KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
The set up shown below was used to investigate a property of hydrogen gas.
State and explain the observation that would be made in the glass tube if beaker A was filled with hydrogen gas.
ANSWERS
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Acidified potassium manganate (VII) solution is decolourised when sulplur (IV) oxide is bubbled through it. The equation for the reaction is given below.
2H2O(1) + 5S02(g) + 2KMnO4(aq) —►K2SO4(aq) + 2MnSO4(aq)+ 2H2SO4(aq) (a) Which reactant is oxidised? Explain. (b) Other than the manufacture of sulphuric (VI) acid, state one other use of sulphur (IV) oxide.
Study the scheme below and answer the questions that follow
a) Identify solid E.
b) Write an ionic equation for the reaction in step II that produces solid F.
(a) The following diagrams show the structures of two allotropes of carbon. Study them and answer the questions that follow
(i) Name allotrope
M N (ii) Give one use of N (iii) Which allotrope conducts electricity? Explain
(b) In an experiment, carbon dioxide gas as passed over heated charcoal and the gas produced collected as shown in the diagram below
(i) Write an equation for the reaction that took place in the combustion tube
(ii) Name another substance that can be used instead of sodium hydroxide (iii) Describe a sample chemical test that can be used to distinguish between carbon dioxide and carbon monoxide (iv) Give one use of carbon monoxide
(a)
(b) A sample of hydrogen chloride gas was dissolved in water to make 250cm3 of solution required 46 cm3 of 11.0M Sodium hydroxide for complete neutralization.
Study the flow chart below and answer the questions that follow.
(a) Name a suitable drying agent for ammonia.
(b) Describe one chemical test for ammonia. (c) Name X.
ANSWERS
(a) Calcium Oxide
(b) Expose ammonia to hydrogen chloride gas, dense white fumes of ammonium chloride are observed. (c)Steam/water .
State and explain the function of tartaric acid in baking powder
Expected Response
It reacts with NaHCO3 to form CO2 which causes the dough to rise.
In an experiment, ammonia chloride was heated in a test tube. A moist red litmus paper placed at the mouth of the test tube first changed blue then red. Explain these observations
Expected Response
NH4Cl decomposes to form NH3(g) and HCl(g).Ammonia diffuses faster than HCl because its light. Ammonia is basic and thus red litmus paper turns blue while HCl is acid thus blue litmus turns red.
Explain why it is not advisable to leave a Jiko with burning charcoal in a closed room where one is sleeping.
Expected Response
The supply of oxygen in the room will be limited leading to formation of CO which is poisonous.
When a solid sample of sulphur is heated in a test tube, it changes into a liquid, which flows easily. On further heating, the liquid darkness and does not flow easily. Explain these observations.
Expected Response
Solid sulphur is made of S8 rings. It melts into aliquid of S8 rings, On further heating the rings open up to form long chains of sulphur atoms, which then entangle making it viscous and dark, or sulphur melts into S8 molecules. The molecules join up to form long chain which entangle making it viscous and dark
Study the information in the table below and answer the questions that follow. The letters do not represent the actual symbols of the elements)
Select an element which
Expected Response
A given volume of ozone, (O3) diffused from a certain apparatus in 96 seconds. Calculate the time taken by an equal volume of carbon dioxide (CO2) to diffuse under the same conditions (O = 16.0, C = 12.0) 20.0cm3 of a solution containing 4 gm per litre of sodium hydroxide was neutralized by 8.0cm3 of dilute sulphuric acid. Calculate the concentration of sulphuric acid in moles per litre (Na = 23.0, O = 16.0, H = 1.0)
A student set up the apparatus shown below to prepare ammonia gas and react it with copper (II) sulphate solution
(a) Identify solution V
(b) State the observations which were made in the beaker
Expected Response
A hydrocarbon P was found to decolourise bromine water. On complete combustion of 2 moles of P, 6 moles of carbon dioxide and 6 moles of water were formed
The equation below represents a redox reaction
a) Write down the equation for the reduction process
b) Which substance is oxidized
The simplified flow chart shows some of the steps in the manufacture of sodium carbonate by the Solvay process
(a) Identify substance L
(b) Name the process – taking place in step II (c) Write an equation for the reaction, which takes place in step III
The empirical formula of A is CH2Br. Given that 0.470g of A occupies a volume of 56cm3 at 546K and 1 atmospheric pressure, determine its molecular formula.(H = 1.0, C = 12.0, Br = 80.0, molar gas volume at STP = 22.4 dm3).
