KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
Hydrogen and oxygen can be obtained by electrolysis of acidified water.
Using equations for the reactions at the electrodes, explain why the volume of hydrogen obtained is twice that of oxygen. ​Related Chemistry Questions and Answers on Electrochemistry Form 4 Level
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a) what is meant by molar heat of solution?
b) the lattice energy of sodium bromide and hydration energies of sodium and bromide ions are: 733,406 and 335 kJmol -1 respectively. i) Complete the energy cycle diagram below by inserting the values of ΔH1, ΔH2, and ΔH3
ii) Determine the molar heat of solution of solid sodium bromide.
Using dots (.) and crosses (x) , show bonding in:
a) The compound formed when nitrogen reacts with fluorine (Atomic numbers F=9, N=7); b) Sodium oxide.(Atomic numbers Na= 11, 0 = 8)
When aluminium oxide was electrolysed, 1800kg of aluminium metal were obtained.
a) Write equation for the formation of aluminium metal b) Calculate the quantity of electricity in faradays used (Al=27)
An isotope of element E has 34 neutrons and its mass number is 64. E forms a cation with 28 electrons. Write the formula of the cation with 28 electrons. Write the formula of the cation indicating the mass and atomic numbers.
In terms of structure and bonding, explain why the melting point of oxygen is much lower than that of sodium.
ANSWER
ANSWERS
(a) Water
(b) The second / other product of burning candle is carbon (IV) oxide (l). It can be prevented from getting into the environment by passing it though a hydroxide solution/ alkaline solution e.g. K.O.H NaOH or aqueous ammonia . To form K2CO3
ANSWERS
(i) 2.8.8 (ii) 2.8.2
Hardness of water may be removed by either boiling or addition of chemicals
a) write an equation to show how boiling removes hardness of water. b) name two chemicals that are used to remove hardness of water.
A sealed glass tube containing air at s.t.p was immersed in water at 1000c. Assuming that there was no increase in the volume of the glass tube due to the expansion of the glass, calculate the pressure of the inside tube.
(standard pressure = 760mmHg,)
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The scheme below shows some reaction sequence starting with solid N.
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The formula given below represents a portion of a polymer Give:
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The diagram below represents a charcoal burner. Study it and answer the questions that follow
Write equations for the reactions taking place at I and I and II
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Describe how a solid sample of lead (II) Chloride can be prepared using the following reagents, dilute nitric acid, dilute hydrochloric acid and lead carbonate.
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ANSWERS
(a) Energy required to remove 1 mole of electrons from 1 mole of gaseous atoms
(b) B 418??? It loses electrons most readily Reject lowest i.e. Mg (HCO3) 2 aq →MgCS O3 + H2O + CO2 (g)
(a) Define the standard enthalpy of formation of a substance
(b) Use the thermochemical equations below to answer the questions that follow.
(i) Name two types of heat changes represented by ΔH3
(ii) Draw an energy level diagram for the reaction represented by equation 1 (iii) Calculate the standard enthalpy of formation of ethane (iv) When a sample of ethane was burnt, the heat produced raised the temperature of 500g of water by 21. 5 K, (specific heat capacity of water = 4.2Jg-1K). Calculate the: I. Heat change for the reaction II. Mass of ethane was burnt. ( relative formula mass of ethane= 30)
The diagram below represents a set up that can be used to electrolyze aqueous copper (II) sulphate.
(a) (i) Describe how oxygen gas is produced during the electrolysis
(ii) Explain why copper electrodes are not suitable for this electrolysis (b) Impure copper is purified by an electrolytic process (i) Name one ore from which copper is obtained (ii) Write the equation for the reaction that occur at the cathode during the purification of copper (iii) In an experiment to electroplate a copper spoon with silver, a current of 0.5 A was passed for 18 minutes. Calculate the amount of silver deposited on the spoon (π = 96500 coulombs, Ag = 108) (iv) Give two reasons why some metals are electroplated
(a) Alkanes, alkenes and alkynes can be obtained from crude oil. Draw the structure of the second member of the alkyne homologous series.
(b) Study the flow chart below and answer the questions that follow
(i) State the conditions for the reaction in step 1 to occur
(ii) Identify substance II (iii) Give: I. One advantage of the continued use of substance such as J II The name of the process that takes place in step III III The name and the formula of substance K Name: Formula: (iv) The relative molecular mass of J is 16,800. Calculate the number of monomers that make up J. (c) The table below give the formula of four compounds L,M,N and P
Giving a reason in each case, select the letter which represents a compound that:
(i) Decolorizes bromine in the absence of UV light (ii) Gives effervescence when reacted with aqueous sodium carbonate Urea, (NH2)2CO is prepared by the reaction between ammonia and carbon dioxide. 2NH3(g) + CO2(g) → (NH2)2CO(aq) + H2O(l). In one process, 680 kg of ammonia were reacted with excess carbon dioxide. Calculate the mass of urea that was formed. (H = 1.0, c+ 12.0, N =14.0, O = 16.0 and relative molecular mass of ammonia = 17) Calculate the mass of Urea that was formed
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The grid below shows part of a periodic table. The letters do not represent the actual symbols of the elements
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Draw the structural formula of:
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a) (i) State the Le chatelier‟s principle.
(ii) Carbon (II) oxide gas reacts with steam according to the equation; CO(g) + H2O(g)→ H2(g)+ CO2(g) What would be the effect of increasing the pressure of the system at equilibrium? Explain. b) The table below gives the volumes of oxygen gas produced at different times when hydrogen peroxide decomposed in the presence of a catalyst.
(i) Name the catalyst used for this reaction
(ii) On the grid provided, draw the graph of volume of oxygen gas produced (vertical axis) against time. (iii) Using the graph, determine the rate of decomposition of hydrogen peroxide after 24 seconds. (iv) Give a reason why the total volume of oxygen gas produced after 50 seconds remains constant.
ANSWERS
(a)(i) When change is made to a system in equilibrium the System moves so as to oppose the change.
(ii)Pressure has no effect to equilibrium The moles/Volume/ molecules of gases is reactants and product are equal (iii) DH –ve ( negative) Since lowering of temperature moves to equilibrium to direction which heat is produced. Decrease in temperature favours exothermic reaction (b) (i) Manganese IV oxide
(a) Describe the process by which Nitrogen is obtained from air on a large scale.
(b) Study the flow chart below and answer the questions that follow.
(i) Identify gas J.
(ii) Using oxidation numbers, show that ammonia is the reducing agent in step (VI) (iii) Write the equation for the reaction that occurs in step (V). (iv) Give one use of ammonium nitrate. c) The table below shows the observations made when aqueous ammonia was added to cations of elements F2F and G until in excess.
(i) Select the cation that is likely to be Zn2+
(ii) Given that the formula of the cation of element E is E 2+, write the ionic equation for the reaction between E2+ (aq) and aqueous ammonia. |
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