KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
a) Distinguish between a deliquescent and a hygroscopic substance.
b) Give one use of hygroscopic substance in the laboratory.
ANSWERS
(a)Deliquescent - a substance that absorbs water from the atmosphere and changes into a solution.
Hygroscopic — a substance that absorbs water from the atmosphere but just becomes wet. (b)drying agent.
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Iron is obtained from haematite using a blast furnace shown if figure 5 below.
a) Four raw materials are required for the production of iron. Three of these are iron oxide, hot air and limestone
Give the name of the fourth raw material b) Write an equation for the reaction in which carbon (IV) oxide is converted into carbon (II) oxide. c) Explain why the temperature in the region marked Y is higher than that of the incoming hot air. d) State one physical property of molten slag other than density that allows it to be separated from molten iron as shown in figure 5. e) One of the components of the waste gases is Nitrogen (IV) oxide describe the adverse effects it has on the environment. f) Iron from the blast furnace contains about 5% carbon i) Describe how the carbon content is reduced. ii) Why is it necessary to reduce the carbon content?
ANSWERS
(a) Coke/ coal/ Charcoal/ Carbon
(b) C(s) + CO2 (g) → 2 CO(g) (c) The reaction between coke/ coal and the hot air is highly exothermic (d) Slog is immiscible with molten iron (e) Nitrogen (iv) oxide gas forms acid rain. Which corrodes metallic materials and destroys vegetation the environment. (f) (i) By passing/ blowing oxygen into molten iron which converts carbon into carbon (iv) Oxide (ii) To increase the tensile strength/ making the iron less brittle/ making it more malleable / making it more ductile.
a) Study the table below and complete it. (W-1 and X4+ are not the actual symbols of the ions).
b) State the observation that would be made in the following tests to distinguish between:
i) Sodium and copper burning pieces of each in air. ii) Sodium and Magnesium by placing small pieces of each in cold water which contains two drops of phenolphalein. c) The atomic numbers of Na and Mg are 11 and 12 respectively. Which of the elements has a higher ionization energy? Explain. d) Naturally occurring uranium consists of three isotopes which are radioactive.
i) Which of these isotopes has the longest half-life? Give a reason
ii) Calculate the relative atomic mass of uranium
(iv)State one use of radioactive isotopes in the paper industry
ANSWERS
(b) (i) Sodium burns with a yellow flame & yellow white/ solid powder is formed while copper burn with a blue green flame & black powder/ silic is formed.
(ii) Sodium darts on the surface of water / rapid fast effervescence (fast production of bubbles; solution becomes pink immediately. Magnesium sinks in water/ slow (production of bubbles) effervescence/ solution becomes pink gradually. (c) Magnesium it has a higher nuclear charge which pulls outer electrons more strongly D gm of potassium hydroxide were dissolved in distilled water to make 100cm3 of solution. 50cm3 of the solution- required 50cm3 of 2 M nitric acid for complete neutralization. Calculate the mass D, of potassium hydroxide (KOH)(aq) + HNO3(aq) →KNO3 (aq) + H2O (I) Relative formula mass of KOH = 56
State the observation that would be made when a piece of sodium metal is placed in samples of:
Pentane: __________ Pentanol: __________
The table below shows the solubility of a salt at various temperatures
What would happen if a sample of a saturated solution of the salt at 400C is heated to 800C. Explain
Write the formula of sulphide of an element C, whose atomic number is 5. (C is not the actual symbol of the element)
What type of bond is formed when lithium and Fluorine react? Explain
(Atomic numbers: Li = 3 and F = 9)
(a)Figure 3 show the changes that take place between states of matter. Some of them have been identified and others labelled.
i) Give the names of the processes
I H II G ii) Name one substance that can undergo process F when left in an open container in the laboratory. iii) The process J is called deposition. Using water as an example, write an equation that represents the process of deposition. b) Figure 4 shows the beating curve for water.
i) Give the names of the intermolecular forces of attraction in the segments;
I MN II RS ii) The heats of fusion and vaporization of water are 334.4 Jg-1 and 1159.4 Jg-1 respectively. I Explain why there is a big difference between the two. II How is the difference reflected in the curve? c) Coal, oil and natural gas are major sources of energy. They are known as fossil fuels. Hydrogen is also a source of energy. i) State and explain two reasons why hydrogen is a very attractive fuel compared to fossils. ii) State one disadvantage of using hydrogen fuel instead of fossil fuels.
