KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
In an experiment to study the rate for reaction between duralumin (an alloy of aluminium, magnesium and copper) and hydrochloric acid, 0.5g of the alloy were reacted with excess 4M hydrochloric acid. The data in the table below was recoded.
Use it to answer the questions that follow. a) i) On the grid provided, plot a graph of total volume of gas produced (vertical axis) again time. ii) From the graph, determine the volume of gas produced at the end of 2 ½ minutes. b) Determine the rate of reaction between the 3rd and 4th minute. c) Give a reason why some solid remained at the end of the experiment d) Given that 2.5cm3 of the total volume of the gas was from the reaction between magnesium and aqueous hydrochloric acid, calculate the percentage mass of aluminium present in 0.5g of the alloy. (Al = 27.0 and Molar gas volume = 24,000cm3 at 298k) e) State two properties of duralumin that make it more suitable than aluminium in aeroplane construction.
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a) In which homologous series do the following compounds belong i) CH3CC ii) CH3CH2COO
b) Raw rubber is heated with sulphur in the manufacture of natural rubber.
i) What is the name given to the process ii) Why is the process necessary?
c) Study the scheme given below and answer the questions that follow
i) Write an equation for the reaction between propane – 1 – 0 / and potassium metal.
ii) Name processes I and II I II iii) Identify the products A and B iv) Name one catalyst used in process II v) Draw the structural formular of the repeating unit in the polymer C. d) State two industrial uses of methane.
a) Study the standard electrode potentials do the half – cells given below and
answer the questions that follow. (The letters do nor represent the actual symbols of the elements.)
i) Identify the strongest oxidizing agent. Give a reason for your answer.
ii) Which two half – cells would produce the highest potential difference when combined? iii) Explain whether the reaction represented below can take place. b) 100cm3 of 2M sulphuric acid was electrolysed using the set – up represented by the diagram below.
i) Write an equation for the reaction that produces gas L.
ii) Describe how gas K can be identified iii) Explain the difference in : I The volume of the gases produced at the electrodes. II Brightness of the bulb if 100cm3 of 2M ethanoic acid was used in place of sulphuric acid.
(a) Give the systematic names for the following compounds
(b) Study the flow chart below and use it to answer the questions that follow
(i) Identify the organic compound K
(ii) Write the formula of M (iii) Give one reagent that can be used in (a) Step I (b) Step II (iv) Write the equation of the reaction in step III (c) The structure below represents a type of a cleaning agent
Describe how the cleansing agent removes grease from a piece of cloth
(a) distinguish between a neutron and proton
(b) What is meant by a radioactive substance? (c) State two dangers associated with radioactive substance in the environment
(i) What is the atomic
a. Mass of Y b. Number of Y (ii) What name is given to the type of reaction undergone by the isotopes of hydrogen? (e)(i) What is meant by half-life of a radioactive substance (ii) 288 g of a radioactive substance decayed to 9 g in 40 days. Determine the half-life of the radioactive substance
(a) describes one method that can be used to distinguish between sodium sulphate and sodium hydrogen sulphate.
b) Describe how a pure sample of lead (II) sulphate can be prepared in the laboratory starting with lead metal c) Study the flow chart below and answer the questions that follow:
i) Write an equation for the reaction in:
I step II; II step IV ii) State the observation made in step III. Explain. iii) Name another substance that can be used in step V.
ANSWERS
(a)Test the acidity using a litmus pager. There will be no change on litmus when dipped into a solution of sodium sulphate . The litmus paper turns to red when dipped into a solution of sodium hydrogen sulphate .
OR Add a solid carbonate to each solution. No effervescence observed when the carbonate is added to a solution of sodium sulphate. Effervescence is observed when the carbonate is added to a solution of sodium hydrogen sulphate. (b)Add dilute nitric acid to lead to form a soluble salt, Pb(NO3)2, add a soluble salt, Na2SO4. Then dry the salt between filter papers . (c)(i) NH4 NO3 → N2O + 2H2O II 2Fe(OH)3(S) → Fe2O3(s) + 3H2O(l) (ii) The colour changes from pale green to brown . The iron (II) is oxidised to iron (III) chloride by hydrogen peroxide (iii) Carbon monoxide
(a) the set below can be used to produce sodium hydroxide by electrolyzing brine
(i) Identify gas Y
(ii) Describe how aqueous sodium hydroxide is formed in the above set-up (iii)One of the uses of sodium hydroxide is in the manufacturing of soaps state one other use of sodium hydroxide (b).study the information given in the table below and answer the question that follows
(i) Construct an electrochemical cell that will produce the largest emf
(ii) Calculate the emf of the cell constructed in(i) above (iii) Why is it not advisable to store a solution containing E+ ions in a container made of H?
