KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
a) The flow chart below shows a sequence of reactions starting with.
Study and answer the questions that follow.
Cu = 63.5, Fe = 56.0
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a) The diagram below shows a set –up used by as a student in an attempt to prepare and collect oxygen gas
c) The reaction between sulphur dioxide and oxygen to form trioxide in the contact process in exothermic. Factory manufacturing sulphuric acid by contact process produces 350kg of sulphur trioxide per day (conditions) for the reaction catalyst. 2 atmospheres pressure and temperatures between. (400 – 5000C) i) What is meant by an exothermic reaction? ii) How would the yield per day of sulphur trioxide be affected Temperatures lower than 40000C are used? Explain.
a) When an organic compound Y is reacted with aqueous sodium carbonate, it produces carbon dioxide reacts with propanol to form a sweet smelling compound Z whose formula is.
c) The scheme below was used to prepare a cleaning agent. Study and answer the questions that follow.
i) What name is given to the type of cleaning agent prepared by the method shown in the scheme?
ii) Name one chemical substance added in step II iii) What is the purpose of adding the elements substance names in C(ii) above. iv) Explain how an aqueous solution of the cleansing removes oil from utensils during washing.
The set – up below was used during the electrolysis of aqueous magnesium sulphate using inert electrodes
i) Name a suitable pair of electrodes for this experiment ii) Identify the ions and cations in the solution iii) On the diagram label the cathode iv) Write ionic equations for the reactions that took place at the anode. v) Explain the change that occurred to the concentration of magnesium sulphate solution during the experience. vi) During the electolysis a current of 2 amperes was passed through the solution for 4 hours. Calculate the volume of the gas produced at the anode.(1 faraday 96500 coulombs and volume of a gas at room temperature is 24000cm3) vii) One of the uses of electrolysis is electroplating What is meant by electroplating? Give tow reasons why electroplating is necessary.
The table below gives the volume of the gas provided when different volumes of 2M hydrochloric were reacted with 0.6g of magnesium powder at room temperature
(a) Write an equation fro the reaction between magnesium and hydrochloric acid
(b) On the grid provided plot a graph of the volume of gas produced (vertical axis), against the volume of acid added (Note the reaction comes to completion, the volume of the gas produced directly proportional to completion, the acid added). From the graph determine c)
e) Given that one mole of the gas occupied 24000cm3 at room temperature.
(a) What is meant by molar heat of combustion?
(b) State the Hess's Law. c) Use the following standard enthalpies of combustion of graphite, hydrogen and enthalpy of formation of propane.
(i) Write the equation for the formation of propane.
(ii) Draw an energy cycle diagram that links the heat of formation of propane with its heat of combustion and the heats of combustion of graphite and hydrogen. (iii) Calculate the standard heat of combustion of propane. Other than the enthalpy of combustion, state one factor which should be considered when choosing a fuel. (e) The molar enthalpies of neutralization for dilute hydrochloric acid and dilute nitric (V) acid are -57.2kJ/mol while that of ethanoic acid is -55.2kJ/mol. Explain this. observation.
ANSWERS
(a) The amount of heat liberated when one mole of a substance is burnt in excess Oxygen.
(b) The heat evolved are absorbed in a chemical change is the same whether the change occurs in one step or through many steps.
(d) cost
effect on environment availability storage (e) Ethanoic acid is a weak acid therefore heat is used to ionize it before neutralization occurs . It value is therefore lower than that of hydrochloric acid which is fully ionized
(a) Study the flowchart below and answer the questions that follows;
(i) I What observation will be made in Step I
II Describe a chemical test that can be carried out to show the identity of compound C (ii) Give the names of the following I E II substance D (iii)Give the formula of substance B . (iv) Name the type of reaction that occurs in: I Step (II) II Step (IV) (v) Give the reagent and conditions necessary for Step (VI). Reagent: Conditions (b) (i) Name the following structure.
(ii) Draw the structure of an isomer of pentene.
ANSWERS
(a) (i) I The potassium permanganate is decolorized or changes from purple to colourless.
