Chemistry Paper 2 Questions and Answers - Form 4 Term 3 Opener Exams 2023

• Answer all the questions
• Candidates should answer the questions in English.

1. The table below represents some elements.  Use it to answer the questions that follow.  The letters do not represent the actual symbols of the element. 
   

   Element	Atomic Number	Melting point °C
   Q  R  S  T  U	11  13  14  17  19	97.8  660  1410  −101  63.7

   1. Write the electron arrangement for the ions formed by elements.   
      1. R          ( 1 mk)
      2. T          ( 1 mk)
   2. Select an element which is ;                             
      1. The most reactive metal                                               ( ½ mk)
      2. A semi-conductor of electricity.                                 ( ½ mk)
   3. Compare the atomic radius of Q and R.  Explain     ( 2mk)
   4. Use dots (.) and crosses (x) to represent electrons, show the bonding formed between S and T.  (1mk)
   5. Explain why the melting point of S is higher than that of Q  (2mks)
   6.  
      1. Write an equation for the reaction between Q and water.  (1mk)
      2. Calculate the mass of the solid formed when excess R reacts with 960cm³ of oxygen gas. (MGV= 24dm³, O=16, Al=23)        (2mk)
2.  
   1. Use the information below to answer questions that follows
      Ca_(s)   + ½O_2(g)  →  CaO_(s)   ∆H = −635kJ/mole
      C_(s)   +  O_2(g)   →    CO_2(g)    ∆H = −394kJ/mole
      Ca_(s)   +  C_(s)   + ³/₂O_2(g)  →   CaCO_3(s)  ∆H  = −720kJ/mole
      Calculate the enthalpy change for the reaction   
      CaO_(s)  +  CO_2(g)   →   CaCO_3(s)    (3mks)
   2. Study the energy cycle below and use it to answer the questions that follow. 
      
      
      1. What name is given to the enthalpy change DH₂  (1mk)
      2. Given that DH₁ = +2237kJ/mole and DH₂ = −2378kJ/mole.  Calculate the value of DH₃    (2mks)     
   3.  
      1. When 1.2g of element W was completely burnt in oxygen and all the heat evolved used to heat 250cm³ of water.   The temperature of the water rose from 22°C to 29°C.  Calculate the RAM of element W.  (Specific heat capacity 4.2j/g^-1k^-1   , density of water 1.0g/cm³ and molar heat of combustion is -560kJ/mole)      (2mks)
      2. STATE two reasons why the molar heat of combustion of the above compound is different from the theoretical value.    (1mk)
      3. Define the term, enthalpy of solution.                                         (1mk)
   4.  
      1. Use the bond energies given below to calculate the heat of reaction  for.
         H_2(g)   +  Cl_2(g)  →    2HCl_(g)    (2mks)
         

         Bond	H - H	Cl - Cl	H - Cl
         Bond energy kJ/mole	435	243	431

      2. Sketch the energy level diagram for the above reaction.  (1mk)
3.  
   1. Starting with Zinc metal, describe how zinc carbonate can be prepared in the lab.  (3mks)
   2. Three immiscible liquids Y, X and Z are such that X is less dense than Z and Y is denser than Z.  Draw a well labeled diagram that can be used to separate the three liquids effectively.  (3mks)
   3. When carbonate of metal T was heated, solid P which turned yellow on cooling was formed.
      1. State the identity of solid P (1mk)
      2. Write a balanced chemical equation to show the effect of heat on the nitrate of silver.              (1mk)
   4. Few drops of ammonium hydroxide were added to copper II sulphate solution in a test tube. 
      1. State the observation made (1mk)
      2. If excess ammonium hydroxide is added to the resultant product above, state the observation made and write the equation for reaction that took place (2mk)
4.  
   1. The table below shows volume of hydrogen gas produced when 0.00167g of zinc granules reacted with excess of dilute HCl 
      

      Time (mins)	0	0.5	1	1.5	2	2.5	3	3.5	4	4.5	5	5.5	6
      Volume (cm3)	0	10	18	24	28	31	34	37	38	39	40	40	40

      1. Plot a graph of volume of hydrogen gas produced against time.  (3mks)
      2. From the graph find the rate of reaction at minute 3.5  (2mks)
      3. Explain why the rate of reaction
         1. Is faster at the beginning of the experiment (1mk)
         2. Remains constant from  the 5^th minute (1mk)
      4. On the same axes sketch a graph for the reaction between the 2g zinc powder and 100cm³ of 2MHCl.  (1mk)
   2. In the production of hydrogen for use in Haber process, carbon (II) oxide is reacted with steam according to the following equations
      CO_(g)   +  H₂O_(g)    CO_2(g)   +  H_2(g)   ∆H=+ve
      1. What name is given to the above type of reaction (1mk)
      2. State and explain the effect of
         1. Removing carbon (IV) oxide from the mixture on the yield of hydrogen.  (1 ½ mks)
         2. Increasing the temperature of the system on the equilibrium mixture.  (1 ½ mks)
5.  
   1. Define the following term Binary electrolyte (1mk)
   2. A form four student from MSHINDI secondary school was given the following list of elements with their reduction potentials.
      

