CHEMISTRY PAPER 1 - KCSE 2019 STAREHE PRE MOCK EXAMINATION (WITH MARKING SCHEME)

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  1.  
    1. Define the term isotopes     [1mk]
    2. The table below shows the isotopic composition of element Q

      Isotope

      relative

       CHEM21

      90.92

       CHEM20

      X

       CHEM22

      0.26


      1. In CHEM20, what does 21 represent?      [1mk]
      2. Determine value of X  [1mk]
      3. Hence calculate R.A.M of Q     [2mks]
  1.  
    1. State Grahams law of diffusion                                                                                  [1mks]
    2. 400cm3 of nitrogen gas diffuse through a porous plug in 120 seconds. How long would it take 360cm3of oxygen gas to diffuse under the same conditions?
      {N=14, O=16}    [3mks]
  1. Acid rain is formed when rain falls through air polluted with carbon (IV) oxide and Sulphur(IV)oxide. Identify two acids possibly present in such an acid rain    [2mks]
  1. Ca2+ is one of the cations present in hard water that makes water to be hard
    1. Identify another cation responsible for water hardness                                               [1mk]
    2. One method of removing permanent hardness in water is by use of ion exchanger
      1. State two other methods that can be used                                                         [2mks]
      2. After continuous use the ion exchanger column gradually looses the water hardness. How can its ability be recovered?     [1mk]
    3. State one disadvantage of water hardness                                                                   [1mk]
  1. The empirical formulae of a compound is given as C2H4O. Given that its R.M.M is 88, find its molecular formulae   {C=12, H=1, O=16}  [2mks]
  2. 29 grams of a saturated solution of salt M at 350C yield 8.5 grams of solid when evaporated to dryness. Determine the solubility of the salt at 350C  [2mks]
  3. In an experiment, copper metal was heated in the air to form a black solid T. dilute Sulphuric {VI} acid was then added to solid T resulting to formation of solution W, after which Ammonia was then added to solution W drop wise till excess
    1. Identify solid T                                                                                                                  [1mk]
    2. Write a chemical equation for the reaction leading to formation of solution W         [1mk]
    3. State the observations made when the am monia solution was added to solution W drop wise till excess            [2mks]
  1. What name is given to each of the following?
    1. Ability of a metal to be beaten/ hammered to a sheet      [1mk]
    2. Force of attraction that holds two molecules together        [1mk]
  1. Draw the structures and name two hydrocarbons with molecular formulae C4H10 [4mks]
  1. 800cm3 of a gas exert a pressure of 520mmHg at 750C .What pressure would 700cm3 of the same gas exert at 1000C?   [2mks]
  2. Aluminium is one of the metals that is commonly used in making cooking utensils. State two properties of aluminium that makes it suitable for this use [2mks]
  3. Given the following bond energies in KJmole-1
    Bond                                                 Energy [KJmole-1]
    C –C                                                              348
    C – H                                                              414
    Cl -Cl                                                             243
    C -Cl                                                              432                                                      
    H – Cl                                                             340
    1. Determine the enthalpy charge in the following reaction
      C2H6 [g] + Cl2[g]  → CH3CH2Cl[g] + HCl[g]                            [3mks]
    2. state whether the reaction was exothermic or endothermic    [1mk]
  1. The grid below shows a section of the periodic table
    CHEM13GRID
    1. Which letter represents the least reactive element? Explain your answer                                [2mks]
    2. Which letter represents the most electropositive element?                                                         [1mk]
    3. What name is given to the family into which element X belongs to?                                         [1mk]
    4. How does the electrical conductivity of element Y and Z compare? Explain                           [2mks]
  1. Describe how you can prepare a dry sample of lead (II) carbonate starting with lead (II) nitrate crystals [3mks]
  1. Explain why the relative molecular mass of NO2 is sometimes 92 instead of 46                             [2mks]
  2. Using dots and crosses, show bonding in the following                                                                  [3mks]
    1. H2O
    2. H2O+
  1. The diagram below shows part of a set-up used to prepare a solution of hydrogen chloride gas in water
    CHEM17FUNNEL
    1. What property of hydrogen chloride gas makes it necessary to prepare its solution in water as shown on the diagram      [1mk]
    2. Give two reagents that can be used to prepare hydrogen chloride                                   [2mks
    3. State and explain the effect on red litmus paper when dropped in the resulting solution  [2mks]
  1. When 3.1g of Copper {II} Carbonate were heated in a crucible until no further change in mass, solid L and gas M were formed
    1. Identify solid L and gas M                                                                                         [2mks]
    2. Write a chemical equation for the reaction that occurred                                           [1mk]
    3. Given Cu=64, C=12,O=16, calculate the mass of the solid L that was formed          [2mks]
  1. In terms of structure and bonding explain why silicon (IV) oxide has a higher melting point than phosphorous (IV) oxide      [2mks]
  2. Briefly describe two experiments that can be used to distinguish nitrogen (I) oxide and Nitrogen (II) oxide [4mks]
  3. Manganese (IV) oxide is a common reagent used in the preparation of chloride gas using concentrated hydrochloric acid and preparation of oxygen gas using hydrogen peroxide
    1. State the role of manganese(IV) oxide in the preparation of;
      1. Chlorine gas        [1mk]
      2. Oxygen gas         [1mk]
    2. State two physical properties of chlorine gas  [2mks]
  1. Give two reasons why air is considered a mixture and not a compound                                   [2mks]
  2. Sulphur has two allotropic forms
    1. Identify the two allotropic forms                                                                                    [2mks]
    2. Which of the allotropes is most stable at temperatures below 960C                                 [1mk]
  1. Rusting is a common chemical process that occurs on the surface of materials made of iron
    1. What is the chemical name of rust                                                                                   [1mk]
    2. Identify two conditions that accelerate the rusting process                                             [2mks]


