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

QUESTIONS

1.    
   
   1. The diagram below shows part of the processes in the manufacture of Nitric (V) acid
      
      
      1. Explain the role of the purifier (1mk)
      2. State the pressure used in the compressor (1mk)
      3. State two functions of the heat exchanger (1mk)
      4. Name the catalyst used in the catalytic chamber (1mk)
      5. Write equation of the reaction that takes place in:
         1. Catalytic chamber (1mk)
         2. Reaction chamber (1mk)
         3. Absorption tower (1mk)
   2. Calculate the volume of Oxygen that would be obtained from the decomposition of 21.25g of Sodium Nitrate at s.t.p (1 mole of a gas occupies 22.4dm³ at stp, N=14, Na=23,O=10) (3mks)
      
   3. Name two commercial uses of Nitric (V) acid (2mks)
2. In an experiment to investigate the solubility of solid Y and Z, the following results were obtained.
   

   Temperature ºC	0	10	20	30	40	50
   Solubility of solid Y (g/100g of water)	8	13	24	38	61	98
   Solubility of solid Z (g/100g of water)	28	32	35	38	42	46

   1. What do you understand by the term solubility? (1mk)
   2. On the grid provided, plot a graph of solubility of Y and Z against temperature (on the x-axis). (4mks)
   3. From your graph determine
      1. The solubility of Y at room temperature (25ºC) (1mk)
      2. The temperature at which solubility of Y is 45g/100g of water. (1mk)
   4. If a solution of Y contains 35g of solid in 100g of water is cooled from 40ºC, Determine
      1. The temperature at which the crystals will first form (1mk)
      2. The mass of crystals deposited if the solution is cooled to 5ºC (1mk)
   5. Compare the solubilities of Y and Z in water. (2mks)
   6. Give one application of solubilities. (1mk)
3. Study the flow chart below and answer the questions that follow.
   
   Residue M was yellow when hot and white when cold.
   1. 
      
      1. Identify.
         1. White precipitate K ______________________________ (1 mark)
         2. Solution N _______________________________ (1 mark)
         3. Residue M ________________________________ (1 mark)
      2. Write an ionic equation for the reaction of solution N with Pb(NO₃)_2(aq). (1 mark)
      3. Write observations that would be made when ammonia solution is added dropwise till in excess to the colourless solution N. (1 mark)
   2. Ammonia gas bubbled into water forms a solution which conducts electricity whereas the solution formed when it is bubbled through methylbenzene does not. Explain. (2 marks)
   3. Boilers used for boiling hard water are normally covered with boilers scale after sometime.
      1. What is the chemical name for boilers scales? (1 mark)
      2. How is the boiler scale removed? (1 mark)
   4. Write the formula of the anion in solution J. (1 mark)
4.    
   1. Name each of the processes described below which takes place when salts are exposed to air for sometime.
      1. Anhydrous copper (II) sulphate becomes wet. (1 Mark)
      2. Common table salt forms an aqueous solution (1 Mark)
      3. Fresh crystals of sodium carbonate Na2CO₃.10H₂0 becomes covered with white powder of formula Na2CO₃.H₂O (2 Marks)
   2. Write the formula of the complex ion formed in each of the reactions described below.
      1. Zinc metal dissolves in hot alkaline solution (1Mark)
      2. Copper hydroxide dissolves in excess ammonia solution (1Mark)
   3. A hydrated salt has the following composition by mass. Iron 20.2%, Oxygen 23%, Sulphur 11.5% and water 45.3%. Its relative formula mass is 278
      1. Determine the formula of the hydrated salt. (3Marks)
         (Fe = 56, S = 32, O = 16, H = 1)
      2. 6.9g of the hydrated salt was dissolved in distilled water and the total volume made to 250cm³ of solution. Calculate the concentration of the salt solution in moles per litre. (2Marks)
   4. Describe how a solid sample of lead (II) chloride can be prepared using the following reagents:- dilute nitric acid, dilute hydrochloric acid and lead carbonate. (3 Marks)
5.    
   1. The set up below was used to prepare dry hydrogen gas.
      
