KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
(a) Name the method that can be used to obtain pure iron (III) chloride from a mixture of iron (III) chloride and sodium chloride.
(b) A student was provided with a mixture of sunflower flour, common salt and a red dye. The characteristics of the three substances in the mixture are given in the table below.
The student was provided with ethanol and any other materials needed.
Described how the student can separate the mixture into its three components c) The diagram below show part of a periodic table. The letters do no represent the actual symbols of elements. Use the diagram to answer the questions that follow.
i) Explain why the oxidizing power of W is more than that of X
ii) How do the melting points of R and T compare? Explain iii) Sketch an element that could be used i) In weather ballons ii) For making a cooking pot d i) Classify the substances water, iodine, diamond and candle wax into elements and compounds
ii) Give one use of diamond
ANSWERS
(a)Sublimation
(b)Add ethanol to the mixture . Filter and evaporate filtrate to obtain red dye . Add water to the residue . Filter to obtain sunflower flour . Evaporate filtrate to obtain salt . OR Add H,O to mixture , filter , residue is sunflower , evaporate the water ; add ethanol to the residue filter . The filtrate is red dye. (3 marks) (c)(i) W accepts electrons more readily than X. W has small atomic radius/ W has less energy levels than X/ W has less screening effect than X/ W has greater effective nuclear attraction than X. W is more electro negative than X. (ii) T has a lower melting point than R because it exists in simple molecular form with weak Van der Waals forces while R has strong metallic bonds.
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(a) Draw the structure of the folio wing compounds.
(i) Butanoic acid; (ii) Pent-2-ene. (b) Explain why propan-1-ol is soluble in water while prop-1-ene is not. (Relative molecular mass of propan-1-ol is 60 while that of prop-1-ene is 42). (c) What would be observed if a few drops of acidified potassium manganate (VII) Were added to oil obtained from nut seeds? Explain. (d) State one method that can be used to convert liquid oil from nut seeds into solid. (e) Describe how soap is manufactured from liquid oil from nut seeds (f) 0.44 g of an ester A reacts with 62.5 cm3 of 0.08 M potassium hydroxide giving an alcohol Band substance C. Given that one mole of the ester reacts with one mole of the alkali, calculate the relative molecular mass of the ester.
(a) (i) Carbon (IV) oxide is present in soft drinks. State two roles of carbon
(IV) oxide in soft drinks. (ii) Explain the observation made when a bottle containing a soft drink is opened. (iii) Carbon (IV) oxide dissolves slightly in water to give an acidic solution. Give the formula of the acid. (b) Zinc oxide can be obtained by heating zinc nitrate. A student heated 5.76 g of zinc nitrate. (i) Write an equation for the reaction that occurred. (ii) Calculate the total volume of gases produced. (Molar gas volume is 24 dm3; Zn = 65.4; O = 16.0; N = 14.0). (iii) Identify the element that is reduced when zinc nitrate is heated. Give a reason.
An electric current was passed through several substances and the results obtained recorded in the table below.
Which of these substance is likely to be
a)Magnesium b) Hexane c) lead (II) bromide ?
ANSWERS
(a) State one source of alkanes.
(b) Ethane gas was reacted with 1 mole of bromine gas. State one observation made during this reaction.
ANSWERS
(a) Sources of alkanescrude oil/petroleum natural gas/biogas
(b) The brown/red/orange/yellow colour of bromine is discharged/discoloured
(a) Describe how carbon (IV) oxide can be distinguished from Carbon II Oxide using calcium hydroxide solution.
(b) What is the role of carbon (IV) oxide in fire extinguishing?
ANSWERS
(a) Bubble the gases in calcium hydroxide solution. Carbon (II) Oxide does not react while Carbon (IV) Oxide forms a white precipitate.
(b) Carbon (IV) Oxide cuts the supply of oxygen
A hydrocarbon contains 14.5% of hydrogen. If the molar mass of the hydrocarbon is 56, determine the molecular formula of the hydrocarbon.
(C = 12.0; H = 1.0)
Starting with barium nitrate solution, describe how a pure sample of barium carbonate can be prepared in the laboratory.
