Chemistry Paper 2 Questions and Answers - Form 4 Mid Term 2 Exams 2021

CHEMISTRY
PAPER 2
FORM 4 MID TERM 2

INSTRUCTIONS

• Answer all questions

1.      
   1. Name the method that can be used to obtain pure iron(III) chloride from a mixture of iron(III)b chloride and sodium chloride (1 mk)
   2. A student was provided with a mixture of sunflower flour, common salt and a red dye. The characteristics of three substances in the mixture are given in the table below.
      

      substance	Solubility in water	Solubility in ethanol
      Sunflower flour	Insoluble	Insoluble
      Common salt	soluble	Insoluble
      Solid red dye	soluble	soluble

      
      The student was provided with ethanol and any other materials needed.
      Describe how the student can separate the mixture into its three components.(3mks)
   3. The diagram below shows a part of a periodic table. The letters do not represent the actual symbols of elements. Use the diagram to answer the question that follow.
      
      1. Explain why the oxidizing power of W is more than that of x 2mks
      2. How do the melting points of R and T compare? Explain.(2mks)
      3. Select an element that could be used
         1. In weather balloons(1mk)
         2. For making a cooking pot.(1mk)
   4.         
      1. Classify the substances water, iodine diamond and candle wax into elements and compound (2mks)
         

         Element	Compound

      2. Give one use of diamond.
2. The flow chart below shows some of the processes involved in larger scale production of sulphuric (vi) acid. Use it to answer the questions that follow. questions that follows.
   
   
   1. Describe how oxygen is obtained from air in large scale.(3mks)
   2.    
      1. Name substance A.(1mk)
      2. Write an equation for the process that takes place in the absorption camber (1mk)
   3. Vanadium (V) oxide is commonly used catalyst in the contact process.
      1. Name another catalysts which can be used for this process.(Imk)
      2. Give two reasons why vanadium (v) oxide is the commonly used catalyst (2mks)
   4. State and explain the observation made when concentrated sulphur(vi) acid is added to crystals of copper (II) sulphate in a beaker (2mks)
   5. The reaction of concentrated sulphuric (VD) acid with sodium chloride produces hydrogen chloride gas. State the property of concentrated sulphuric (VI) acid illustrated in this reaction(Imk)
   6. Name two types of sulphuric (vi) acid. (2mks)
3. At 25ºC 50g of potassium nitrate were added to 100g of water to make a saturated solution.
   1. What is meant by saturated solution (1mk)
   2. The table below gives the solubility of potassium nitrate at different temperatures.
      

      Temp C	12	20	28	36	44	52
      Solubility  g/100g of water	22	31	42	55	70	90

      
      
      1. Plot a graph of the solubility of potassium nitrate (vertical axis) against temperature. 3mks)
      2. Use the graph.
         1. Determine the solubility of potassium nitrate at 15'c (1mk)
         2. Determine the mass of potassium nitrate that remained un dissolved given that 80g of potassium nitrate were added to 100cm of water and warmed to 40°C.(Qmks)
   3. Determine the molar concentration of potassium nitrate at 15 C.(Assume there is no change in density of water at this temperature). (K=39.0 N=14.00 = 16.0)3mks)
4. Study the chart below and answer the questions that follow.
    
   
   1. Name substance
      1. P (1mk)
      2. Colourless gas M (1mk)
   2. Write an ionic equation for the reaction producing solid p-(1mk)
   3.      
      1. Write the chemical formula of the complex ion in solutions.(Imk)
      2. In the preparation of carbon (iv) oxide in the laboratory dilute hydrochloric acid was added to marble chips (CaCO₃) as shown in the diagram below.
         