a) The diagram below shows a set –up used by as a student in an attempt to prepare and collect oxygen gas
c) The reaction between sulphur dioxide and oxygen to form trioxide in the contact process in exothermic. Factory manufacturing sulphuric acid by contact process produces 350kg of sulphur trioxide per day (conditions) for the reaction catalyst. 2 atmospheres pressure and temperatures between. (400 – 5000C) i) What is meant by an exothermic reaction? ii) How would the yield per day of sulphur trioxide be affected Temperatures lower than 40000C are used? Explain.
10cm3 of concentrated sulphuric (VI) acid was diluted to 100cm3. 10cm3 of the Resulting solution was neutralised by 36cm3 of 0.1M sodium hydroxide solution. Determine the mass of sulphuric (VI) acid that was in the concentrated acid (S = 32.0; H = 1.0; O = 16.0).
(a) When excess calcium metal was added to 50 cm3 of 2 M aqueous copper (II) nitrate in a beaker, a brown solid and bubbles of gas were observed.
(i) "Write two equations for the reactions which occurred in the beaker. (ii) Explain why it is not advisable to use sodium metal for this reaction.
(b) Calculate the mass of calcium metal which reacted with copper (II) nitrate solution. (Relative atomic mass of Ca = 40)
(c) The resulting mixture in (a) above was filtered and sodium hydroxide added to the filtrate dropwise until in excess. What observations were made? (d) (i) Starting with calcium oxide, describe how a solid sample of calcium carbonate can be prepared. (ii) Name one use of calcium carbonate
ANSWERS
(c)A white precipitate is formed which is insoluble in excess.
(d) (I) Add dilute nitric (V) acid to calcium oxide to form the soluble salt calcium nitrate. Add sodium carbonate (another soluble salt) to form insoluble. Calcium Carbonate and sodium nitrate . Filter out the calcium carbonate, wash it with distilled water to remove traces of sodium nitrate and dry between filter papers (ii) Manufacture of cement Manufacture of sodium carbonate.
The flow chart below shows some of the processes involved in large scale production of sulphuric (VI) acid. Use it to answer the questions that follow.
a) Describe how oxygen is obtained from air on a large scale
(b) (i) Name substance A. (ii)Write an equation for the process that takes place in the absorption chamber. (c) Vanadium (V) oxide is a commonly used catalyst in the contact process. (i) Name another catalyst which can be used for this process. (ii) Give two reasons why vanadium (V) oxide is the commonly used catalyst. (d) State and explain the observations made when concentrated sulphuric (VI) acid is added to crystals of copper (II) sulphate in a bearer. (e) The reaction of concentrated sulphuric (VI) acid with sodium chloride produces hydrogen chloride gas. State the property of concentrated sulphuric (VI) acid , illustrated in this reaction. (f) Name four uses of sulphuric (VI) acid
The data given below was recorded when Metal M was completely burnt in air. M is not the actual symbol of the metal. (RA.M; M = 56, O ==16)
Mass of empty crucible and lid = I0.240g Mass of crucible, ;lid and metal M = 10.352g Mass crucible, lid and metal oxide = 10.400g (a) Determine the mass of: (i) Metal M (ii) oxygen. (b) Determine the empirical formula of the metal oxide.
(a) State the Gay Lussac's Law.
(b) 10cm3 of a gaseous hydrocarbon, C2HX required 30cm3 of oxygen for complete combustion. If steam and 20cm3 of carbon (IV) oxide were produced, what is the value of X?
When excess carbon monoxide gas was passed over heated lead (II) oxide in combustion tube, lead (II) oxide was reduced
(a) Write an equation for the reaction, which took place (b) What observation was made in the combustion tube when the reaction was complete? (c) Name another gas, which could be used to reduce lead (II) oxide
Expected Response
(a) Pb(s) + CO(g) →Pb(s) + CO2(g)
(b) Silvery white or grey metal/ shiny grey metal (c) Hydrogen gas / ammonia |
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