II C is a ethanoic acid (carboxylic acid) Add sodium carbonate, you will see effervescence, test gas evolved with lime water, it will form a white precipitate. (ii) I Polyethene II Substance D - sodium ethoxide
(a) Other than their location in the atom, name two other differences between an electron and a proton.
(b) the table below gives the number of electrons ,protons and neutrons in particles A,B, C , D, E, F and G
(i) Which particle is likely to be a halogen?
(ii) what is the mass number of E (iii) write the formula of the compound formed when E combines with G iv) Name the type of bond formed in (iii) above. (v) How does the radii of C and E compare ? Give reason. (vi) Draw a dot (.) and cross(x) diagram for the compound formed between (vii) Why would particle B not react with particle D?
ANSWERS
(a)- electron has I mass while proton has mass of one mass unit. 1840
- proton is positively charged while electron is negatively charged.
(iv)Ionic bond or electrostatic
(v)E has a smaller atomic radius than C E has more protons than C : nuclear attraction stronger.
(vii)Particle B is inert with a stable electronic configuration will not react.
(a) When excess calcium metal was added to 50 cm3 of 2 M aqueous copper (II) nitrate in a beaker, a brown solid and bubbles of gas were observed.
(i) "Write two equations for the reactions which occurred in the beaker. (ii) Explain why it is not advisable to use sodium metal for this reaction.
(b) Calculate the mass of calcium metal which reacted with copper (II) nitrate solution. (Relative atomic mass of Ca = 40)
(c) The resulting mixture in (a) above was filtered and sodium hydroxide added to the filtrate dropwise until in excess. What observations were made? (d) (i) Starting with calcium oxide, describe how a solid sample of calcium carbonate can be prepared. (ii) Name one use of calcium carbonate
ANSWERS
(c)A white precipitate is formed which is insoluble in excess.
(d) (I) Add dilute nitric (V) acid to calcium oxide to form the soluble salt calcium nitrate. Add sodium carbonate (another soluble salt) to form insoluble. Calcium Carbonate and sodium nitrate . Filter out the calcium carbonate, wash it with distilled water to remove traces of sodium nitrate and dry between filter papers (ii) Manufacture of cement Manufacture of sodium carbonate.
(a) Ethanol can be manufactured from ethene and steam as shown in the equation below:
Temperature and pressure will affect the position of equilibrium of the above reaction. Name the other factor that will affect the position of equilibrium of the above reaction.
(b) The data in the table below was recorded when one mole of ethene was reacted with excess steam. The amount of ethanol in the equilibrium mixture was recorded under different conditions of temperature and pressure. Use the data to answer the questions that follow.
(i)State whether the reaction between ethene and steam is exothermic or endothermic.
Explain your answer. (ii) State and explain one advantage and one disadvantage of using extremely high pressure in this reaction. I Advantage II disadvantage (c) In an experiment to determine the rate of reaction between calcium carbonate and dilute hydrochloric acid, 2g of calcium carbonate were reacted with excess 2 M hydrochloric acid, The volume of carbon (IV) oxide evolved was recorded at regular intervals of one minute for six minutes. The results are shown in the table below.
(i) plot a graph of time in minutes on the horizontal axis against volume of carbon (IV) oxide on the vertical axis.
(ii) determine the rate of reaction at 4 minutes
ANSWERS
(a) Increase or change in amount of reagent either reactants or products.
(Concentration). (b) (i) Exothermic increase in temperature from 250 - 350 at constant pressure the amount of ethanol formed at equilibrium decreases. (ii) I Advantage - it would increase the yield of ethanol ; since increase in pressure will favour side with less moles i.e. the products. II Disadvantage - it would mean investment in equipment to withstand the high pressure and would be expensive.
The set-up below was used by a student to investigate the products formed when aqueous copper (II) chloride was electrolyzed using carbon electrodes.
(a) (i) Write the equation for the reaction that takes place at the cathode.
