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KCSE CLUSTER TESTS 24

Chemistry Paper 2

1.

The table below shows the Atomic numbers of some elements represented by letter J to Q (Letters
do not represent their actual symbols). Study the table and answer the questions that follows.

d) Element N combines with oxygen to form an oxide using dots (.) and crosses (x) to represent
the outermost energy level electrons, show how the two elements combine.
(2mks)
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e) Select the most reactive metal and non metal and give reasons for your answer.
Metal……………………………………………………………………………………………
……………………( ½mk)

Reason ………………………………………………………………………………………………………………( ½ mk)
Non- metal…………………………………………………………………………………………………………( ½mk)
Reason………………………………………………………………………………………………………………..( ½ mk)
f) State one physical and one chemical property that J and Q have in common. (2mks)
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g) What name is given to the groups of elements to which P belong? (1mk)
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h) i) Element K consists of two isotopes with relative abundance of 75% and 25% and mass number of 35 and 37 respectively. Find the relative atomic mass of K. (2mks)
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ii) Explain why the relative atomic mass of K is not a whole number. (1mk)
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14 marks

2.

The diagram below represents the Haber process for the manufacture of ammonia. Study it and answer the questions that follow.

11 marks

3.

A student was provided with 2M sodium hydroxide solution and 4M hydrobromic acid solution. She was asked to investigate the equation of reaction between the two substances and hence determine the molar enthalpy of neutralization. The following results were obtained.

a) i) Plot a graph of temperature of the mixture against the volume of the acid added on the graph provided. (3mks)

ii) Use your graph to determine the room temperature at the start of the experiment. (1mk)

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iii) What is the significance of the highest temperature of the solution mixture.
(1mk)
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iv) Why did the temperature rise after the first addition of the acid but fell in the later additions. (2mks)
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v) Use your graph to find the volume of 4M hydrochloric acid that just neutralized 20.0cm3 of 2M sodium hydroxide. (1mk)
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b) Calculate the number of moles of:
i) Hydrobromic acid in a(V) above. (1mk)
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ii) Sodium hydroxide in 20.0cm3 of 2M NaOH solution. (1mk)
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c) Use your answers in b above to write an equation of the reaction taking place in the experiment. (2mks)
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d) Determine the temperature rise â–ºT, from the graph and calculate the molar enthalpy of neutralization of hydrobromic acid (specific heat capacity of water =4.2J/g/k; density=1g/cm3) (2mks)
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e) The molar heat of neutralization is 57.3KJ/mol give a reason why the students was lower. (2mks)
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14 marks

4.

Study the chart below answer the questions that follow.

a) i) Identify the process that could be
I. Dehydration (1mk)
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II. Polymerization (1mk)
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III. Hydrogenation (1mk)
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IV. Cracking (1mk)
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ii) State one observation in process 7 (1mk)
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iii) Write an equation showing how compound
I . J reacted with soda lime. (1mk)
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II. K was formed. (1mk)
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iv) Draw the structural formula of second member of the homologous series of alkyne
L. (1mk)
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b) An organic compound has empirical formula CH2O. The compound produces carbon (IV) oxide gas when reacted with NaHCO3. The compound has molar mass of 60. Find its molecular formular (H=1, C=12, O=16). (2mks)
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c) Name the following compounds

14 marks

5.

The set up below was used in preparation and collection of carbon (II) oxide and thereafter investigate properties of carbon (II) oxide.

a) Explain why calcium carbonate cannot be replaced by lead carbonate. (1mk)
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b) Write an equation for the reaction taking place in tube I. (1mk)
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c) What is the role of a chemical in flask 2 (1mk)
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d) State one observation during the reaction in tube 2 (1mk)
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e) State the precaution to be taken in this experiment (1mk)
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f) State two properties of carbon (ii) oxide from the set-up. (1mk)
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g) Using dots (.) and crosses (x) to represent electrons, show bonding in carbon (II) oxide. (2mks)
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h) When moist carbon (iv) oxide is passed through fused calcium oxide, the mass increases, use equations to explain why (2mks)
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14 marks

6.

In an experiment to determine the percentage composition of brass, an alloy of zinc and copper, a student was provided with 4g of powdered brass. The student then took 200cm3 of 6M hydrochloric acid and warmed it in flask. She then transferred all the 4g of powdered brass into the warm acid and collected all the gas produced. The volume of the gas was 1275cm3. (R.A.M of Zn=65, Cu=63.5)
a) Why was the acid warmed. (1mk)
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b) Name
i) the gas produced (1mk)
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ii) the reagent in the brass that reacted. (1mk)
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c) Calculate the moles of the gas produced.(molar gas volume is 24000cm3) (1mk)
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d) Calculate the mass of zinc and copper in brass. (3mks)
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e) The reaction mixture above was treated with sodium hydroxide and ammonium solution and a white precipitate soluble in excess alkali was observed. Name the precipitate formed here. (1mk)
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9 marks

7.

a) Name the solution and catalyst used in the preparation of oxygen in the laboratory.
(1mk)
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b) Give the chemical equation for the reaction above. (1mk)
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c) In an experiment to determine the proportion of oxygen in air, copper turnings were packed excess in a long combustion tube connected to two syringes of 120cm3 each in volume. Syringe R contained 120cm3 of air while syringe S was closed and empty as shown below.

Air was passed over heated copper turnings slowly and repeatedly until there was no further change in volume 95.5cm3 of air remained in syringe R.
i) why was copper packed in excess? (1mk)
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ii) Why was air passed over heated copper slowly. (1mk)
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iii) State one observation made in the combustion tube during the experiment. (1mk)
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iv) Give an equation for the reaction that took place in the combustion tube. (1mk)
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v) Determine the percentage of oxygen used up during the experiment. (1mk)

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vi) Give a hospital use of oxygen. (1mk)
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8 marks