KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
In order to determine the molar of neutralization of sodium hydroxide, 100cm3 of 1M sodium hydroxide and 100cm3 of 1 M hydrochloric acid both at the same initial temperature were mixed and stirred continuously with a thermometer. The thermometer of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained. Thereafter the temperature of the solution was recorded for a further two minutes
(a)
I. What is the significance of point Y2? II. Explain why there is a temperature change between points; Y1 and Y2 Y3 and Y4 (iv) In the initial temperature for both solutions was 24.50C and the highest temperature attained by the mixture was 30.90C Calculate the: I. heat change for the reaction (specific heat capacity of the solution = 4.2Jg -1K-1 and the density of the solution = 1.0g/cm3 II. Molar heat of neutralization of sodium hydroxide (v) Explain how the value of the molar heat of neutralization obtained in this experiment would compare with the one that would be obtained if the experiment was repeated using 100cm3 of 1 Methanoic acid instead of hydrochloric acid. (b) On the grid provided below, draw an energy level diagram for the reaction between hydrochloric acid and sodium hydroxide
0 Comments
ANSWER
(a) Energy of the activated energy Therefore more molecules will take part in effective collision. Or Energy of the activated/intermediate complex of the unanalyzed reaction
(b) Catalyst lowers the activation energy therefore more molecules will take effective collision
ANSWERS
ANSWERS
(a) Temperature and pressure are directly proportional (l) IR words towards that of real
(b) With increase in temperature, the gas particles gain more Kinetic energy They move faster and collide with the walls of the container more frequently hence increasing pressure.
For each of the following reactions, state the observation and write the formula of the
Compound responsible for the observation: a) Bromine water is added to aqueous potassium iodide; b) Excess aqueous ammonia is added to copper (II) hydroxide (precipitate).
ANSWERS
(a) SiH4 it has a higher boiling point
(b) No hydrogen bonding in CH4 and SiH4 while the hydrogen bond in H2O is stronger than that in H2S
ANSWERS
(a) Pale green solution turns yellow
(b) Sodium hydroxide Potassium hydroxide (c) Water
ANSWERS
Give the name of the product formed when magnesium reacts with phosphorus.
ANSWERS
ANSWERS
(a) Chemical change
(b) Physical change (c) Chemical change
The figure below represents the set up that was used to crack an alkane.
a) What was the purpose of the sand?
b) After some time, a colourless gas G collected in the test-tube. Describe a chemical test and the observations that would be made in ordered to identify the class of compounds to which gas G belongs.
ANSWERS
(a) Catalyst or words to that effect
(b) Add bromine water or acidified potassium magnate (VII) if they decolorize then gas is either an alkene or an alkynes
ANSWERS
What is the oxidation number of chlorine in CO4
Expected Response
The column below was used do soften hard water
Expected Response
A hydrocarbon slowly decolorizes bromine gas in the presence of sunlight but does not decolourise acidified potassium permanganate
Name and draw the structural formula of the fourth member of the series to which the hydrocarbon belongs.
Expected Response
The table below gives the energy required to remove the outermost electron for some group I elements
Arrange the elements in order of their reactivity starting with the most reactive
Expected Response
The diagram below shows the physical state of matter. Study it and answer the questions that follow
Identify the processes R, V, w and U
(c) Name one substance which can undergo the process represented by S and T.
Expected Response
A beekeeper found that when stung by a bee, application of a little solution of hydrogen carbonate helped to relieve the irritation from the affected area. Explain.
Expected Response
A student used the set up shown in the diagram below in order to study the reactions of some metals with steam. The experiment was carried out for ten minutes
a) What observation would be made if gas F is ignited?
b) When the experiment was repeated using iron powder instead of magnesium ribbon very little gas F was obtained. i) Give a reason for this observation ii) What change in the conditions of the experiment should the student have made in order to increase the volume of gas F Produced?
ANSWERS
(a) The gas burns with a blue flame
(b) (i) The iron isles reactive than magnesium (ii) Heat the iron powder
a) Draw and name the structure of the compound formed when one mole of ethyne reacts with one mole of hydrogen bromide.
b) Draw the structures of the alkynes whose molecular formula is C4H6
When 8.53 of sodium nitrate were heated in an open test-tube the mass of oxygen gas produced was 0.83 g .
Given the equation of the reaction as 2NaNO3(s) →2NaNO2(s) + O2(g) Calculate the percentage of sodium nitrate that was converted to sodium nitrite (Na = 23.0 N = 14.0 O = 16.0)
The standard reduction potentials of two half –cells are:
Ag+(aq) + e → AG(s) ; E = 0.80V 2H2O (l) + 2e → H2 (g) + 2OH (aq); E1 = 0.83V Draw a labelled diagram of an electro chemical cell that can be constructed using the two half –cells
Starting with 50 cm3 of 2.8M sodium hydroxide, describe how a sample of pure sodium sulphate crystals can be prepared.
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