CHEMISTRY PAPER 1 - KCSE 2019 NYANDARUA PRE MOCK EXAMINATION

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  1. The diagram below shows a Bunsen burner which is used as a source of heat in the laboratory.
    CHEM1JET
    1. Name the parts labeled: A and B                                                                      (2 marks)
    2. Explain how the hotness of a non-luminous flame can be increased.    (1 mark)
  2. In an experiment to separate a mixture of two immiscible liquids A and B, a form four student set the apparatus as shown below.
    CHEM2JET
    1. Name the above apparatus. ( 1 mark)
    2. Which liquid is denser? (1 mark)
    3. Name one other method that can be used to separate the above mixture. (1 mark)
  3. The following chromatogram shows the results obtained after separating substances P and T.
    CHEM3JET
    1. Name lines; A and B (1 mark)       
    2. Name the possible solvent that can be used in the above process. (1 mark)
    3. Which of the two substances is pure? (1 mark)
  4. A form four student arranged the apparatus as shown below with the aim of collecting dry hydrogen gas
    CHEM4JET
    Identify with reasons two mistakes in the above set-up.                                (3 marks)
  1. The table below shows elements and their atomic numbers. The letters do not represent the actual symbols of the elements.

    Element

    A

    B

    C

    D

    E

    F

    G

    Atomic number

    11

    10

    20

    13

    14

    6

    8


    1. From the given letters, select two elements with the same chemical properties.       (1 mark)
    2. Write the formula of the compound formed when element E reacts with element G.      (1 mark)
    3. Identify the most stable element and give a reason for your answer. (1 mark)
  2. When magnesium burns in air, it forms two products. When one of the products dissolves in water, a colorless gas that turns red litmus paper blue is formed.
    1. Name the product that dissolves in water to produce a colorless gas. (1 mark)
    2. Write an equation for the formation of the colorless gas. (1 mark)
    3. State any one use of the colorless gas. (1 mark)
  3. A student was given a mixture ammonium chloride, copper (II) oxide and sodium chloride. Describe how the student would separate the mixture.
  4. When small amount of carbon (IV) oxide is passed through lime water, a white precipitate is formed. When excess carbon (IV) oxide is bubbled through, the white precipitate dissolves to form a colorless solution.
    1. Name the white precipitate. (1 mark)
    2. Explain using chemical equations why the white precipitate dissolves in excess of carbon(IV) oxide. (1 mark)
    3. What will happen of the above colorless solution is boiled. (1 mark)
  5. Write equations to show the effect of heat on each of the following.
    1. Sodium hydrogen carbonate.    (1 mark)
    2. Silver nitrate             (1 mark)
    3. Sodium nitrate        ( 1 mark )
  6.  
    1. State the Graham’s law of diffusion.                                                             (1 mark)
    2. A sample of unknown gas Z was shown by analysis to contain sulphur and oxygen. The gas requires 28.3 seconds to diffuse through an aperture into a vacuum. An identical amount of oxygen gas passes through the same aperture in 20 seconds. Determine the molar mass of gas Z. (O=16, S=32).                  (2 marks)
  1. When a hydrated sample of CaSO4 .XH2O was heated until there all the water was lost, the following data was obtained.
    Mass of the crucible = 30.296g
    Mass of crucible + hydrated salt = 33.111g
    Mass of crucible + anhydrous salt = 32.781g