MARKING SCHEME

  1.  
    1. Isotopes are atoms of the same element with same atomic number but different mass number.   √1
    2.  
      1. Mass number    √1
      2.  
         CHEM1DEC              
  1.  
    1. Grahams law states that under the same conditions of temperature and pressure, the rate of diffusionof a gas is inversely proportional to the squireroot of its density.   √1
    2.  
      CHEM2DEC
  1. Carbonic acid   √1
    Sulphuric (IV) acid  √1
  1.  
    1. Mg2+   √1
    2.  
      1. distillation√1
        Precipitation by sodium carbonate    √1
      2. by flashing it with brine/ concentrated sodium chloride√1
    3. waste soap    √1
      Stains white clothes.
      (Any one correct)
  1. Molecular mass=( E.F)n
    CHEM5DEC
  1. Mass of the solvent. 29.0- 8.5=  20.5
    CHEM6DEC
  1.  
    1. copper (ii) oxide/ CuO√1
    2. CuO(s)  +  H2SO4(aq) → CuSO4(aq)  + H2O(l)   √1
    3. pale blue ppt formed, which dissolves√ in excess ammonia solution to form deep blue solution.√
  1.  
    1. malleable √1
    2. vandarwaals forces    √1
  1.  
    CHEM9DEC
  1.  
    CHEM10DEC
  1. Alluminium is a good conductor of electricity  √1
    It is not easlycorroded  √1
  1.  
    1.  
      CHEM12DEC
    2. Exothermic √1
  1.  
    1. X, √1 has maximum number of electrons√1 in the outer most energy level hence has least tendency to loose or gain electrons.
    2. B  √1
    3. Noble gases√1
    4. Z has more electrical conductivity because it has more delocalized electrons.   √1
  1. Add lead (ii) nitrate to a beaker with distilled water and stir. √
    filter√  to obtain a solution of lead (II) nitrate.
    Add a solution of sodium carbonate √ (any soluble carbonate) to lead (ii) nitrate solution.
    Filter √the mixture to obtain the insoluble lead (ii) carbonate as the residue
    Rinse the residue with distilled water √
    Dry it between filter papers√
  1. NO2 forms a dimer which is N2O4√1 hence the mass number doubles   √1
  1.  
    1.  
      CHEM16DEC 
    2.  
      CHEM16BDEC
  1.  
    1. its highly soluble in water   √1
    2. concentratedsulphuric(vi) acid and rock salt/ sodium chloride
    3. it remains red because the solution is acidic.
  1.  
    1. Solid L- nCopper (ii) oxide   √1
      Gas M- carbon (iv) oxide√1
    2. CuCO3(s) →   CuO     +CO2(g)
    3. CuCO3(s) →CuO     +CO2(g)
      mm-124     82            44
      given mass 3.1
      CHEM18DEC
  1. Silicon (iv) oxide√has a giant atomic√ structure with strong covalent bond while phosphorous (v) oxide has molecular √structure with weak van der waals forces of attraction.   √
  1. Lower a glowing splint into a sample of each in gas jar. √1 nitrogen (i) oxide relights the glowing splint while nitrogen (ii) oxides does not.   √1
    Pass air through a sample of each in the gas jar nitrogen (ii) oxide is oxidized to brown nitrogen (iv) oxide while nitrogen (i) oxide does not react with air.
  1.  
    1.  
      1. acts as an oxidizing agent   √1
      2. acts as a catalyst   √1
    2. soluble in water  √1
      Green yellow gas √1
      Its denser than air   √1
    3. Any two correct
  1. Components of air are not chemically combined√1
    Components of air can be separated by physical means√1
    Each of the components of air retains its physical and chemical properties√1
    Any two correct
  1.  
    1. Rhombic sulphur√1
      Monoclinic sulphur√1
    2. Rhombic sulphur√1
  1.  
    1. hydrated iron (iii) oxide    √1
    2. salty condition    √1
      Acidic condition  √1

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