KCSE CHEMISTRY QUESTIONS AND ANSWERS PER TOPIC
a) Draw the structures of the following compounds:
i) 2- methylbut -2 ene; ii) heptanoic acid b) Describe a physical test that can be used to distinguish between methanol and hexanol. c) Use the flow chart below to answer the questions that follow.
i) Name: (I) the type of reaction that occurs in step II; (II) Substance B. ii) Give the formula of substance C. iii) Give the reagent and the conditions necessary for the reaction in step (IV)
ANSWERS
(b)
0 Comments
a) Two reagents that can be used to prepare chlorine gas are manganese (IV) oxide and concentrated hydrochloric acid.
i) Write an equation for the reaction. ii) Give the formula of another reagent that can be reacted with concentrated hydrochloric acid to produce chlorine gas. iii) Describe how the chlorine gas could be dried in the laboratory b) In an experiment, dry chlorine gas was reacted with aluminium as shown in figure 1.
i) Name substance A.
ii) Write an equation for the reaction that took place in the combustion tube. iii) 0.84 g of aluminium reacted completely with chlorine gas. Calculate the volume of chlorine gas used (Molar gas volume is 24dm3, Al = 27). iv) Give two reasons why calcium oxide is used in the set up.
Study the information given in the table below and answer the questions that follow. The letters do not represents the actual symbols of the elements
(a) Select the elements which belong to the same
(e) The aqueous sulphate of element W was electrolyzed using inert electrodes Name the products formed at the:
The flow chart below shows the industrial preparation of ammonia and the process used in the manufacture of some ammonium compounds. Study and answer the questions that follow
(a) Give the name of the
(c) Explain why it necessary to compress nitrogen and hydrogen in this process (d) Write an equation for the reaction which takes place in step 6 (e) Name the catalyst and the reagents used in step 3 Catalyst Reagent (f) Name compound Z1 (g) Give one commercial use of compound Z2
(a) An ore is suspected to contain mainly iron. Describe a method that can be used to confirm the presence of iron in the ore
(b) Excess carbon monoxide gas was passed over a heated sample of an oxide of iron as shown in the diagram below. Study the diagram and the data below it to answer the questions that follow.
Mass of empty dish = 10.98g
Mass of empty dish 4 oxide of iron = 13.30g Mass of empty dish 4 residue = 12.66g
(c) Corrosive is a destructive process in which iron which is converted into hydrated iron (III) oxide State:
(d) Explain why it is not advisable to wash vehicles using seawater
(a) The following equations represents two different types of reactions
(i) nC4H8(g) → (C4H8)n(s) (ii) C2H6(g) + CI2(g) → C2H5CI(I) + HCI(g) State the type of reaction represented by: (i) (ii) (b) The fermentation of glucose produces ethanol as shown in the equation below C2H12O6(aq) → 2CH3CH2OH(aq) + 2CO2(g)
(c) The molecular formula of a hydrocarbon is C6H14. The hydrocarbon can be converted into two other hydrocarbons as shown by the equation below (i) Name and draw the possible structural formula of X Name Structural formula (ii) State and explain the observation that would be made if a few drops of bromide water were added to a sample of X. (iii) Write an equation for the complete combustion of C3H8
The set – up below was used to prepare anhydrous chlorides of a number of elements in a laboratory where no fine cupboard was available. The chlorides were to be collected in flask
The following table shows the melting and boiling points of the chlorides that were prepared.
More Quiz
(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 In order to determine the molar of neutralization of sodium hydroxide, 100cm3 of 1M sodium hydroxide and 100cm3 of 1 M hydrochloric acid both at the same initial temperature were mixed and stirred continuously with a thermometer. The thermometer of the resulting solution was recorded after every 30 seconds until the highest temperature of the solution was attained. Thereafter the temperature of the solution was recorded for a further two minutes
(a)
I. What is the significance of point Y2? II. Explain why there is a temperature change between points; Y1 and Y2 Y3 and Y4 (iv) In the initial temperature for both solutions was 24.50C and the highest temperature attained by the mixture was 30.90C Calculate the: I. heat change for the reaction (specific heat capacity of the solution = 4.2Jg -1K-1 and the density of the solution = 1.0g/cm3 II. Molar heat of neutralization of sodium hydroxide (v) Explain how the value of the molar heat of neutralization obtained in this experiment would compare with the one that would be obtained if the experiment was repeated using 100cm3 of 1 Methanoic acid instead of hydrochloric acid. (b) On the grid provided below, draw an energy level diagram for the reaction between hydrochloric acid and sodium hydroxide
(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
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.
a) Write an equation to show the effect of heat on the nitrate of:
(i) Potassium b) The table below gives information about elements A1,A2,A3, and A4
(i) In which period of the periodic table is element A2? Give a reason
(ii) Explain why the atomic radius of: I A1 is greater than that of A2; II A4 is smaller than its ionic radius (iii) Select the element which s in the same group as A3 (iv) Using dots (.) and crosses(x) to represent outermost electrons. Draw a diagram to show the bonding in the compound formed when A1 reacts with A4
a) Biogas is a mixture of mainly carbon (IV) oxide and methane.