         
         1. What observation is made when the acid is added to the marble chips.(1 mk)
         2. Why is dilute hydrochloric acid preferred to dilute sulphuric (vi) acid in the above reaction.(2 mks)
         3. Explain why the gas was passed through water in apparatus L.(imk)
         4. Calcium hydroxide is used to test carbon (iv) oxide but not sodium hydroxide Explain(2mks)
5.     
   1. The combustion of propane can be represented by the following equation.
      C₃H_8(g) +5O_2(g) → 3 CO_2(g) + 4H₂O_(l)
      1. Define the molar enthalpy of combustion of a compound (1mk)
      2. Use the thermo chemical equations below to answer the following question.
         1. C_(graphite) + O_2(g) → CO₂ H₁ = 393.5 Kj Mol^-1
         2. H_2(g) + ½O_2(g) → H₂O_(l) ΔH₂= -285.8 Kj mol^-1
         3. 3C + 4H₂ → C₃H₈ ΔH₃ = 103.7 kg mol^-1
   2.       
      1. Name the type of enthalpy change represented by AH (1mk)
      2. Draw an energy level diagram for the reaction represented by equation 1.(3mks)
      3. Calculate the molar enthalpy of combustion of propane (3mks)
      4. The enthalpy information of ethanol (CH₃ CH₂ OH) is 3239 KjMol^-1. Use the bond energies given below to calculate the bond energy of formation of O-H.
         C-C = -346 KJ mol^-1
         C-H=414 kJ mol^-1
         C-O=-360 KJ mol^-1 (3mks)
6.           
   1. The diagram below shows a set up in a experiment to prepare chlorine gas and react it with aluminum foil. Study it and answer questions that follow.
      
      
      1. In the experiment, concentrated hydrochloric acid and potassium manganate (VII) were used to prepare chlorine gas. State two precautions that should betaken in carrying out this experiment.(2mks)
      2. Write a balanced equation for the reaction that took place in the round bottom flask (1mk)
      3. Write the formula of another compound that could be used instead of potassium manganate(VII).(Imk)
      4. Explain why it is necessary to allow the acid to drip slowly onto potassium manganate (VII) before the aluminium foil is heated.(1mk)
      5. Write a balanced chemical equation for reaction taking place in combustion tube. (1mk)
      6. State the property of the formed in the combustion tube that makes it possible for it to be collected in the receiver.(1mk)
   2. A student set-up apparatus as shown to prepare and collect dry ammonia gas
      
      
      1. Identify two mistakes in the set-up
         1. Mistake
            Reason
         2. Mistake
            Reason
      2. Name a suitable drying agent of Ammonia(1mk)
      3. Write a balanced chemical equation for the formation of ammonia gas (1mk)
      4. Describe a chemical test for ammonia gas.(Imk)
7. Study the flow chart below and answer the questions that follow
   
   
   1. Identify substances
      A
      B
      F
      G
      4mks
   2. Write down the equation for the formation
      1. Substance C
      2. E and F
      3. Gas G
         3mks
   3. Substance D was found to have a molecular mass of 42000 Determine the number of molecules present in the substance (H=1=12) 2mks
   4. State;
      1. The condition necessary for the conversion of ethanol to substance A.(Imk)
      2. The catalyst required in the conversion A and B.(1mk)

MARKING SCHEME

1.     
   1. Sublimation
   2.    
      • Put the mixture of sunflower, common salt and solid red dye in ethanol. Sunflower and common salt are soluble. Soild red dye dissolves.
      • Add water to the mixture of common salt and sunflower flour. Common salt dissolves. Sunflower flour will not
      • Crystalize the filtrate of common salt and soli-red dye in ethanol.
   3.      
      • Element W has smaller radius than of X. The electron affinity oW is higher than that of X.
      • The melting point of T is higher thna R. Atoms of T are bonded by strong covalent bonds, atoms of R are bonded by metallic bond, which is not as strong as covalnet bond.
      • Q
      • W
   4.      
      1.         
         • Iodine -water
         • Diamond-Candle wax
      2.    
         • Making a drilling machine
         • Making of jewelry      
2.            
   1.             
      1. Pass the air through filter to remove dust particles/ smoke particles or through a selective precipitation.
      2. The remaining gases consists of N₂, O₂, CO₂ and traces of noble gases. Pass the mixture through NaOH, KOH solution to remove CO₂
      3. N₂, O₂ and traces of Noble gases are passed through fractional distillation of liquid air.Difference in BP of N₂, O₂ and noble gases separate them.
   2.                
      1. Sulphuric(vi) acid
      2. H₂SO_4(aq) + SO_2(g) → H₂S₂O_7(l)
   3.                 
      1. Platinum- rhodium catalyst
      2.          
         • It is not easily poisoned.
         • It is cheap
   4. Blue crystal of copper(ii) sulphate turns white. Conc H₂SO₄ isa drying agent.
   5. Oxidising agent
      • Manufacture of fertilizers
      • Processing of metal ores
      • Manufacture of detergents
      • Manufacture of plastic
      • Manufacture of dyes and paints
      • Used in lead-acid accumulators.
3.             
   1. Saturated solution is a solution that canot dissolve any more solute ata a given temperature.  
   2.           
      1. 
            