      element	Electrode potential
      G	0.0
      Z	− 0.6
      M	+ 1.82
      V	− 1.9
      Y	+ 0.9
      J	− 2.4

      1. State the possible identity of element G and give a reason for your answer.  (1mk)
      2. Draw a well labelled diagram of the electrochemical cell by combining the half-cells of element Y and J  (3mk)
      3. Calculate the emf of the cell above.  (1mk)
      4. Write the cell representation of a cell made by combining the half-cell of element M and Y.( Take their charges to be ⁺2 respectively.) (1mk)
   3. In the electrolysis of dilute sulphuric (VI) acid using platinum electrode, the volume of hydrogen collected is twice the volume of oxygen collected.  Explain this observation.                         (2mk)
   4.  
      1. A current of 1.3 Amperes was passed through an electrolytic cell containing Copper ii sulphate solution for 2½ hours using graphite electrodes. Calculate the mass of copper deposited at cathode. (Faraday= 96500C, Cu= 63.5)         (2mk)
      2. Apart from the deposition of brown copper metal, state another observation seen during the electrolysis.(1mk)
6. Study the flow chart below and answer the questions that follows 
   
   1. Name the following ( 1½ mk)
      1. Process Q
      2. Process R
      3. Process S
   2. Write equations for the formation Of Fertilizer B  (1mk)
   3. Name the catalyst and give conditions for process R.   
      1. Catalyst                          ( ½ mk)
      2. Conditions                       (1mk)
   4. Study the set up below and answer the questions that follow
      
      1. Write an equation for the reaction that takes place.    (1mk)
      2. Explain the source of red brown fumes.    (1mk)
   5. Describe a chemical test that can be used to distinguish between sulphur IV oxide gas and hydrogen sulphide gas.         (2mk)
7.  
   1. Name the following compounds.  (2mks)
      1. CH₃CH₂COOH      
      2. CH₃CHClCHBrCH₂CH₃     
   2. Use the flow chart to answer the questions that follow
      
      1. Name the following    (1½ mks)
         1. Gas P
         2. Solution C
         3. Substance J
      2. Name the type of reaction involved in the following steps. (1½ mks)
         1. Step I
         2. Step II
         3. Step III
      3. Draw and name the structure of  Polymer K             (2mk)
      4. Write a chemical equation for the reaction taking place during the formation of substance L.      (1MK)
   3.  
      1. Study the structure below
         
         1. Name the structure above.  (1mk)
         2. Draw the structures of the two monomers that make up the above structure.                                                          (2mks)
            HN-(CH2)6-N-C-(CH2)4-C
      2. Below are two cleansing agents. Study them and answer the questions that follow
         B-        R – COONa 
         C -  
         1. Name the class to which cleansing agent B belongs?    (1mks)
         2. Which cleaning agent above is not environmentally friendly?  Explain (2mks)

MARKING SCHEME

1.  
   1.  
      1. 2,8     
      2. 2,8,8
   2.  
      1. U   
      2. S 
   3.  
      • Q has a larger atomic radius than R/ R has a shorter atomic radius Q  1mk
      • R has a greater nucleic charge /protonic charge which attracts the energy levels reducing its size
   4.  
   5. S has a  giant atomic structure with strong covalent bonds while T HAS SIMPLE MOLECULAR STRUCTURE  WITH WEAK VAN DER WAAL FORCES.
   6.  
      1. 2Na +   2H₂O -------------- 2 NaOH  + H₂
         2Q  +  2H₂O ---------------2 QOH  +  H₂
      2. 4Al   + 3O₂  --------------- 2 Al₂O₃  1mk
         MOLES OF OXYGEN GAS   960    = 0.04   ½mk
                                                      24000
         MOLES OF AL₂O₃        O₂;AL₂O₃ 
                                                3      ;  2
                                                 0.04; ?
         0.04 X ² /₃ = 0. 0267   ½ mk
         Mass of AL₂O₃  =    0.0267 X 102= ½mk 
                                        2.7234g  ½ mk
2.  
   1. CaO………………..Ca+ ½O₂     +635
      CO₂………………….C + O₂       +394       
      Ca + 1½O₂ …………CaCO₃      −720
                                       = +309
   2.  
      1. DH Hydration 
      2. DH₃ = DH₁ + DH₂
         +2237 − 2378 = −141
   3.  
      1. MCDT   M= 250, C= 4.2 ,DT= 29 − 22 =  7
         250 X 4.2 X 7 = 7.35kJ
                 1000
         If 1.2g= 7.35
                 ?= 560
         1.2 x 560 = 91
             7.35
      2.  
         • Incomplete combustion of the compound.
         • Heat loss to the surrounding
      3. The enthalpy change when one mole of a substance is dissolved in water to form the most dilution solution possible/an infinitely dilute solution.
   4.  
      1. H-H  + Cl –Cl ---------2H-Cl
         +435 + 243  --------------2( -431)  1MK
         678 – 862=  -184 Kj  1mk
      2. exothermic , reactants above, products below, arrow facing down.
         
