Chemistry Paper 2 Questions and Answers - Momaliche Joint Pre Mock Exams 2022

QUESTIONS

1. Use the information below on standard electrode potentials to answer the questions that follow
   Electronic reaction                       EƟ volts
   C2+ (aq) + 2e-        C(s)               +0.34
   D2+ (aq) + 2e-         D (s)            +0.44
   E+ (aq)   + e-           E (s)             -2.92
   F2+ (aq)  + 2e-         F (s)             -2.71
   G2+(aq) + 2e-         G(s)              -0.14
   ½H2 (g) + e-           H- (aq)         +2.87
   ½K2 (g)  + e-              K-(aq)      +1.09
   L+ (aq)    +  e-         ½L2(aq)      0.00 
   1.      
      1. Identify the strongest reducing agent and oxidizing half cells. Give reasons(2mks)
      2. Calculate the emf of the cell obtained by connecting half cells C and D(1mk)
   2. Draw a well labeled diagram of a cell formed by connecting half cells E and D. on the diagram indicate the flow of electron (3mks)
   3. The figure below shows the electrolysis of dilute sulphuric (VI) acid
      
      1. On the diagram label the cathode and anode (1mk)
      2. Name the gases U and V  (1mk)
         Gas U
         Gas V 
      3. Write the equation taking place at the anode    (1mk)
   4. Define electrolysis and state any two applications of electrolysis   (3mks)
2.      
   1. The flow chart below outlines some of the processes involved during extraction of copper from copper pyrites. Study it and answer the questions that follow. 
      
      1. Name gas K (1mk)
      2. Write an equation for the reaction that takes place in the 1st roasting furnace (1mk)
      3. Write the formula of the cation present in slag M    (1mk)
      4. Identify gas P (1mk)
      5. What name is given to the reaction that takes place in chamber N? Give a reason for the answer  (1mk)
   2. The copper obtained from chamber N is not pure. Draw a labeled diagram to show the set up you would use to refine the copper by electrolysis   (2mks)
   3. Give two effects that this process could have on the environment  (2mks)
3.      
   1. The grid below represents part of the periodic table. Study the information and answer the questions that follow. The letters do not represent the actual symbol of the elements.
      
      1. Which element would form a trivalent cation?  1mk)
      2. Write the equation for the reaction that would occur between E and Y(1mk)
      3. Which elements belong to the region labeled W?  (1mk)
      4. Which is the most reactive non-metallic element in the table above? Explain   (2mks)
      5. How does the atomic radius of T compare with that of Y  (2mks)
   2. The table below shows some properties and electronic arrangements of common ions of elements represented by letters D to K. Study the information and answer the questions that follow>
      

      Element	Formula of ion	Ionic electronic arrangement	Atomic radius (nm)	Ionic radius (nm)
      D	D-	2.8	0.072	0.136
      E	E+	2.8.8	0.231	0.133
      F	F3+	2.8	0.143	0.050
      G	G2+	2.8.8	0.133	0.074
      H	H2+	2.8	0.160	0.064
      I	I+	2.8	0.186	0.095
      J	J3+	2.8.8	0.110	0.190
      K	K-	2.8.8	0.099	0.181

      1. State the atomic numbers of elements F and G   (1mk)
      2. Select two metals that belong to period 3 (1mk)
      3. Element I reacts violently with water. Write the equation for the reaction. (1mk)
      4. Why is the ionic radius of G smaller than its atomic radius  (1mk)
      5. Compare and explain the reactivity of G and H   (2mks)
4. In an experiment to study the rate of reaction between duralumin (an alloy of aluminum, magnesium and copper) and hydrochloric acid, 0.5 g of the alloy were reacted with excess 4M hydrochloric acid. The data in the table below was recorded. Use it to answer the questions that follow.
   

