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The figure below shows how the rate of the following reaction varies with the time.
i) Which of the two curves represent the rate of the reverse reaction? Give a reason
ii) What is the significance of point X and Y on the figure? b) State and explain the effect of an increase in pressure on the rates of the following reactions. 
i) On a grid plot a graph of volume of gas produced (vertical axis) against time
ii) From the graph, determine the rate of the reaction at: (I) 15 seconds (II) 120 seconds (III) Give a reason for the difference between the two values.
ANSWERS
(a)Curve 1
The concentration of products are increasing The rate of reaction is increasing. At time x equilibrium has been established, the rate of forward reaction is equal to the rate of reverse reaction and this has a value of Y. (b)(i) Increasing pressure increases rate of reaction. Molecules are brought closer, more collision of gases particles. Increasing pressure has no effect on liquids. 
The melting and boiling points of zinc are 419°C and 907°C respectively. One of the ores of zinc blende. To extract zinc, the ore is first roasted in air before feeding it into a furnace.
a. i) Write the formula of the main zinc compound in zinc blende. ii) Explain using an equation why it is necessary to roast the ore in air before introducing it into the furnace b. The diagram below shows a simplified furnace used in the extraction of zinc. Study it and answer the questions that follows: 
i) Name two other substance that are also introduced into the furnace together with roasted ore.
ii) The main reducing agent in the furnace is carbon(II) oxide. Write two equations showing how it is formed. iii) In which physical state is zinc at point Y in the furnace? Give a reason iv) Suggest a value for the temperature at point X in the furnace. Give a reason. v) State and explain one environmental effect that may arise from the extraction of zinc from zinc blende vi) Give two industrial uses of zinc.
ANSWERS
a) A student set up the apparatus as shown in the diagram below to prepare and collect dry ammonia gas.
i) Identify two mistakes in the set up and give a reason for each mistake.
I. Mistake Reason II. Mistake Reason ii) Name a suitable drying agent for ammonia iii) Write an equation for the reaction that occurred when a mixture of ammonium chloride and calcium hydrogen was heated. iv) Describe one chemical test for ammonia gas d) Ammonia gas is used to manufacture nitric (V) acid, as shown below. 
i) This process require the use of a catalyst. In which unit is the catalyst used
ii) Identify compound A and B A B iii) Using oxidation number, explain why the conversion of ammonia to nitric(V) acid is called catalytic oxidation of ammonia iv) Ammonia and nitric(V) acid are used in the manufacture of ammonium nitrate fertilizer. Calculate the amount of nitric (V) acid required to manufacture 1000kg ammonium nitrate using excess ammonia.(N=14.0, H=1.0, O=16.0)
ANSWERS
a. 50cm3 of 1M copper (II)sulphate solution was placed in a 100cm3 plastic beaker. The temperature of the solution was measured. Excess metal A powder was added to the solution, the mixture stirred and the maximum temperature was repeated using powder of metals B and C. The results obtained are given in the table below:
i. Arrange the metal A, B, C and copper in order of reactivity starting with the least reactive. Give reasons for the order.
ii. Other than temperature change, state one other observation that was made when the most reactive metal was added to the copper(II) sulphate solution.
b. The standard enthalpy change of formation of methanol is -239 kJmol-1
i) Write the thermol chemical equation for the standard enthalpy change of formation of methanol. 
iii) The calculate enthalpy change in part B(ii) (II) above differ from the standard enthalpy change of formation of methanol. Give a reason.
ANSWERS
Use the information in the table below to answer the questions that follow. The letters do not represent that actual symbols of the elements.
a) Give the reasons why the meling point of:
i) S is higher than that of R ii) V is lower than that of U b) How does the reactivity of W with chlorine compare with that of R with chlorine? Explain, c) Write an equation for the reaction between T and excess oxygen
d) When 1.15g of R were reacted with water, 600cm3 of gass was produced.