3.  
   1.  
      • React zinc metal with dilute nitric v acid, stir until effervescence stops.
      • Filter. React the zinc nitrate solution formed with sodium carbonate to form insoluble zinc carbonate. Filter, rinse the residue with distilled water and dry between filter papers. 
   2. Nb/ separating funnel  - 1MK
      correct order of liquids- X,  Z, Y
      
      Beaker---------------- ½
      Stand ---------------- ½   
   3.  
      1. Lead oxide
      2. 2AgNO_3(aq)………………2Ag_(aq) + 2NO_2(g) +O_{2(g )}      
   4.  
      1.  A blue precipitate is formed. 1mk
      2. Blue ppt dissolves forming a deep blue solution. 1mk
         Cu (OH)_2(s) +4NH_3(aq) …………..[Cu(NH₃)₄]⁺² _(aq) +2OH⁻ _(aq)
4.  
   1.  
      1. x-axis with correct  units½ 
         Y-axis with correct units ½
         Plotting- 13 points- 1mk
                       12 points – ½ mk
                        11points and below- 0mk
      2. tangent- 1mk    dy/dx= ½    correct answer with units ½ 
      3.  
         1. the reactants are at a higher  concentration in the beginning thus more particles hence higher chances of collision 1mk
         2. all the zinc has been used up and therefore reaction has come to an end.1mk
      4. curve should start and level off at the same time with the other one but is ABOVE IT.
   2.  
      1. Reversible reaction
      2.  
         1. The yield would increase.1MK Removing co2 would favor the forward reaction forming more hydrogen.
         2. Equilibrium shifts to the right. 1mk The forward reaction is endothermic and therefore would be favored by an increase in temperature
5.  
   1. an electrolyte that contains only one cation and one anion.
   2.  
      1. Hydrogen. ½  It has an electrode potential of 0.0v ½ mk
      2.  
         
      3. EREDUCED - EOXIDIZED
         + .9 − −2.4  =  ½
         0.9 +2.4= 3.3V
      4. Y/Y⁺² (aq) // M⁺²  (aq)/M(S)
   3. The electrons lost at anode must be the ones gained at cathode 1 mk , 4 electrons are lost at anode to form 1 mole of oxygen, when the four electrons are gained at cathode, 2 moles of hydrogen are formed1mk
      also accept correct equations;
      4OH⁻ (aq)   ------------ 2H₂O  +  O₂  + 4e⁻
      4H⁺ (aq) +   4e⁻ ----------------   2H₂ (g)
      Both equations must be correct to score two mks
   4.  
      1. Q=IT   1.3X 2.5 X60 X 60= 11,700C 1mk
         63.5g of Cu= 2Faradays
         If 63.5g ---------- 2 x96500
               ?      ------------ 11700
         63.5 x 11700 ½ mk=   3.8494g ½ mk
            2x 96500
      2.  
         • blue color of solution fades.
         • bubbles of a colorless gas
6.  
   1.  
      1. Electrolysis
      2. Haber
      3. Frasch
   2. 2NH_3aq + H₂SO_4aq → ( NH₄)₂SO₄ aq
   3.  
      1. finely divided iron  ½ mk
      2.  
         • Temp   --450°c  ½ mk
         • Pressure   200- 250 atm  ½ mk
   4.  
      1. 4NH₃  + 5O₂----------- 4NO  + 6H₂0
      2. The NO produced is readily oxidized to NO₂ 
   5.  
      • Bubble a sample of each gas into acidified potassium manganite (vii), 1mk
      • In both purple acidified KMnO₄ will turn colorless but with H₂S there will be a yellow deposit. 1mk
7.  
   1.  
      1. Propanoic acid
      2. 3-Bromo-2-Chloro-pentane
   2.  
      1.  
         1. Hydrogen
         2. Magnesium propanoate
         3. Propane
      2.  
         1. I -hydrogenation
         2. II- dehydration
         3. III – esterification
      3. polypropene.
      4. CH₃CHCH₂ + HBr--------- CH₃CH₂CHBr
   3.  
      1. nylon 6,6
      2. NH₂ (CH₂)₆NH₂ 1MK and HOOC (CH₂)₄COOH 1MK
      3.  
         1. Soap detergents
         2. C  1mk, it is non-biodegradable 1mk