      
      1. Complete the diagram to show how dry sample of hydrogen gas can be collected. (3mks)
      2. Hydrogen gas is used in hardening of oils into fats during the manufacture of margarine. Give two conditions necessary for the process to occur. (2mks)
      3. Give a reason why the following are not used in preparation of hydrogen gas in the lab(2mks)
         1. Magnesium metal
         2. Iron
      4. Write the formula of the substance added in preparation of hydrogen to make the reaction proceed faster (1mk)
      5. Other than hardening of oils, state two other uses of hydrogen. (1mk)
   2. In an experiment to determine the proportion of oxygen in air, copper turnings were packed in excess along a combustion tube connected to two syringes of 120cm³ each in volume. Syringe R contained 120cm³ of air while syringe S was empty as shown.
      
      Air was passed over the heated turnings slowly and repeatedly until there was no further change in volume. 95.5cm³ of air remained in syringe R.
      1. Why was air passed over heated copper slowly and repeatedly. (1mk)
      2. State one observation made in the combustion tube during the experiment. (1mk)
      3. Determine the percentage of oxygen used during the experiment. (1mk)
6. Use the table below to answer the questions that follow.
   (The letters are not the actual symbols of the elements )
   

   Element	Atomic number	Melting point (ºC)
   A	11	97.8
   B	13	660
   C	14	1410
   D	17	-101
   E	19	63.7

   1. Write the electronic arrangement for the ions formed by the elements B and D
   2. Select an element which is
      1. a poor conductor of electricity __________________________________( ½ mark )
      2. most reactive metal ________________________________ ( ½ mark)
   3. Explain briefly how the atomic radii of element B and C compare. (2 marks )
   4. Use dots (⋅) and crosses (x) to represent outermost electrons and show the bonding in the compound formed between C and D. ( 2 marks )
   5. Explain why the melting point of element B is higher than that of element A. (2 marks )
   6. Write an equation for the reaction that takes place between element A and water. (1 mark )
   7. Describe how a solid mixture of the sulphate of element E and lead (II) sulphate can be separated into solid samples.(3 marks)
7.      
   1. Give the systematic names for following compounds;
      1.                O
                        II
         CH₃CH₂ C – O - CH₂CH₃ (1mk)
      2. CH₂CHCHCH₂ (1mk)
   2. Study the flow chart below and use it to answer the question that follow
      
      
      1. Name:
         Substance A (½mk)
         Process I (½mk)
         Substance B (½mk)
         Gas C (½mk)
         Substance D (½mk)
         Compound E (½mk)
      2. If 144kg of sugar (C₆H₁₂O₆) was used to produce ethanol in this process, calculate the mass in kg of ethanol produced (C=12,H=1, O=16) ( 3 marks )

MARKING SCHEME

1.      
   1.    
      1. To remove dust particles√ - than would otherwise “poison”  that catalyst (1mk)
      2. 9  atmospheres √1(1mk)     
      3. To pre heat NH₃ and air to an optimum temperature (reactants)
         To cool No (product) (2mks)
      4. Platinum –Rhodium  catalyst (1mk)
      5.      
         1. 4NH_3(g) +5O_2(g) → 4NO(g) +6H₂O(g) (1mk)
         2. 2NO(g) +O_2(g)→ 2NO_2(g)(1mk)
         3. 4NO_2(g)+ O_2(g) +2H₂O(l) → 4 HNO_3(aq)  
   2.      
      1. 2NaNO_3(S) → 2NaNO₂(g) +O_2(g)
         NaNO₃ = 23 + 14 + 48 =85
         Moles of NaNO₃ = 21.25
                                          85
         Moles of O₂ ⇒ ½ x 0.25
         = 0.125
         Volume  of O₂  ⇒ 09.125 x 22.4
         = 2.8dm³
         V = 280 cm³
      2. Manufacture of fertilizers
         Manufacture of explosives
         Manufacture dyes and drugs
         Purification of metals eg.silver and gold
         Etching designs on some metals
2.    
   1. This is the maximum mass of salt/solute that can saturate 100g of water at a given temperature.
   2.    
      