ANSWERS
(a)(i)Gas Y is chlorine
(ii) sodium and hydrogen ions migrate to the cathode . The hydrogen ions are preferentially discharged, liberating hydrogen gas. chlorine and hydroxide ions migrate to the anode . The chloride ions are preferentially discharged liberating chlorine gas. the sodium ions migrate to the cathode through the membrane . the sodium ions combine with the hydroxide ions to form sodium hydroxide . (iii) Glass making/paper manufacture (1), unclogging of drains, etching NaClo3, Purification of bauxite.
(a) The diagram below shows the frasch process used for extraction of sulphur
Use it to answer the question that follows
(i) Identify X
(ii) Why is it necessary to use superheated water in this process (iii) State two physical properties of sulphur that makes it possible for it to be extracted by this method (b) The diagram below shows part of the process in the manufacture of sulphuric (VI) acid. Study it and answer the questions that follow
(I) Write an equation for the formation of sulphur (IV) oxide from sulphur
(II) What is the role of concentrated sulphur (VI) acid in chamber A? (III) Name two catalysts that can be used in the catalytic chamber B. (IV) State two roles of the heat exchanger (c) Explain one way in which sulphur (IV) oxide is a pollutant (d).what observation will be made when a few drops of concentrated sulphuric (VI) acid are added to crystals of sugar? Explain your answer
ANSWERS
(a)(i)Hot compressed air
(ii)To melt the sulphur and maintain it in molten state (iii)low melting point of sulphur - insolubility of sulphur in water - less dense than water (b)(i)S + O2 → SO2 (ii)To dry the SO2 and air (iii)Vanadium (v) oxide and platinum or titanium (iv)it provides the reactants (SO2 and O2) with enough energy to react - it removes heat from the product hence preventing decomposition or conserves heat, or recycles heat or reduces cost of production. (c)- contributes to acid rain which corrodes buildings OR - causes aquatic solutions to be acidic hence affecting aquatic life etc. - poisonous/toxic (d)Turns black conc H2SO4 removes hydrogen and oxygen from the sugar molecule leaving only carbon which is black . Dehydration of sugar forms carbon which is black.
(a) (i) what is meant by the term Enthalpy of formation?
(ii) The enthalpies of combustion of carbon, methane and hydrogen are indicated below:
(i) Draw an energy cycle diagram that links the enthalpy of formation of methane to enthalpies of combustion of carbon, hydrogen and methane
(ii) Determine the enthalpy of formation of methane (b) An experiment was carried out where different volumes of dilute hydrochloric acid and aqueous sodium hydroxide both at 25°C were mixed and stirred with a thermometer. The highest temperature reached by each mixture was recorded in the table below
(i) On the grid provided. plot a graph of highest temperature (vertical axis) against volume of hydrochloric acid ( horizontal axis)
(ii) Using your graph , determine the (a) Highest temperature reached (b) Volume of acid and base reacting when highest temperature is reached
(iii) Calculate the amount of heat liberated during the neutralization process .(specify heat capacity is 4.2 j g -1 k-1 and the density of solution is 1.0 g cm-3)
(c) The molar enthalpy of neutralization between hydrochloric acid and ammonia solution was found to be -52.2 kJ mol-1, while that of hydrochloric acid and sodium hydroxide was – 57.1 Kj mol-1. Explain the difference in these values.
ANSWERS
(a)(i)This is the heat absorbed or evolved when one mole of any substance is formed from its constituent elements in their normal states.
(c)The molar heat of neutralisation between a strong acid and a weak base is low because some of the heat is used to ionise (1) the weak base before neutralization.
For strong acid and strong base they are completely ionised.
The grid given below represents part of the periodic table. Study it and answer the questions that follow. The letters do not represent the actual symbol of the element
(i) Select a letter which represents an element that looses electrons most readily. Give a reason for your answer.
(ii) Explain why the atomic radius of P is found to be smaller than that of N (iii) Element M reacts with water at room temperature to produce 0.2 dm3 of gas. Determine the mass of M which was reacted with water. (molar gas volume at room temperature is 24 dm3 , relative atomic mass of M=7 (b) Use the information in the table below to answer the question that follows. (The letters are not the symbols of the elements)
Identify a letter which represents an element in the table that could be calcium, carbon or sculpture. Give reasons in each case.