(ii) Name and describe a chemical test for the product initially formed at the anode when a highly concentrated solution of copper (II) chloride is electrolysed. (iii) How would the mass of the anode change if the carbon anode was replaced With copper metal? Explain. (b) 0.6 g of metal B were deposited when a current of 0.45A was passed through an electrolyte for 72 minutes. Determine the charge on the ion of metal B. (Relative atomic mass of B = 59, 1 Faraday = 96 500 coulombs) (c) The electrode potentials for cadmium and zinc are given below:
Explain why it is not advisable to store a solution of cadmium nitrate in a container made of zinc
The flow chart below shows some of the processes involved in large scale production of sulphuric (VI) acid. Use it to answer the questions that follow.
a) Describe how oxygen is obtained from air on a large scale
(b) (i) Name substance A. (ii)Write an equation for the process that takes place in the absorption chamber. (c) Vanadium (V) oxide is a commonly used catalyst in the contact process. (i) Name another catalyst which can be used for this process. (ii) Give two reasons why vanadium (V) oxide is the commonly used catalyst. (d) State and explain the observations made when concentrated sulphuric (VI) acid is added to crystals of copper (II) sulphate in a bearer. (e) The reaction of concentrated sulphuric (VI) acid with sodium chloride produces hydrogen chloride gas. State the property of concentrated sulphuric (VI) acid , illustrated in this reaction. (f) Name four uses of sulphuric (VI) acid
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.
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)
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.
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
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) (a) The table below gives the solubilities of hydrated copper (II) sulphate in mol dm3 at different temperatures (i) On the grid provided, plot a graph of solubility of copper (II) sulphate (vertical axis) against temperature. (ii) From the graph, determine the mass of copper (II) sulphate deposited when solution is cooled from 700C to 400C. (Molar mass of hydrated copper (II) sulphate = 250g) (b) In an experiment to determine the solubility of sodium chloride, 5.0cm3 of a saturate solution of sodium chloride weighing 5.35g were placed volumetric and diluted to a total volume of 250cm3. 25.0cm3 of the dilute solution chloride completely reacted with 24cm3 of 0.1M silver nitrate solution. AgNO3(aq) + NaCI(aq) → AgCl(s) + NaNO3(aq) Calculate: (i) Moles of silver nitrate in 24cm3 of solution (ii) Moles of sodium chloride in 25.0cm3 of sodium (iii) Moles of sodium chloride in 250cm3 of solution (iv) Mass of sodium chloride in 5.0cm3 of saturated sodium chloride Solution (Na = 23.0, CI = 35.5) (v) Mass of water in 5.0cm3 of saturated solution of sodium chloride (vi) The solubility of sodium chloride in g/100 water
Iron is obtained from haematite using a blast furnace shown if figure 5 below.
a) Four raw materials are required for the production of iron. Three of these are iron oxide, hot air and limestone
Give the name of the fourth raw material b) Write an equation for the reaction in which carbon (IV) oxide is converted into carbon (II) oxide. c) Explain why the temperature in the region marked Y is higher than that of the incoming hot air. d) State one physical property of molten slag other than density that allows it to be separated from molten iron as shown in figure 5. e) One of the components of the waste gases is Nitrogen (IV) oxide describe the adverse effects it has on the environment. f) Iron from the blast furnace contains about 5% carbon i) Describe how the carbon content is reduced. ii) Why is it necessary to reduce the carbon content?
ANSWERS
(a) Coke/ coal/ Charcoal/ Carbon
(b) C(s) + CO2 (g) → 2 CO(g) (c) The reaction between coke/ coal and the hot air is highly exothermic (d) Slog is immiscible with molten iron (e) Nitrogen (iv) oxide gas forms acid rain. Which corrodes metallic materials and destroys vegetation the environment. (f) (i) By passing/ blowing oxygen into molten iron which converts carbon into carbon (iv) Oxide (ii) To increase the tensile strength/ making the iron less brittle/ making it more malleable / making it more ductile.
a) Study the table below and complete it. (W-1 and X4+ are not the actual symbols of the ions).