   3.    
      1. 30g of H₂O Accept 36g/100g water
      2. 33.5ºC
   4.    
      1. Sol at 40ºC = 61g/100g H₂O
         At 27ºC
      2. Sol at 40ºC = 61g/100g H₂O
         Sol at 27ºC = 35g/100g H₂O
         Sol at 5ºC = 10g/100g of H₂O
   5. Y is more soluble than Z
      Y dissolves better at higher temperatures than Z
   6. Fractional crystallization – Separation of mixtures with different solubilities
3.    
   1.    
      1.    
         1. Zn(OH)₂
         2. ZnCl₂
         3. ZnO
      2. Pb2+(aq) + 2Cl(aq) → PbCl2(s)
      3. White precipitate soluble in excess. 
   2. Ammonia gas is polar and ionizes in water which is polar.  
      While it does not ionize in methylbenzene which is non polar.
   3.    
      1. Calcium carbonate/magnesium carbonate.
      2. Passing a solution of dilute hydrochloric acid or nitric (V) acid in the boiler. (1mk)
   4. [Zn(OH)₄]^2-
4.    
   1.    
      1. Hygroscopy
      2. Deliquescence
      3. Efflorescence
   2.    
      1. [Zn(OH)₄]^2-    ii. [Cu(OH)₄]^2-
         

         Fe	S	O	H2O
         20.2	11.5	23.0	45.3
         56	32	16	18
         0.36	0.36	1.44	2.52
         1	1	4	7

         (FeSO₄.7H₂O)=278
         278n=278
         n=1
         Formula FeSO₄.7H₂O
      2. No. of moles ^6.95/₂₇₈=0.025moles
         0.025moles-250cm³
                             1000
         0.025x1000=²⁵/₂₅₀=0.1mole/litre 
               250
   3.     
      • Add exess lead carbonate to dilute HNO₃,
      • shake and filter to remove unreacted carbonate  
      • Add excess dilute HCl to the mixture
      • Filter to obtain lead(II) chloride as the residue
      • Rinse and Dry between filter paper to obtain solid PbCl₂
5.    
   1.    
      1.    
         
      2. Catalyst Nickel
         Temperature 150ºC to 250ºC
      3. magnesium is very expensive
         it gives a mixture of gases including bad smelling and poisonous hydrogen sulphide
         CuSO₄. 5H₂O
      4.    
         • Manufacture of ammonia
         • Manufacture of hydrochloric acid
         • Welding and cutting of metals
         • Rocket fuel and in fuel cells.
   2.    
      1. Slowly to allow ample time for reaction repeatedly to ensure all active air (oxygen) is used up
      2. The brown copper turnings slowly changed black.
      3. 120 - 95.5 x 100
             120
         24.5 x 100 = 20.41667%
             120
6.      
   1. B – 2 : 8
      D – 2 : 8 : 8
   2.    
      1. D
      2. E
   3. Atomic radius of B is larger than that of C. C has more protons. The outer energy level electrons are pulled strongly to the nucleus reducing the atomic size. 
   4.    
      
   5. Element B has stronger metallic bond ( has more delocalized electrons ) than A, hence higher amount of heat energy is needed to break the bond.
   6. 2A(s)  +  2H₂O (l) → 2AOH (aq) +  H₂ (g)
      Reject fully if unbalanced
      Award ½ mk if states are missing or any one state is wrong. 
   7. Add water to the mixture and stir.
      Filter to obtain lead (II) sulphate as residue and sulphate of E as filtrate 
      Dry the residue to obtain lead (II) sulphate.
      Evaporate the filtrate to dryness to obtain the solid sulphate of E.
7.    
   1. Ethylpropanoate
   2. But-2,3-diene
   3.      
      1. A  - yeast 
         I   - fractional distillation
         B  - Sodium ethoxide 
         C -  Hydrogen
         D -  Ethene
         E – polyethene / polythene(4mks)
      2.    
         1. C₆H₁₂O₆→2C₂H₅O +2CO₂ 
         2. nfm = 2 x 12 + 6 + 16 = 46
            massofethanol = 46 x 1600
            1000
            =73.6kg
            (3mks)