ANSWERS
The graph below is a cooling curve for water. Study it and answer the questions that follow
(a) Explain what happens to the molecules of water in the region BC in terms of kinetic theory.
(b) In what state is the water in the region DE?
ANSWERS
The molecules of water are
(a) Loosing heat . The kinetic energy decreases and the molecules move closer to each other (b) Solid state
The table below is part of the periodic table. The letters are not the actual symbols of the elements. Study it and answer the questions that follows.
a) Select an element which is stored in paraffin in the laboratory
(b) How do the ionic radii of E and I compare? Explain
ANSWERS
(a) Element stored under paraffin G
(b) E is smaller than I. E has two energy levels while I has 3 energy levels.
Study the flow chart below and use it to answer the questions that follows
a) Name process T
b) Give the formula of W. c) State two uses of X
Describe how samples of lead (II) sulphate, ammonium chloride and sodium chloride can be obtained from a mixture of the three.
ANSWERS
Given that the E° of Cu(s) /Cu2+(aq) is +0.34 V and that of Zn (s)/Zn2+(aq) is —0.76 V, draw a labelled diagram of zinc and copper electrochemical cell. (3 marks)
During laboratory preparation of carbon(IV) oxide gas, dilute hydrochloric acid was added to substance L in a conical flask.
Study the information in Table 3 and use it to answer the questions that follow.
Use the information in Table 2 to answer the questions that follow.
(a) State what is meant by heat of reaction. (1 mark)
(b) Calculate the heat change when one mole of methane reacts completely with excess chlorine in the presence of UV light. (2 marks)
The heat of solution and hydration energy of potassium chloride is —17.2kJ and —689kJ respectively. Calculate the lattice energy of potassium chloride. (2 marks)
(a)Complete the following table. (2 marks)
(b) Explain why a solution of ammonia in methylbenzene has no effects on red litmus paper while in aqueous ammonia red litmus paper turns blue. (1 mark)
A crystal of iodine, heated gently in a test tube gave off a purple vapour.
(a) Write the formula of the substance responsible for the purple vapour. (b) What type of bond is broken when the iodine crystal is heated gently? (c) State one use of iodine.
ANSWERS
(a)Formula of Iodine I2
(b)Weak Van der Waals (c)Antiseptic
A radioactive substance weighing M kg took 1900 years for the original mass to reduce to 15 kg. Given that the half life of the radioactive substance is 380 years;
(a) Determine the original mass of the radioactive substance. (b) State two uses of radioactivity in medicine. .
Study the standard electrode potentials in the table below and answer the questions that follow.
(a) Which of the metals is the strongest reducing agent?
(b) What observations will be made if a silver coin was dropped into an aqueous solution of copper (II) sulphate? Explain.
ANSWERS
(a) Calcium
(b) No observable change silver is below copper in the reactivity series so it cannot displace it.
(a) One of the allotropes of sulphur is rhombic sulphur, name the other allotrope.
(b) Concentrated sulphuric (VI) acid reacts with ethanol and copper. State the property of the acid shown in each case. (i) Ethanol .................... (ii) Copper ....................
ANSWERS
(a) Monoclinic sulphur /Beta sulphur! Prismatic sulphur
(b) (i) Dehydrating property (ii) Oxidising property
The flow chart below shows various reactions of aluminium metal. Study it and answer the questions that follow
a) i) Other than water, name another reagent that could be R
ii) Write the formula of reagent Q b) Write an equation or the reaction in step 5.
Given the following substances: wood ash, lemon juice and sodium chloride.
(a) Name one commercial indicator that can be used to show whether wood ash, lemon juice and sodium chloride are acidic, basic or neutral. b) Classify the substances in 15(a) above as acids, bases or neutral
ANSWERS
(a) Universal indicator / litmus paper
(b) Acid, base, neutral.
The table below shows behaviour of metals R, X, Y and Z. Study it and answer the questions that follow:
a) Arrange the metals in the order of reactivity starting with the most reactive
b) Name a metal which is likely to be i X ii Y
ANSWERS
(a) Reactivity series starting with the most reactive
X R Z Y (b) X could be potassium Y could be copper |
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