   Time (minutes)	Total volume of gas (cm3)
   1	0
   2	220
   3	410
   4	540
   5	620
   6	640
   7	640

   1.        
      1. On the graph paper provided plot a graph of total volume of a gas produced against time (3mks)
      2. From the graph determine the volume of gas produced at the end of 2½ minutes  (1mk)
   2. Determine the rate of reaction between the 3rd and 4th minute(1mk)
   3. Give a reason why some solid remained at the end of the experiment  (1mk)
   4. Given that 2.5cm³ of the total volume of the gas was from the reaction between magnesium and aqueous hydrochloric acid, calculate the percentage mass of aluminium present in 0.5 g of the alloy. (Al = 27, and molar gas volume = 24000cm³ at 298K)(3mks)
   5. State two properties of duralumin that makes it more suitable than aluminum in aero plane constructio(2mks)        
5. The flow chart below is for the manufacture of sodium carbonate using Solvay process. Use it to answer the questions that follow
   
   1. Name :
      1. Gas W (1mk)
      2. Solution H    (1mk)
      3. Solid X   (1mk)
      4. The product J (1mk)    
   2. Write an equation for the reaction in chamber B  (1mk)                                   
   3. Name two raw materials used in Solvay process    (2mks)
   4.    
      1. Name one substance recycled in Solvay process    (1mk)
      2. Give two reasons why CO₂ is used as fire extinguisher   (2mks)
      3. Explain why lead carbonate is not reacted with dilute H₂SO₄ in preparation of CO₂ in the laboratory (2mks)
6.      
   1. Name four components of crude oil  (2mks)
   2. What is the difference between thermal cracking and catalytic cracking?  (2mks)
   3. Study the flow chart below and answer the questions that follow.
      
      
      1. Identify process W and X (1mk)
      2. Name substances B and C   (1mks)
      3. Write the equation for the reaction leading to production of substance A       (1mk)
      4. Substance B was completely burned in air. Write the equation for the reaction  (1mk)
      5. State and explain the observations made when bromine is added to a das jar full of substance B in the presence of sunlight. (2mks)
      6. The polymer D has a relative molecular mass of 112,000. Calculate the value of n (C=12, H = 1) (2mks)
7.      
   1. What is meant by molar heat of combustion?  (1mk)
   2. State the Hess’s law  (1mk)
   3. Use the following standard enthalpies of combustion of graphite, hydrogen and enthalpy of formation of propane.
      ∆HƟC (Graphite) = -393kJ/mol
      ∆HƟC (H_2(g))  =  -286kJ/mol
      ∆HƟf  ( C₃H₈) = -104kJ/mol
      1. Write the equation for the formation of propane  (1mk)
      2. Draw an energy cycle diagram that links the heat of formation of propane with its heat of combustion and the heats of combustion of graphite and hydrogen  (3mks)
      3. Calculate the standard heat of combustion of propane   (1mk)
      4. Other than the enthalpy of combustion, state one factor which should be considered when choosing a fuel (1mk)
      5. The molar enthalpies of neutralization for dilute hydrochloric acid and dilute nitric (V) acid are -57.2kJ/mole while that of ethanoic acid is -55.2kJ/mol. Explain this observations. (2mks)

MARKING SCHEME

1.      
   1.      
      1. Strong  reducing agent →E ; highest –ve volts
         Strong oxidizing agent → H₂ ; higher +ve volts
      2. Ecell = 0.44- 0.34 =+ 0.10V
         
   2. Shown on the diagram
   3. Gas U → hydrogen gas ½
      Gas V → oxygen gas ½
   4. 4OH-(aq) → 2H₂O(l) + O_2(g) + 4e-  
   5. Electrolysis is passage of electric current through an electrolyte hence decomposing it
      • Electroplating
      • Extraction of metals
      • Purification of metals
      • Manufacture of NaCl, Cl₂, and H₂
        Any 2 carry each one mark
        SUB-TOTAL 12
2.    
   1.    
      1. Sulphur (IV) oxide   
      2. 2CuFeS_2(s) + 4O_2(g) → 2FeO(s) + Cu₂S(s)  + 3SO_2(g) 
      3. Fe2+   
      4. P is carbon (IV) oxide 
      5. Reduction – oxidation (redox) reaction
         This is because copper (I) oxide (Cu₂O) is reduced to copper while coke is oxidized to carbon (IV) oxide.
   2.      
      
