MOKASA Joint Evaluation Examination Chemistry Paper 1 2016- Pre MOCK with answers

1. It is always advisable to scoop chemical substances using a clean spatula. ( ½ mark)

    To prevent contamination of the chemicals.

2. Flammable substances should always be kept away from flames in the laboratory. ( ½ mark)

   To prevent fire accidents.

 Ammonia solution

Al³⁺ - A white precipitate would be formed which is insoluble in excess ammonia solution.

Zn²⁺ - A white precipitate would be formed which is insoluble in excess ammonia solution.

1. Water is added to the equilibrium mixture. (1 ½ marks)

    Increasing the concentration of water would shift the equilibrium to the left.

2. Hydrogen chloride is bubbled into the equilibrium mixture. (1 ½ marks)

    HCl would react with the H2S thereby reducing its concentration.  The equilibrium would shift to the right.

1. Draw an energy cycle diagram to show the enthalpy of formation of ethane. (1 ½ marks)
2. Calculate the enthalpy of formation of ethane. (1 ½ marks)

    ΔH_f  = ΔH₁ + ΔH₂ - ΔH₃
             = (2 x - 394) + (3 x -286) - 1560
           = -788 + -856 - -1560
           = -1646 + 1560
           = -86 kJ/mole

The acid must be concentrated and hot 
Cu_(s) + H₂SO_4(l) --------> CuSO_4(aq) + SO_2(g) + H₂O_(l)

1. Write the structural formula of the monomer of Perspex. (1 mark)

    

2. State the type of polymerization involved in the formation of perspex. (1 mark)

    Addition polymerization

Zn_(s) + H₂SO_4(aq) ---------> ZnSO_4(aq) + H_2(g)
Zn_(s) + 2H₂SO_4(l) ---------> ZnSO_4(aq) + SO_2(g) + 2H₂O_(l)

1. Identity solid X. (1 mark)

    Hydrated iron (III) oxide

2. Write an ionic equation for the reaction between P and copper (II) sulphide solution. (1 mark)

    H₂S_(g)  +  Cu²⁺_(aq)  --------------->  CuS_(s)   +  2H⁺_(aq)

3. State the observation made when gas P is bubbled through iron (III) chloride solution. (1 mark)

    The yellow iron (III) chloride solution turns green.

1. Give the actual names of particles X and Y. (1 mark)

    X -  Alpha particles

    Y   Beta particles

2. Give the name of a radiation whose emission does not change the mass number or the atomic number of a radioisotope. (1 mark)

    Gamma radiatons

 P – when used with hard water it does not form scum.

1. Obtain an equation of the cell reaction. (1 mark)

    Mg_(s)  +  Zn²⁺_(aq)  ------------>    Mg²⁺_(aq)  +  Zn_(s)

2. Calculate the value E^ϑ for the cell. (1 mark)

    E.m.f = E^ϑ reduced - E^ϑ oxidised
            = -0.76 + 2.37
            = +1.61V

3. Give the oxidizing species. (1 mark)

    Zn²⁺ ion

1. Aluminium chloride. (1 ½ marks)
2. Sulphuric (IV) oxide. (1 ½ marks)
   
   

1. Write the electron arrangement of: (1 mark)
   1. ion of S

       2.8

   2. atom of T

       2.8.4

2. Explain why the melting point of T is higher than that of U. (2 marks)

   Atoms are covalently bonded together to form a giant atomic structure.  Atoms of U are bonded covalently to form molecules.  The molecules are then hold together by weak Van der waals to form a simple molecule structure.

1. Name substance X. (1 mark)

    Hydrogen

2. What is the purpose of the glass beads? (1 mark)

    They increase the surface area over which the gas dissolves in water.

3. Give one use of hydrochloric acid. (1 mark)
   

   -Treatment of water at the water works
   -Sewage treatment
   -Manufacture of dyes, drugs etc
   -To clean metal surfaces to remove rust

1. iron reacts with steam. (1 mark)

    3Fe_(s)  +  4H₂O_(g)  --------->     Fe₃O_4(s)   +  4H_2(g)

2. Give one industrial use of the gas produced in the reactions in (i) and (ii) above. (1 mark)

   -Industrial manufacture of hydrochloric acid
   -Industrial manufacture of Ammonia
   -Used in weather balloons

1. When magnesium metal is burnt in air, it reacts with both oxygen and nitrogen gases giving a white ash. Write two equations for the reactions that take place. (2 marks)

   2Mg_(s) + O_2(g) -------> 2MgO_(s)
   3Mg_(s) + N_2(g) --------> Mg₃N_2(s)

2. Give the total number of atoms present in the gas produced when water is added to magnesium nitrate. (1 mark)

    Four

1. What is the relationship between the volume and the pressure of the gas? (1 mark)

    At constant temperature, the volume of a fixed mass of gas is inversely proportional to pressure or  V  α  ¹/_p   ,  V  = ^K/_P

2. 60 cm³ of oxygen gas diffused through a porous partition in 50 seconds. How long would it take 60 cm³ of sulphur (IV) oxide gas to diffuse through the same partition under the same conditions? (S = 32.), O = 16.0) (3 marks)

    

 The red litmus paper is bleached.  This is because chlorine gas has bleaching property.

1. When extinguishing a fire caused by burning kerosene, carbon (IV) oxide is preferred to water. Explain. (2 marks)

    Kerosene floats on water therefore it continues to burn.  Carbon (IV) oxide cuts off the supply of oxygen.

2. Write the formula of the oxide of carbon which is ‘silent killer’. (1 mark)

    CO

 The molecules of chlorine are smaller compared to those of iodine; thus the strength of the intermolecules forces of attraction in iodine are much stronger than in chlorine.

A proton is positively charged whereas an electron is negatively charged.
The mass of a proton is/atomic mass units whereas that of an electron is ¹/₁₈₄₀ a.m.u

 Electron affinity

 Add water to a small sample of the fertilizer in a test tube and shake well.  Filter to obtain a solution.  To the solution add some freshly prepared ion (II) sulphate solution and shake well.  With a test tube in a slanting position, add concentrated sulphuric (VI) acid to the mixture carefully along one side of the tube.  A brown ring between two layers indicates the presence of nitrate ions.

1. Lead (II) nitrate (1 mark)

    2Pb(NO₃)_{2 (s)} 2PbO_(s)   +  4NO_2(s)    +  O_2(g)

2. Silver nitrate (1 mark)

    2Ag NO_3(s)   --------->     2Ag_(s)  +2NO_2(g)   +   O_2(g)

 An oxide that behaves as an acid or a base in chemical reactions.

 Heat the zinc carbonate  solid in a test tube to obtain zinc oxide.  To a certain volume of dilute nitric (V) acid the zinc oxide a little at a time while stirring till in excess.  Filter the unreacted zinc oxise.  To the filtrate add aqueous

1. Name Y, X and T (1 ½ marks)

    Y Chlorine gas

    X Hydrogen gas

    T Butyl hydrogen sulphate

2. Give the name of the following organic compounds. ( ½ mark)
   
   

    Ethanoic acid

   

    Ethylpropanoate

   

    Sodium ethanoate