    Determine the empirical formula of the hydrated salt. (Ca=40, S=32, O=16, H=1)       (3 marks)
  1. The empirical formula of a compound is C2H5. When 11.6g of the compound was allowed to evaporate; it occupied 4.8 dm3 at room temperature and pressure. What is its molecular formula? (MGV = 24dm3)                                                 (3marks)
  2. The diagram below shows an industrial process that is used in extraction of sulphur.
    CHEM13JET
    1. What is the name given to the above industrial process? (1 mark)
    2. Identify substance X. (1mark)
    3. What is the role of super-heated water? ( 1mark)
  3.  
    1. Give the systematic names for the following compounds.
      1. CH3CH2CHCH2                                     ( mark)
      2. CH3CH2CH3                         ( mark)
    2. Describe one chemical process that can be used to distinguish between the substances named in (a) above. (2 marks)
  4. The set-up below was used to prepare Nitric(V) acid in the laboratory.
    CHEM15JET
    1. Name liquid T. (1 mark)
    2. Write an equation for th reaction taking place in the flask. (1 mark)
    3. State the reason why nitric(V) acid collected is brown in colour and explain how the brown colour can be removed. (1 mark)
  5. Ammonia gas was passed into water as shown below. 
    CHEM16JET
    1. What is the use of the inverted funnel?           (1 mark)
    2. State and explain the observation made when a red litmus paper is dipped into the above solution.  (1 mark)
  1. Study the flow chart below showing the reaction involved in the preparation of sulphuric (IV) acid and answer the questions that follow.
    CHEM17JET
    1. Name the reagents.
      L_______________________ (1/2mk)  
      M_______________________ (1/2mk)
    2. Write the equation for the reaction between reagent M   and   H2S2O7                         (1mk)
    3. State one industrial use of sulphuric(VI) acid. (1 mark)                     
  1.  
    1. What is meant by the term strong acid? (1 mark)
    2. In an experiment, 40cm3 of 0.5M sulphuric (VI) acid was reacted with excess sodium carbonate and the volume of cabon (IV) oxide produced recorded with time. In another experiment, 40cm3 of 0.5M ethanioc acid was reacted with excess sodium carbonate and the volume of carbon (IV) oxide produced recorded with time. On the grid below, sketch and label the curves if the volumes of carbon (IV) oxide were plotted against time on the same axis.     (2 marks)
  1. Hydrogen chloride gas is soluble in both water and methylbenzene. State and explain the observation made when a small piece of magnesium ribbon is placed in each of the solutions.
    1. Solution of HCl(g) in methylbenzene             (1 marks)
    2. Solution of HCl(g) in water.                         (1 marks)
  2. The scheme below shows a reaction sequence starting with solid N. study it and answer the questions that follows. 
    CHEM20JET
    1. Name the cation present in solid N. (1 mark)
    2. Write the formula of the complex ion in the colorless solution Q. (1 mark)
    3. Write an ionic equation for the reaction in step 2. (1 mark)
  3. Reagent bottles labelled H2SO4 solution, K2CO3 solution and NaCl solution had labels accidentally removed. A packet of blue litmus paper is lying near a long with a rack of test-tubes, without using any other material explain how you would go about labeling the bottles correctly.                                                                         (3marks)
  4. Some bond energies are given below;

    Bond

    Energy (kJmol-1)

    C-C

    348

    C-H

    414

    Cl-Cl

    243

    C-Cl

    432

    H-Cl

    340


    Calculate the energy change for the reaction below.                                       (3 marks)
    C2H6(g) + Cl2(g) →CH3CH2Cl(g) + HCl(g)      
  5.  
    1. What is fractional crystallization? (1 mark)
    2. The solubility of copper (II) sulphate is 55g/100g of water at 75oC and 19g/100g of water at 15oC. What mass of crystals would be deposited, if 150g of a saturated solution is cooled from 75oC to 15oC.                                                                        (2 marks)
  1. Study the equation below and answer the question that follows.
    NH3(g) + H20(l) →NH4+(aq)   + OH-(aq)
    Identify two species that acts as an acid. Give a reason for your answer. (3 marks)
  1. Using well labeled diagrams, explain how water hardness can be removed by ion exchange method. (3 marks)
  2. Substances X and Y consists of molecules X2 and Y2 When the two elements react, they form a molecule of XY. The X-X bonds are as strong as Y-Y bonds. But the X-Y bond is stronger than both X-X and Y-Y bonds.
    X2(g) + Y2(g) →2 XY(g)
    1. Is the above reaction exothermic or endothermic? Give a reason for your answer.      (2 marks)
    2. Draw an energy level diagram for the reaction in (a) above. (1 mark)
  3. The diagram below shows acidic and basic oxides fit in a general family of oxides.
    CHEM27JET
    1. State the name given to the type of oxides that would be placed in the shaded region.    (1 mark)
    2. Name two oxides that could be placed on the shaded region. (2 marks)