b) State the observation that would be made in the following tests to distinguish between:
i) Sodium and copper burning pieces of each in air. ii) Sodium and Magnesium by placing small pieces of each in cold water which contains two drops of phenolphalein. c) The atomic numbers of Na and Mg are 11 and 12 respectively. Which of the elements has a higher ionization energy? Explain. d) Naturally occurring uranium consists of three isotopes which are radioactive.
i) Which of these isotopes has the longest half-life? Give a reason
ii) Calculate the relative atomic mass of uranium
(iv)State one use of radioactive isotopes in the paper industry
ANSWERS
(b) (i) Sodium burns with a yellow flame & yellow white/ solid powder is formed while copper burn with a blue green flame & black powder/ silic is formed.
(ii) Sodium darts on the surface of water / rapid fast effervescence (fast production of bubbles; solution becomes pink immediately. Magnesium sinks in water/ slow (production of bubbles) effervescence/ solution becomes pink gradually. (c) Magnesium it has a higher nuclear charge which pulls outer electrons more strongly
(a)Figure 3 show the changes that take place between states of matter. Some of them have been identified and others labelled.
i) Give the names of the processes
I H II G ii) Name one substance that can undergo process F when left in an open container in the laboratory. iii) The process J is called deposition. Using water as an example, write an equation that represents the process of deposition. b) Figure 4 shows the beating curve for water.
i) Give the names of the intermolecular forces of attraction in the segments;
I MN II RS ii) The heats of fusion and vaporization of water are 334.4 Jg-1 and 1159.4 Jg-1 respectively. I Explain why there is a big difference between the two. II How is the difference reflected in the curve? c) Coal, oil and natural gas are major sources of energy. They are known as fossil fuels. Hydrogen is also a source of energy. i) State and explain two reasons why hydrogen is a very attractive fuel compared to fossils. ii) State one disadvantage of using hydrogen fuel instead of fossil fuels.
ANSWERS
(a)
(i) I. Condensation II. Melting (ii) Iodine, Benzoic acid, Camphos, Dry Ice. Solid CO2 Naphthalene (iii) H2O(g) →H2O(g) (b) (i) Van des waals and hydrogen bonding II Van des waals forces (ii)I. The separation distance is smaller during fusion than during vaporization hence requires much lower energy than in vaporization and vice versa. II. Heating time NP is far much less than heating time in QR/ Heating time (c) (i) Hydrogen burns to produce steam which is a non pollutant/ does not cause pollution to the environment Hydrogen has a high energy content hence very small amount produce a lot of heat energy Hydrogen is renewable hence cannot be exhausted/ used completed. (ii) It can easily explore when burning/ highly flammable unlike fossils fuels expensive.
a) the schematic diagram shows part of the Solvay process used for the manufacture of sodium carbonate.
i) Explain how the sodium chloride required for this process is obtained from sea water.
ii) Two main reactions take place in UNIT I . The first one is the formation of ammonium hydrogen carbonate. I. Write an equation for this reaction II. Write an equation for the second reaction iii) State how the following are carried out: I Process I II) Process II iv)In an experiment to determine the percentage purity of the sample of sodium carbonate produced in the Solvay process, 2.15 g of the sample reacted completely with 40.0cm3 of 0.5 M sulphuric acid. I calculate the number of moles of sodium carbonate that reacted. II Determine the percentage of sodium carbonate in the sample. (Na= 23.0, C= 12.0, O = 16.0) b) Name two industrial uses of sodium carbonate
The set-up below (figure 2) was used to electrolyse a bromide of metal D DBr2
i) Write equation for the reactions at the
I cathode II anode ii) The electrodes used in the experiment were made of carbon and metal D. which of the two electrodes was used as the anode? Give a reason. iii) Give a reason why this experiment is carried out in a fume cupboard. iv) When a current of 0.4A was passed for 90 minutes, 2.31 g of metal D were deposited. I Describe how the amount of metal D deposited was determines. II Calculate the relative atomic mass of metal D. (I Faraday = 96500 coulombs) |
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