(i) Give a reason why biogas can be used as a fuel. (ii) Other than fractional distillation, describe a method that can be used to determine the percentage of methane in biogas. b) A sample of biogas contains 35.2% by mass of methane. A biogas cylinder contains 5.0 kg of the gas. Calculate the; (i) Number of moles of methane in the cylinder. (Molar mass of methane=16) (ii) Total volume of carbon (IV) oxide produced by the combustion of methane in the cylinder (Molar gas Volume=24.0 dm-3+ at room temperature and pressure). c) Carbon (Iv) oxide, methane, nitrogen (I) oxide and trichlorofluoromethane are green-house gases. (i) State one effect of an increased level of these gases to the environment. (ii) Give one source from which each of the following gases is released to the environment; I Nitrogen (i) oxide II Trichlorofluoromethane.
The diagram below shows the set up used in an experiment to prepare chlorine gas and react it with aluminium foil. Study it and answer the question that follow
(a) In the experiment, concentrated hydrochloric acid and potassium manganate (VII) were used to prepare chlorine gas. State two precautions that should be taken in carrying out this experiment.
(b) Write the formula of another compound that could be used instead of potassium manganate (VII) (c) Explain why it is necessary to allow the acid to drip slowly onto potassium manganate (VII) before the aluminium foil is heated. (d) State the property of the product formed in the combustion tube that makes it possible for it to be collected in the receiver (e) When 1.08g of aluminum foil were heated in a stream of chlorine gas, the mass of the product formed was 3.47 g Calculate the: (i) Maximum mass of the product formed if chlorine was in excess; (Al= 27; Cl = 35.5) (ii) Percentage yield of the product formed (f) Phosphorous trichloride is a liquid at room temperature. What modification should be made to set up if it is to be used to prepare phosphorous trichloride?
(a) The elements nitrogen, phosphorous and potassium are essential for plant growth.
(i) Potassium in fertilizers may be in the form of potassium nitrate Describe how a sample of a fertilizer may be tested to find out if it contained nitrate ions. (ii) Calculate the mass of nitrogen present if a 25kg bag contained pure ammonium phosphate, (NH4)2 HPO4. (N = 14.0, H=1.0, P = 31.0, O = 16.0 (b) The table below shows the solubility of ammonium phosphate in water at different temperatures.
(i) On the grid provided, draw the solubility curve of ammonium phosphate (Temperature on x – axis)
(ii) Using the graph, determine the solubility of ammonium phosphate at 25°C (iii) 100g of a saturated solution of ammonium phosphate was prepared at 25°C I what is meant by a saturated solution? II Calculate the mass of ammonium phosphate which was used to prepare the saturated solution (c) The graph below shows how the PH value of soil in a farm changed over a period of time
(i) Describe how the pH of the soil can be determined
(ii) State one factor that may have been responsible for the change in the soil pH in the time interval AB
(a) The diagram below represents part of the structure of a sodium chloride crystal.
The position of one of the sodium ions in the crystal is shown as (i) On the diagram, mark the position of the other three sodium ions (ii) The melting and boiling points of sodium chloride are 801°C and 1413°C respectively. Explain why sodium chloride does not conduct electricity at 25°C, but does so at temperatures between 801° C and 1413°C (b) Give a reason why ammonia gas is highly soluble in water (c) The structure of an ammonia ion is shown below:
Name the type of bond represented in the diagram by N → H
(d) Carbon exists in different crystalline forms. Some of these forms were recently discovered in soot and are called fullerenes (i) What name is given to different crystalline forms of the same element? (ii) Fullerenes dissolve in methylbenzene while the other forms of carbon do not. Given that soot is a mixture of fullerenes and other solid forms of carbon, describe how crystals of fullerenes can be obtained from soot. (iii) The relative molecular mass of one of the fullerenes is 720. What is the molecular formula of this fullerene? (C=12.0)
(a) Methanol is manufactured from carbon (IV) oxide and hydrogen gas according to the equation:
The reaction is carried out in the presence of a chromium catalyst at 700K and 30kPa. Under these conditions, equilibrium is reacted when 2% of the carbon (IV) oxide is converted to methanol
(i) How does the rate of the forward reaction compare with that of the reverse reaction when 2% of the carbon (IV) oxide is converted to methanol? (ii) Explain how each of the following would affect the yield of methanol: I Reduction II Using a more efficient catalyst (iii) If the reaction is carried out at 500K and 30kPa, the percentage of carbon (IV) oxide converted to methanol is higher than 2% I what is the sign of ΔH for the reaction? Give a reason II Explain why in practice the reaction is carried out at 700K but NOT at 500K (b) Hydrogen peroxide decomposes according to the following equation : 2H2O2(aq) →2H2O(l) + O2 (g) In an experiment, the rate of decomposition of hydrogen peroxide was found to be 6.0 x 10-8 mol dm-3 S-1. (i) Calculate the number of moles per dm3 of hydrogen peroxide that had decomposed within the first 2 minutes (ii) In another experiment, the rate of decomposition was found to be 1.8 x 10-7 mol dm-3S-1. The difference in two rates could have been caused by addition of a catalyst. State, giving reasons, one other factor that may have caused the difference in two rates of decomposition
The flow chart below shows a sequence of chemical reactions starting with copper study it and answer the questions that follow.