MARKING SCHEME

  1.  
    1. A- Chimney P¹
      B- Air hole P¹
    2. By opening the air hole completely to allow more air into the chimney for the laboratory gas to burn completely. P¹
  2.  
    1. Separating funnel P¹
    2. Liquid B P¹
    3. Decantation P¹
  3.  
    1. A- Solvent front P½
      B- Base-line P½
    2. Propanone, acetone, P¹
      TP½- Separates into one component only P½
  4. –The gas is being collected through downwards deliveryP¹ yet it is less denser than airP½
    -The delivery tube removing the gas from flask B is dipped into the concentrated H2SO4P¹, hence the gas cannot collectedP½.
  1.  
    1. E & F P¹
    2. EG2
    3. B P½- Has a filled outermost energy level. P½
  2.  
    1. Magnesium nitride P¹
    2. Mg3N2(s) + 3H20(l) →3Mg(OH)2(aq) + 2NH3(g)
    3. Manufacture of nitrogenous fertilizer, Manufacture of nitric (V) acid, As a refrigerant e.g. in large scale refrigerating plant such as ships and warehouses, Softening water, Removal of greasy stain, Manufacture of hydrazine that is used as rocket fuel. P¹
  3. –Heat the mixture to sublime P¹ ammonium chloride leaving behind a mixture of copper(II) oxide and sodium chloride
    -Add water to the remaining mixture, stir to dissolve sodium chloride P¹
    -filter to obtain copper(II) oxide as the residue and sodium chloride solution as the filtrate P¹
    -Heat the filtrate to evaporate water leaving behind sodium chloride. P¹
  1. Calcium carbonate P¹ 
    1. CaCO3 reacts with excess carbon(IV) oxide to form soluble calciumhydrogen carbonate hence the precipitate dissolves. P½
    2. CaCO3(s) + CO2(g) + H2O(l) →Ca(HCO3)2(aq)
    3. A white precipitate of CaCO3 will be formed. P¹ 
  2.  
    1. 2NaHCO3(s)→ Na2CO3(s) + H2O(l) + CO2(g)  
    2. 2AgNO3(s) → 2Ag(s) + 2NO2(g) + O2(g)
    3. 2NaNO3(s) 2NaNO2(s) + O2(g)
  3.  
    1. Under the same conditions of temperature and pressure, the rate of diffusion of a gas is inversely proportional the square root of its density. P¹
    2.  
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  1. Mass water: 33.111 - 32.781 = 0.33gP½
    Mass of CaSO4: 32.781 – 30.296 = 2.485gP½
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  1.  
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  1.  
    1. Frasch process P¹
    2. Hot compressed air P¹
    3. To melt sulphur P¹
  2.  
    1.  
      1. But-1-ene P½
      2. Propane P½
    2. Use of acidified potassium manganite (VI) solution or bromine water P¹whereby but-1-ene decolorizes these solutions while propane does not. P¹
  3.  
    1. Concentrated sulphuric(VI) acid P¹
    2. H2SO4(l) + NaNO3(s) → NaHSO4(s) + HNO3(l)
    3. Contains dissolved NO2 P½- The yellow colour can be removed by bubbling air through the acid. P½
  4.  
    1. To prevent suck back by increasing the surface area over which the gas dissolves in water. P¹
    2. Turns from red to blueP¹- Ammonia dissolves in water forming an alkaline solution. P¹
  5.  
    1. L- Water P½,      
      M- Concentrated sulphuric(VI) acid P½
    2. H2S2O7(l) + H2O(l)→ H2SO4(l)  
    3. Manufacture of fertilizers e.g. ammonium sulphate, Processing of metal ores, Manufacture of detergents, Manufacture of plastics, Manufacture of dyes and paints and explosives, In car batteries as an electrolyte, In petroleum refining, Production of synthetic fibres. P¹
  6.  
    1. An acid that undergoes complete dissociation in its aqueous state.
    2.  
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  1.  
    1. No effervescence:- P½ Methylbenzene is a non-polarP½ solvent hence HCl does not dissociateP½ thus the solution lacks H+
    2. Effervescence occursP½:- Water is a polarP½ solvent. HCl dissociates P½releasing H+ thus the solution shows acidic properties.
  2.  
    1. Zinc ions P¹
    2. [Zn(NH4)]2+       P¹
    3. Zn2+(aq) + 2OH-(aq) →Zn(OH)2(s)
  3. Dip the blue litmus paper in each ü ½ solution. H2SO4 turns it red ü ½ while K2CO3 and NaCl have no effect ü ½ transfer the two unknown solutions to a test tube. Add H2SO4 to each solutions ü ½ solution with K2CO3 give vigorous effervescence ü ½ while solution of NaCl give no observable ü ½
  1. Bonds broken Bonds formed
    1(C-H) 1× 414 = 414kJ                   1(C-Cl) 1×432= 432kJ
    1(Cl-Cl) 1× 243 = 243kJ                    1(H-Cl) 1× 340= 340kJ
    Total= + 657kJ P¹                            Total= -772kJ P¹
    Net enthaply change 657-772= -115kJMol-1 P¹
  1.  
    1. This refers to separation of different salts by making use of their differences in solubility in the same solvent. P¹
    2. 150g of the saturated solution contains 50g of the salt in 100g of water.
      Solubility at 15oc is 19g/100g of waterP¹                                              
      Mass of the salt to crystallized   50g-19g = 31g P¹
  1. H2O in the forward reactionP¹ and NH4+ in backwards reactionP¹: They are donating H+P¹
  2. Hard water containing Ca2+ and Mg2+ is passed through a column packed with a sodium complex (Na2X). Ca2+ and Mg2+ precipitates as CaX and MgX which remains in the columnP¹.
    Na2X(s) + Ca2+(aq) →CaX(s) + 2Na+(aq)
    Na2X(s) + Mg2+(aq)→MgX(s) + 2Na+(aq)                                   P¹
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  1.  
    1. Exothermic P¹:- More energy will be released when X-Y bonds are formed than the energy required to break both X-X and Y-Y bond OR X-Y is stronger than both X-X and Y-Y bonds. P¹
    2.  
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  1.  
    1. Amphoteric oxidesP¹
    2. Zinc oxide, aluminum oxide, lead(II)oxideP¹

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