KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
A few crystals of potassium permanganate were carefully placed into water in a beaker at one spot. The beaker was left undisturbed for two hours. State and explain the observation that was made.
answer
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Nitrogen (II) oxide and nitrogen (IV) oxide are some of the gases released from car exhaust pipes. State how these gases affect the environment
answer
When excess dilute hydrochloric acid was added to sodium , 960cm3 of sulphur (IV) oxide gas was produced. Calculate the mass of sodium sulphite that was used. (molar mass of sodium = 126 g and molar gas volume= 24000cm3
(a) Sulphur exists in two crystalline forms
(b) Name one crystalline form of sulphur
But -2- ene undergoes hydrogenation according to the equation given below
CH3CH = CHCH3 (g) + H2 (g) →CH3CH2CH2CH3 (g) (a) Name the product formed when but -2 – ene reacts with hydrogen gas (b) State one industrial use of hydrogenation
answers
a)Butane
b)Hardening of oils in the manufacture of margarine
(a) Give a reason why concentrated sulphuric acid is not used to dry ammonia gas
(b) Name one suitable drying agent for ammonia gas
answers
a)Being acidic, it would react with the basic ammonia
b)CaO
In an experiment 30cm3 of 0.1 M sulphuric acid were reacted with 30cm3 of 0.1 M sodium hydroxide
(a) Write in equation of the reaction that took place (b) State the observations that were made when both and red litmus papers were dropped into the mixture (c) Give a reason for your answer in (a) above
expected response
Sulphur dioxide, it reacts with lime-water being an acid gas
The reaction of propane with chlorine gas gave a compound of formula C3H7Cl. a) What condition is necessary for the above reaction to take place? (1mk) b) Draw two structural formulae of the compound C3H7Cl (2mks)
expected response
Air is less dense than carbon dioxide and so it enters the porous pot faster than carbon dioxide out of it. This sets up a higher pressure; in the pot and the level rises as shown:
Zinc metal and hydrochloric acid reacts according to the following equation Zn(s) + 2HCI (aq)→ ZnCI2 (aq) + H2 (g) 1.96 g of zinc were reacted with 100cm3of 0.2M hydrochloric acid (a) Determine the reagent that was in excess (b) Calculate the total volume of hydrogen gas was liberated S.T.P (Zn= 65.4 Molar gas volume = 22.4 litres at S.T.P) A fixed mass of a gas has a volume of 250cm3 at a temperature of 270C and 750mm Hg pressure. Calculate the volume the gas would occupy at 420C (2mks)
The structures below represents a portion of a polymer
(a) Give the name of the polymer (b) Give one industrial use of the polymer
answer
Concentrated nitric (V) acid was added to iron (II) sulphate acidified with sulphuric acid and the mixture heated. The solution turned from pale green to yellow with evolution of brown gas. Explain these observations.
answer
In an experiment, sulphur dioxide gas was bubbled into water followed by chlorine gas. The resulting clear solution gave a white precipitate when mixed with a acidified barium chloride solution. Explain these observations
answers
The following two tests were carried out on chlorine water contained in two test tubes
(a) A piece of blue flower was dropped into the first – tube. Explain why the flower was bleached (b) The second test- tube was corked and exposed to sunlight after a few days, it was found to contain a gas that rekindled a glowing splint. Write an equation for the reaction which produced the gas (a) The diagram below shows a set-up that can be used to obtain nitrogen gas in an experiment. (i) Name liquid L (1mk) (ii) What observation would be made in tube K after heating for some time? (1mk) (iii) Write an equation for the reaction that took place in tube K. (1 mk) (iv) If 320 cm3 of ammonia gas reacted completely with the copper? Calculate: I Volume of nitrogen gas produced. (1mk) II the mass of copper oxide that reacted (3mks) (Cu = 63.5, O=16.O, one mole of gas occupies 24 liters at room temperature and pressure) (v) At the end of experiment the PH of the water in the beaker was found to be about ______________________ Explain (2mks) (b) In another experiment a gas jar containing ammonia was inverted over a burning splint. What observation would be made? (1mk) (c) Why is it advisable to obtain nitrogen from air instead ammonia? (1mk) a) In an experiment hydrogen chloride gas was prepared and reacted with aluminium turnings to form a solid q and gas R as shown in the diagram (i) Name: Liquid P : Solid Q (1mk) : Gas R (1mk) (ii) Name another substance that could serve the same purpose as the concentrated sulphuric acid. (1mk) (iii) Explain the following observation. When blue litmus paper was dipped into the water in the beaker at the end of the experiment it turned red. Explain why solid Q collects farther away from the heated aluminium (2mks) (b) (i) Write an equation for the reaction that takes place between ammonia gas and hydrogen gas (1mk) (ii) Calculate the mass of the product that would be formed when 2000cm3 of hydrogen chloride gas reacts completely with excess ammonia gas (H=1, O; N= 14.0, C1 = 35.5, one mole of gas occupied 24 litres at room temperature and pressure.) (3mks) A compound C4H10O_ is oxidized by excess acidified potassium permanganate to form another compound C4H8O2. The same compound C4H10O reacts with potassium to produce hydrogen gas. a) Draw the structural formula and name the compound CaH10O (1mk) b) Write an equation for the reaction between potassium and compound C4H10O.
State what would be observed when dilute hydrochloric acid is added to the products formed when a mixture of iron fillings and sulphur? (1mk)
Expected Response
A gas with a smell of rotten eggs is formed H2S gas is formed / A greenish solution is formed? Effervescence / A gas is produced / Black solid dissolves. (1mk)
Expected Response
Hydrogen, because it is lighter/ less denser / diffuses faster (2mks)
Expected Response
a) I – Molten sulphur
II – Super heated water / water
b) To force the molten sulphur out
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