(i) Calcium: Reason (ii) Carbon Reason (iii)Sulphur: Reason
ANSWERS
(a)(i)R - it has the largest atomic radius with the weakest nuclear attraction for outermost electron
(ii)Across the period the atomic radius decreases due to the increase in nuclear attraction Number of electrons in P is greater than in H
(b)(i) W - forms a basic oxide which forms an ionic bond
(ii)Y - the oxide is gaseous that forms a neutral solution (iii)U - the oxide is solid at room temperature, which is acidic with covalent bond
a) The diagram below is part of set up used to prepare and collect dry chlorine gas.
i) Complete the diagram to show how a dry sample of chlorine gas can be collected.
ii) Name another substance and condition that can be used instead of manganese (VI) oxide. iii) Write an equation for each of the following; I. chlorine gas reacting with iron II. chlorine gas reacting with hot concentrated sodium hydroxide solution. b) An oxide of chlorine of mass 1.83g was found to contain 1.12g of oxygen. Determine the empirical formula of the oxide (O = 16.0; Cl = 35.5). c) Other than the manufacture of weed killers, name two other uses of chlorine.
The flow chart below shows a sequence of reactions involving a mixture of two salts, mixture M. Study it and answer the questions that follow.
a) Write the formula of the following;
i) anion in solid Q ii) the two salts present in mixture M. b) Write an ionic equation for the reaction in step (VI) c) State and explain the observations made in step (V). d) i) Starting with Lead (II) oxide, describe how a pure solid sample of lead sulphate can be prepared in the laboratory. ii) How can one determine whether the lead sulphate prepared is pure?
ANSWERS
(c)The solution changes from blue to colourless and a brown solid is formed.
The magnesium which is above copper in the reactivity series displaces the copper ions from the solution. Apparatus become warm. The reaction is exothermic. (d)(i) Add nitric (V) acid to lead oxide, filter add a soluble sulphate/ sulphuric acid to the filtrate . Filter and wash residue with distilled water to remove traces of the filtrate, then dry residue between i. filter papers /oven. (ii) Determine the melting point, if it is pure the melting point will be constant.
a) The set up below was used to investigate the products formed at electrodes during electrolysis of aqueous magnesium sulphate using inert electrodes. Use it to answer the questions that follow.
i) During the electrolysis, hydrogen gas was formed at electrode Y. identify the anode. Give a reason for your answer.
ii) Write the equation for the reaction with takes place at electrode X. iii) Why is the concentration of magnesium sulphate expected to increase during electrolysis? iv) What will be observed if red and blue litmus papers were dipped into the solution after electrolysis? b) During electrolysis of magnesium sulphate, a current of 0.3A was passed for 30 minutes. Calculate the volume of gas produced at the anode.(Molar gas volume = 24dm3; 1 Faraday = 96,500C.). c) State two applications of electrolysis.
The factors which affect the rate of reaction between lead carbonate and dilute nitric (V) acid were investigated by carrying out three experiments;
a) Other than concentration , name the factor that was investigated in the experiments.
b) For each experiment, the same volume of acid (excess) and mass of lead carbonate were used and the volume of gas liberated measured with time. i) Draw a set up that can be used to investigate the rate of reaction for one of the experiments. ii) On the grid provided, sketch the curves obtained when the volume of gas produced was plotted against time for each of the three experiments and label each as 1, 2 or 3.
iii) Write an equation for the reaction that took place.
c) If the experiments were carried out using dilute hydrochloric acid in place of dilute nitric (V) acid, the reaction would start, slow down and eventually stop. Explain these observations. d) A solution of bromine gas in water is an example of a chemical reaction in a state of balance. The reaction involved is represented by the equation below.
State and explain the observation made when hydrochloric acid is added to the mixture at equilibrium.
In the laboratory, small quantities of nitric (V) acid can be generated using the following set up. Study it and answer the questions that follow.
a) i) Give the name of substance R.
ii) Name one other substance that can be used in place of sodium nitrate. iii) What is the purpose of using tap water in the set up above? b) Explain the following; i) It is not advisable to use a stopper made of rubber in the set-up ii) the reaction between copper metal with 50% nitric (V) acid in an open test-tube produces brown fumes. c) i) Nitrogen is one of the reactants used in the production of ammonia, name two sources of the other reactant. ii) A factory uses nitric (V) acid and ammonia gas in the preparation of a fertilizer. If the daily production of the fertilizer is 4800kg; calculate the mass of ammonia gas used in kg. (N = 14.0; O = 16.0; H = 1.0) iii) State two other uses of nitric (V) acid other than the production of fertilizers.
