (electrolyse roller lead (II) ionide.
i) State the observation that was made at the anode during the electrolysis.
Give a reason for your answer. ii) A current of 0.5 A was passed for two hours. Calculate the mass of lead that was deposited (Pb = 1F = 9,500C) The table below gives the atomic numbers of elements W, X, Y, and Z. The letters do not represent the actual symbols of the elements. a) Which one of the elements is least reactive? Explain (1mk) b) i) Which two elements would react most vigorously with each other? (1mk) ii) Give the formula of the compound formed when the elements in b(i) react (1mk)
expected response
a) X, both energy levels are full i.e 2:8 outer energy level full/has octane structure/inert gas structure.
b) (i) W and Y (ii) YW
expected response
Increase in pressure would shift the equilibrium to the left; since in pressure favors thereaction will produce less volume of gas |
Chemistry Topics
All
Archives
December 2024
|
We Would Love to Have You Visit Soon! |
Hours24 HR Service
|
Telephone0728 450425
|
|
8-4-4 materialsLevels
Subjects
|
cbc materialsE.C.D.E
Lower Primary
Upper Primary
Lower Secondary
Upper Secondary
|
teacher support
Other Blogs
|