ANSWERS
(a)
(i) I. Condensation II. Melting (ii) Iodine, Benzoic acid, Camphos, Dry Ice. Solid CO2 Naphthalene (iii) H2O(g) →H2O(g) (b) (i) Van des waals and hydrogen bonding II Van des waals forces (ii)I. The separation distance is smaller during fusion than during vaporization hence requires much lower energy than in vaporization and vice versa. II. Heating time NP is far much less than heating time in QR/ Heating time (c) (i) Hydrogen burns to produce steam which is a non pollutant/ does not cause pollution to the environment Hydrogen has a high energy content hence very small amount produce a lot of heat energy Hydrogen is renewable hence cannot be exhausted/ used completed. (ii) It can easily explore when burning/ highly flammable unlike fossils fuels expensive.
a) the schematic diagram shows part of the Solvay process used for the manufacture of sodium carbonate.
i) Explain how the sodium chloride required for this process is obtained from sea water.
ii) Two main reactions take place in UNIT I . The first one is the formation of ammonium hydrogen carbonate. I. Write an equation for this reaction II. Write an equation for the second reaction iii) State how the following are carried out: I Process I II) Process II iv)In an experiment to determine the percentage purity of the sample of sodium carbonate produced in the Solvay process, 2.15 g of the sample reacted completely with 40.0cm3 of 0.5 M sulphuric acid. I calculate the number of moles of sodium carbonate that reacted. II Determine the percentage of sodium carbonate in the sample. (Na= 23.0, C= 12.0, O = 16.0) b) Name two industrial uses of sodium carbonate
The set-up below (figure 2) was used to electrolyse a bromide of metal D DBr2
i) Write equation for the reactions at the
I cathode II anode ii) The electrodes used in the experiment were made of carbon and metal D. which of the two electrodes was used as the anode? Give a reason. iii) Give a reason why this experiment is carried out in a fume cupboard. iv) When a current of 0.4A was passed for 90 minutes, 2.31 g of metal D were deposited. I Describe how the amount of metal D deposited was determines. II Calculate the relative atomic mass of metal D. (I Faraday = 96500 coulombs)
a) Draw the structures of the following compounds:
i) 2- methylbut -2 ene; ii) heptanoic acid b) Describe a physical test that can be used to distinguish between methanol and hexanol. c) Use the flow chart below to answer the questions that follow.
i) Name: (I) the type of reaction that occurs in step II; (II) Substance B. ii) Give the formula of substance C. iii) Give the reagent and the conditions necessary for the reaction in step (IV)
ANSWERS
(b)
a) Two reagents that can be used to prepare chlorine gas are manganese (IV) oxide and concentrated hydrochloric acid.
i) Write an equation for the reaction. ii) Give the formula of another reagent that can be reacted with concentrated hydrochloric acid to produce chlorine gas. iii) Describe how the chlorine gas could be dried in the laboratory b) In an experiment, dry chlorine gas was reacted with aluminium as shown in figure 1.
i) Name substance A.
ii) Write an equation for the reaction that took place in the combustion tube. iii) 0.84 g of aluminium reacted completely with chlorine gas. Calculate the volume of chlorine gas used (Molar gas volume is 24dm3, Al = 27). iv) Give two reasons why calcium oxide is used in the set up.
Starting with red roses, describe how;
(i) a solution containing the red pigment may be prepared (ii) the solution can be shown tobe an indicator.