(a) In step 1, excess 3M nitric acid was added to 0.5g of copper powder
(i) State two observations which were made when the reactions was in progress (ii) Explain why dilute hydrochloric acid cannot be used in step 1 (iii) I Write the equation for the reaction that took place in step 1 II Calculate the volume of 3M nitric that was needed to react completely with 0.5g of copper powder. (Cu = 63.5) (b) Give the names of the types of reactions that took place in steps 4 and 5 Step 4 Step 5 (c) Apart from the good conductivity of electricity, state two other properties that make it possible for copper to be extensively used in the electrical industry.
(a) Give the systematic names of the following compounds
(b) State the observations made when Propan – 1- ol reacts with:
(i) Acidified potassium dichromate (VI) Solution (ii) Sodium metal (c) Ethanol obtained from glucose can be converted to ethane as shown below
Name and describe the process that take place in steps I and IIStep I Step II
(d) Compounds A and B have the same molecular formula C3H6O2. Compound A liberates carbon (IV) oxide on addition of aqueous sodium carbonate while compound B does not. Compound B has a sweet smell. Draw the possible structures of: (i) Compound A (ii) Compound B (e) Give two reasons why the disposal of polymers such as polychloroethane by burning pollutes the environment.
(a) State two factors that should be considered when choosing fuel for cooking
(b) The diagram below represents a set – up that was used to determine the molar heat of combustion of ethanol
During the experiment, the data given below was recorded
Calculate the:
(i) Heat evolved during the experiment (density of water = 1g/cm3 Specific heat capacity of water = 4.2 Jg-1K-1 (ii) Molar heat of combustion of ethanol (C = 12.0, O = 16.0, H=1.0) (c) Write the equation for the complete combustion of ethanol (d) The value of the molar heat of combustion of ethanol obtained in (b) (ii) above is lower than the theoretical value. State two sources of error in the experiment.
The table below shows the volumes of nitrogen dioxide gas produced when different volume of 1M nitric acid were each reacted with 2.07 g of lead at room temperature.
a) Give a reason why nitric acid is not used to prepare hydrogen gas. b) Explain how the rate of the reaction between lead and nitric acid would be affected if the temperature of the reaction mixture was raised. c) On the grid provided below, plot a graph of the volume of the gas produced (Vertical axis) against volume of acid.
d) Using the graph, determine the volume of
:i) Nitrogen dioxide produced when 30cm3 of 1 M nitric acid were reacted with 2.07 g of lead ii) 1M nitric acid which would react completely with 2.07g of lead. e) Using the answer in d(i) above, determine: i) The volume of 1M nitric acid that would react completely with one mole of lead (Pb=207) ii) The volume of nitrogen dioxide gas produced when one mole of lead reacts with excess 1 M nitric room temperature. f) Calculate the number of moles of: i) 1M nitric acid that reacted with one mole of lead ii) nitrogen dioxide produced when one mole of lead were reacted with excess nitric acid. (Molar gas volume of 2400cm3) g) Using the answers obtained in f (i) and (ii) above, write the equation for the reaction between lead and nitric acid given that one mole of lead nitrate and two moles of water were also produced.
The extraction of iron from its ores takes place in the blast furnace. Study it and answer the questions that follow.
a) Name
(i) One of the substances in the slag (ii) Another iron ore material used in the blast furnance. (iii) One gas which is recycled. b) Describe the process which leacd to the formation of iron in the blast furnace c) State the purpose of limestone in the blast furnace. d) Give a reason why the melting point of the iron obtained from the blast furnace is 12000 C while tat of pure iron is 15350C (e) State two uses of steel
a) What name is given to a compound that contains carbon and hydrogen only?
b) Hexane is a compound containing carbon and hydrogen. (i) What method is used to obtain hexane from crude oil? (ii) State one use of hexane c) Study the flow chart below and answer the questions that follow.
(i) Identify reagent L.
(ii) Name the catalyst used in step 5. (iii) Draw the structural formula of gas J. (iv) What name is given to the process that takes place in step 5? d) (i) write the equation for the reaction between aqueous sodium hydroxide and aqueous ethanoic acid. (ii) Explain why the reaction between 1g of sodium carbonate and 2M hydrochloric acid is faster than the reaction between 1g of sodium carbonate and 2M ethanoic acid. |
Chemistry Topics
All
Archives
December 2024
|
We Would Love to Have You Visit Soon! |
Hours24 HR Service
|
Telephone0728 450425
|
|
8-4-4 materialsLevels
Subjects
|
cbc materialsE.C.D.E
Lower Primary
Upper Primary
Lower Secondary
Upper Secondary
|
teacher support
Other Blogs
|