   3.    
      1. Acid rain may form due to presence of sulphur (IV) oxide (SO₂) and carbon (IV) oxide
      2. Dumping of the waste like the slag prevent vegetation growth
      3. Large gullies left after the ore is excavated destroys the environment 
         Any solution with Cu²⁺ i.e CuSO₄, Cu(NO₃)₂, CuCl₂
         3mks
         Any two correct award 1 mark each
         SUB-TOTAL 9
3.      
   1.      
      1. Element S   
      2. E(s) + Y_2(g)→ EY_2(g)
      3. Transition metals 
      4. Y  √ 1; it has the highest ability to attract electrons√
      5. Y is smaller than T. √1  since Y has greater nuclear charge than T √1 OR it has many protons than T
   2.      
      1. F ½  atomic number 13
         G ½ atomic number 20
      2. F ½ and H ½  OR F and I OR H and I
      3. 2I(s) + 2H₂O (l) → 2IOH(aq) + H_2(g)
         NB: Penalize accordingly IF NOT balanced; ½ missing symbols
      4. The ion has one energy level √ 1  less than H. G loses its valence electrons with much ease than H
      5. G is more reactive than H. G loses its valence electrons with much ease than H  
         SUB-TOTAL 13
4.    
   1.    
      1. NB: scale√1
         Plot √1
          Axis√1
      2. V = 325cm³√ NB,must be shown on the graph for full mark
   2. (540-410)÷60√ = 2.16cm³/sec√
   3. Some solid remained due to presence of unreacted copper √½ since copper is below hydrogen in the reactivity series √½
   4. Volume of hydrogen = 640-2.5 = 637.5cm³√ ½
      moles of hydrogen = 637.5÷24000 = 0.02656√ ½
      mole ratio Al : H₂ = 2:3 based on equation
      moles of Al = 0.02656 x 2/3 = 0.0177 √½
      mass of Al = 0.0177 x 27 = 0.478 g√ ½
      % Al = (0.4748÷0.5) x 100 = 96.625% √½
   5. It is cheaper than pure Aluminum
      It is harder than Aluminum
      Lighter than Aluminum 
      Any two
      SUB-TOTAL 11
5.    
   1.    
      1. Ammonia 
      2. Ammonium chloride
      3. Sodium hydrogen carbonate 
      4. Calcium chloride/ water
   2. 2NH₄Cl(aq) + Ca(OH)_2(aq)  → CaCl_2(aq) + 2H₂O (l) + 2NH_3(g) 
   3. carbon (IV) oxide√/ calcium carbonate√/ Brine√/Ammonia√            
   4.    
      1. G; Carbon (IV) oxide / ammonia/ water             
      2. Its denser than air
         does not support combustion
      3. There would be formation of PbSO₄  ½ which is insoluble ½
         This insoluble PbSO₄ coats  ½ the lead carbonate thus stops further reaction ½
         SUB-TOTAL 12
         Any one carry 1 mark
6.    
   1. Lubricating oil, fuel oil, diesel, kerosene, petrol, bitumen, gasoline, naptha, 
   2. Thermal cracking is breaking down long chain alkanes using high temperatures
   3. Catalytic cracking involves breaking long chain alkanes at lower temperatures in the presence of catalysts
   4.    
      1. W → Fermentation ½
         X→  Distillation ½
      2. B→ Ethane ½
         C→ sodium ethanoate ½ 
      3. C₂H₅OH →C₂H4 (g) + H₂O (l)
                     H₂SO4
      4. 2C₂H_6(g) + 5O₂ (g)   →  4CO₂ (g) + 6H₂O (l) 
      5. Brown/Yellow/Red  bromine is decolorized in the presence of sunlight; substitution reaction takes place
      6. RMM of ethene = 28½
                  28n = 112000  ½
                  n = 112000÷28 ½
                     = 4000 ½
         Any four ½ each
7.      
   1. Is the heat given out when one mole of a substance burns completely in air
   2. Enthalpy change for a reaction is the same whether the change is brought about in one step or through various intermediate steps. OR
      The energy changes in converting reactants to products is the same regardless of the route by which the chemical change occurs.
   3.    
      1. 3Cu(s) + 4H_2(g)  → C₃H_8(g) 
                                  ∆H1 
      2. 3C (s) + 4H_2(g)  →  C₃H_8(g)
            ∆H₂        ∆H₃          ∆H₄    
         3CO_2(g)  + 4H₂O(l)
      3. ∆H₄ = ∆H₂ + ∆H₃ - ∆H₁
         = ( -393 X3) + (-286x4) – (-104) ½
         = -2219kJ/mol ½
   4. Polution/heating value/availability/cost       
   5. The enthalpy of neutralization of ethanoic acid is less than√ ½that of HCl and HNO₃. This is because ethanoic acid is a weak acid ½ hence ionizes partially½  and some energy is used to ionize it fully ½