Determine the relative atomic mass of R. (Molar gas volume = 24000cm3) e) Give one use of element V
ANSWERS
(a)(i) Metallic bonds in S are stronger than in R.
(ii) V is monoatomic (independent) hence weaker van der waals forces while U is diatomic hence stronger van der waals forces V has less van der waals forces while U has more van der waal forces (b) reacts more vigorously/more reactive/reacts faster - reactivity of group 1 elements increases down the group/Ionisation energy is less than that of R - easier to lose outer electron in W than in R W is more electropositive than R 
(a).i) Give the name of the following compounds:
b). Describe a chemical test that can be carried out in order to distinguish between
c). Study the flow chart below and answer the questions that follows
i) Name the compounds:
(I). L (II). N ii) Draw the structural formula of compound M showing two repeat units iii) Give the reagent and the conditions used in step I iv) State the type of reaction that take place in: (I). Step 2 (II). Step 3
d). The molecular formula of compound P is C2H2Cl4. Draw the two structural formulae of compound P
ANSWERS
a) Which one of the following compounds; urea, ammonia, sugar and copper (II) chloride will conduct an electric current when dissolved in water? Give reasons.
b) The diagram below shows an electrochemical cell. Study it and answer the questions that follows. 
i) Show on the diagram using an arrow, the direction of flow of electrons
ii) Name two subsrances that are used to fill the part labeled L c) In an experiment to electroplate iron with silver, a current of 0.5 amperes was passed through a solution of silver nitrate for an hour i) Give two reasons why it is necessary to electroplate iron with silver ii) Calculate the mass of silver that was deposited on iron (Ag = 108, 1 Faraday = 96,500 coulombs)
ANSWERS
The atomic numbers of phosphorus, sulphur and potassium are 15, 16 and 19 respectively. The formulae of their ions are P3-,S2- and K+. These ions have the same number of electrons.
a) Write the electron arrangement for the ions. b) Arrange the ions in the order of increasing ionic radius starting with the smallest. Give a reason for the order.
ANSWERS
A water trough, aqueous sodium hydroxide, burning candle, watch class and a graduated gas jar were used in an experimental set up to determine the percentage
of active part of air. Draw a labeled diagram of the set up at the end of the experiment.
ANSWERS
A sample of river water was divided into three portions. The table below shows the test carried out on the portions and the observations made.
Complete the table by filling in the inferences.
ANSWERS
Describe how a solid sample of the double salt, ammonium iron(II) sulphate, can be prepared using the following reagents; Aqueous ammonia, sulphuric(VI) acid and iron metal.
ANSWERS
The curves below shows how the electronic conductivity of hydrochloric and ethanoic acids vary with concentration.
Explain why the electrical conductivity of 0.01M hydrochloric acids is higher than that of 0.01M ethanoic acid.
ANSWERS
Nitrogen and hydrogen react to form ammonia gas as shown in the following equation:
a) The figure below shows how the percentage of ammonia gas in the equilibrium mixture change with temperature.
Explain why the percentage of ammonia gas change as shown in the figure.
b) On the axes below, sketch a graph showing how the percentage of ammonia gas in equilibrium mixture changes with pressure. 
ANSWERS
The use of CFCs has been linked to depletion of the ozone layer.
a) What does CFC stand for? b) Explain the problem associated with the depletion of the ozone layer c) State another environment problem caused by CFCs
ANSWERS
(a)Chlorofluorocarbon
(b)When ozone is depleted, high energy UV radiations reach the earth, which may cause skin cancer to human beings. (c)Global warmings, /green house effect.
In an experiment to prepare nitrogen (I) oxide, ammonium nitrate was gently heated in a flask.
a) Write the equation for the reaction that took place in the flask. b) State and explain how the gas was collected. c) A sample of the gas was tested with damp blue and red litmus papers. What observations were made?
ANSWERS
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December 2024
AuthorMaurice Atika is a teacher and a netprenuer. |
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