ANSWERS
(i)Crush the roses with a suitable solvent Filter to obtain pigment
(ii)Add pigment to an acid . It turns read
Sulphur dioxide and nitrogen dioxide react as shown in the equation below
SO2(g) + NO2(g) → SO3(g) + NO(g)
(i) Using the oxidation numbers of either sulphur or nitrogen, show that this is a redox reaction
(ii) Identify the reducing agent
4.76g of liquid ammonia and 4.76g of liquid nitrogen were each allowed warming up and hanging into gas at warm temperature and pressure. Relative atomic masses: H=1.0 and N=14.0. Using the data given above, explain which gas occupied the greater volume.
State and explain the observation that would be made when a few drops of concentrated sulphuric acid are added to a small sample of hydrated copper (II) sulphate
Study the flow chart below and answer the questions that follow
(a) Name:
Aluminium metal is a good conductor and is used for overhead cables. State any other two properties that make aluminium suitable for this use.
Study the information given in the table below and answer the questions that follow. The letters do not represents the actual symbols of the elements
(a) Select the elements which belong to the same
(e) The aqueous sulphate of element W was electrolyzed using inert electrodes Name the products formed at the:
The flow chart below shows the industrial preparation of ammonia and the process used in the manufacture of some ammonium compounds. Study and answer the questions that follow
(a) Give the name of the
(c) Explain why it necessary to compress nitrogen and hydrogen in this process (d) Write an equation for the reaction which takes place in step 6 (e) Name the catalyst and the reagents used in step 3 Catalyst Reagent (f) Name compound Z1 (g) Give one commercial use of compound Z2
(a) An ore is suspected to contain mainly iron. Describe a method that can be used to confirm the presence of iron in the ore
(b) Excess carbon monoxide gas was passed over a heated sample of an oxide of iron as shown in the diagram below. Study the diagram and the data below it to answer the questions that follow.
Mass of empty dish = 10.98g
Mass of empty dish 4 oxide of iron = 13.30g Mass of empty dish 4 residue = 12.66g
(c) Corrosive is a destructive process in which iron which is converted into hydrated iron (III) oxide State:
(d) Explain why it is not advisable to wash vehicles using seawater
(a) The following equations represents two different types of reactions
(i) nC4H8(g) → (C4H8)n(s) (ii) C2H6(g) + CI2(g) → C2H5CI(I) + HCI(g) State the type of reaction represented by: (i) (ii) (b) The fermentation of glucose produces ethanol as shown in the equation below C2H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g)
(c) The molecular formula of a hydrocarbon is C6H14. The hydrocarbon can be converted into two other hydrocarbons as shown by the equation below (i) Name and draw the possible structural formula of X Name Structural formula (ii) State and explain the observation that would be made if a few drops of bromide water were added to a sample of X. (iii) Write an equation for the complete combustion of C3H8
The set – up below was used to prepare anhydrous chlorides of a number of elements in a laboratory where no fine cupboard was available. The chlorides were to be collected in flask
The following table shows the melting and boiling points of the chlorides that were prepared.
More Quiz
(a) The table below gives the solubilities of hydrated copper (II) sulphate in mol dm3 at different temperatures (i) On the grid provided, plot a graph of solubility of copper (II) sulphate (vertical axis) against temperature. (ii) From the graph, determine the mass of copper (II) sulphate deposited when solution is cooled from 700C to 400C. (Molar mass of hydrated copper (II) sulphate = 250g) (b) In an experiment to determine the solubility of sodium chloride, 5.0cm3 of a saturate solution of sodium chloride weighing 5.35g were placed volumetric and diluted to a total volume of 250cm3. 25.0cm3 of the dilute solution chloride completely reacted with 24cm3 of 0.1M silver nitrate solution. AgNO3(aq) + NaCI(aq) → AgCl(s) + NaNO3(aq) Calculate: (i) Moles of silver nitrate in 24cm3 of solution (ii) Moles of sodium chloride in 25.0cm3 of sodium (iii) Moles of sodium chloride in 250cm3 of solution (iv) Mass of sodium chloride in 5.0cm3 of saturated sodium chloride Solution (Na = 23.0, CI = 35.5) (v) Mass of water in 5.0cm3 of saturated solution of sodium chloride (vi) The solubility of sodium chloride in g/100 water |
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