ANSWERS
(a) (I) Concentrated /sulphuric (VI) acid.
(ii) Potassium nitrate (iii) To condense the fumes or vapour of nitric (V) acid into liquid (b) (i) Nitric acid (V) will corrode the rubber (ii) The reaction produces nitrogen monoxide (colourless) which is oxidised by oxygen from the air to form nitrogen(IV) oxide. (c)(i) Water Alkanes Biogas Water gas
The grid below is part of the periodic table. Use it to answer the questions that follow. (The letters are not the actual symbols of the elements)
a) Which is the most reactive non-metallic element shown in the table? Explain.
b) i) Write the formula of the compound formed when element A reacts with element B. ii) Name the bond type in the compound formed in b (i) above. c) i) What is the name given to the group of elements where C, G and H belong? ii) Write an equation for the reaction that occurs when C in gaseous form is passed through a solution containing ions of element H. d) The melting points of elements F and G are 1410°C and -101°C respectively. In terms of structure and bonding, explain why there is a large difference in the melting points of F and G. e) D forms two oxides. Write the formula of each of the two oxides. f) J is an element that belongs to the 3rd period of the periodic table and a member of the alkaline earth elements. Show the position of J in the grid.
a) Draw the structural formula for all the isomers of C2H3CL3
b) Describe two chemical tests that can be used to distinguish between ethane and ethane. c) The following scheme represents various reactions starting with propan-1-ol. Use it to answer the questions that follow.
i) Name one substance that can be used in step I.
ii) Give the general formula of X. iii) Write the equation for the reaction in step IV. iv) Calculate the mass of propan-I-ol which when burnt completely in air at room temperature and pressure would produce 18dm3 of gas. (C = 12.0; O = 16.0; H = 1.0; Molar gas volume = 24dm3)
ANSWERS
(a) A student was supplied with a colourless liquid suspected to be water
The flow chart below shows the various stages of water treatment. Study it and answer the questions that follow
II Addition of sodium hypochlorite (c) It was confirmed that magnesium sulphate was present in the tap water
(a) The following diagrams show the structures of two allotropes of carbon. Study them and answer the questions that follow
(i) Name allotrope
M N (ii) Give one use of N (iii) Which allotrope conducts electricity? Explain
(b) In an experiment, carbon dioxide gas as passed over heated charcoal and the gas produced collected as shown in the diagram below
(i) Write an equation for the reaction that took place in the combustion tube
(ii) Name another substance that can be used instead of sodium hydroxide (iii) Describe a sample chemical test that can be used to distinguish between carbon dioxide and carbon monoxide (iv) Give one use of carbon monoxide
(a) Give the names of the following compounds
Name the type of bromination reaction that takes place in: (i) and (ii)
(d) The polymerization of tetra flouroathene (C2H4) is similar to that of ethane ( C2H4)
(e) State any two advantages that synthetic polymers have over natural polymers
(a)
(b) A sample of hydrogen chloride gas was dissolved in water to make 250cm3 of solution required 46 cm3 of 11.0M Sodium hydroxide for complete neutralization.
​(a) The grid given below represents part of the periodic table. Study it and answer the questions that follow. (the letters do not represents the actual symbol of the elements)
​(b) Study the information in the table below and answer the questions that follow (the letters do not represent the actual symbol of the substances)
II. By downward displacement of air? (Density of air is 1.29 x 10-3g/cm3 at room temperature. Related Chemistry Questions and Answers on Chemical Families Form 2 Level
​The flow chart below illustrate the industrial extraction of lead metal. Study it and answer the questions that follow
(a)
(c) State one use of lead other than the making of lead pipes Related Chemistry Questions and Answers on Metals Form 4 Level
1 (a) The diagram below represents a mercury cell that can be used in the industrial manufacture of sodium hydroxide. Study it and answer the question that follow
Study the information in the table below and answer the questions that follow. The letters do not represent the symbols of the elements.
a) Write the electrons arrangement for the atom formed by elements and M and Q
b) Select an element which is
d) Element R lodes its outermost electron more readily than I. Explain e) Using dots(.) and crosses (x) to represent outermost electrons show bonding in the compound formed elements N and Q. f) Explain why the melting point elements M is higher than that of element . g) Describe how a solid mixture of sulphate of R and lead sulphate can be separated into solid samples. |
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