      2.          
         1. 25g/100g of water
         2. 80g/100g
            40ºC solubility of KNO₃=62g/100g of H₂O
            80-60=20g
      3. at 15ºC solubility= 25g/100g of water
         Relative molar mass of KNO3:
         K=34
         N=14
         3O=48
               101
         25/101= 0.2475 moles of 100cm3
         x → in 1000
         x= 1000 x 100 x 0.2475
                      100
         =2.475m
4.       
   1.         
      1. Copper(ii)carbonate
      2. Carbon(iv) oxide
   2. Cu²⁺ + CO₃^2-_(aq) → CuCO_3(aq)
   3.        
      1. [Cu(NH₃)₄]^2-
      2.        
         1. Bubbling/ Effervesence
         2. The reaction of H₂SO₄ with CaCO₃ would take place for a short time then stop. This is due to fromation of insoluble CaSO₄
         3. To absorb the traces of HCl_(g)
         4. Ca(OH)_2(aq) forms white ppt while NaOH does not.
5.         
   1. Molar enthalpy of combustion is the amount of heat per 1 mole of a substance undergoing complete combustion.
   2.             
      1. ΔH₂= Molar enthalpy of combustion of carbon
      2.    
         
      3.      
         
         -103.7 + x = 4(-285.8)+3(-393.5)
         x= -11432 - 1180.5= 2323.7
         x= -2220kg/mol
      4.       
         
         5(C-H)=5(-414)=2070
         (C-C)=-1(-346)=346
         (C-O)=1(-360)=360
         =-2776
         -3239-(-2776)
         =-463kj/mol
6.              
   1.          
      1.             
         • The experiment should be carried in a fume chamber or an open place.
         • It should be done ina  dry condition
           
           
      2. 16HCl_(aq)+2KMnO_4(s) → 5Cl_(g) + 2MnCl_(aq) + 8H₂O_(l) + 2KCl_(aq)
      3. Manganese(iv) oxide
      4. To produce Cl₂ gas to force air out which could otherwise react with aluminium to form aluminium oxide, hindering the reaction. 
      5. 2Al_(g) + 3Cl_2(g) → 2AlCl_3(s)
      6. Moist calcium hydroxide - ammonia is highly soluble in water
   2.             
      1. Method of collecting the gas- Ammonia is less dense than air
      2. Calcium oxide(quick lime)
      3. Ca(OH)_2(s) + 2NH4Cl_(s) → CaCl_2(s)+2H₂O_(l) + 2NH_3(g)
      4. Ammonia turns moist red litmus paper blue
7.             
   1.              
      1. A-Ethene
      2. B- Ethane
      3. F- Carbon(iv) oxide
      4. G- hydrogen
   2.          
      1. CH₂=CH₂ → CH₃CH_3(g)
      2. 2C₂H₆+5O₂→ 4CO_2(g) + 6H₂O_(l) 
      3. 2Na_(s) +2H₂O_(l) → 2NaOH_(aq) +H_2(g)
   3. CH₂CH₂
      2c 2 x 12=24
      4H  4 x 1=4
      b=28
      28n=42000
      n=42000.28
      =1500 molecules
   4.              
      1. High temperature
      2. Platinum