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

INSTRUCTIONS TO THE CANDIDATES:-

• Answer all the questions in the spaces provided.
• Mathematical tables and electronic used calculators may be
• All working MUST be clearly shown where necessary.

1. The figure below represents a section of the periodic table. Study it and answer questions (a) to (h). Note that the letters do not represent the actual symbols of the elements.
   
   1. Consider elements D. H and I
      1. Give the chemical family of these elements. (1 mk)
      2. How do their ionic size compare. (1mk)
      3. Compare and explain the reactivity of the three elements. (2mks)
   2. Write the electronic configuration of;
      1. Element H (1mk)
      2. The ion of element G. (1mk)
   3. A molecule of one of the elements is shown below. (2mks)
      
      1. Identify this element from the section of the periodic table and give its actual symbol and name. (2mks)
      2. Explain why this element has a higher boiling point compared to that of oxygen. (2mks)
      3. Write an equation to show the reaction between the element named above with oxygen. (1mk)
      4. Predict the pH of the oxide of the above element when in water. Explain. (2mks)
2. The flow chart below shows some reactions starting with copper (II) nitrate. Study it and answer questions that follow.
   
   1. State the condition necessary in step 1. (1mk)
   2. Identify: (4mks)
      1. Reagent M …………………………………………………………………………………….
      2. Gas S ………………………………………………………………………………………..
      3. Acidic products T………………………………………………………………………………
      4. V…………………………………………………………………………………………………
   3. Write the formula of the complex ion formed in step 3. (1mk)
   4. Write the equations for the reaction in (2 marks)
      1. Step 1
      2. Step 2
3.  
   1. The diagram below shows a set up that was used to prepare oxygen gas and passing it over a burning candle. The experiment was allowed to run for some time.
      
      1. Name liquid X (1mk)
      2. Suggest the pH of the solution in conical flask K. Explain (2mks)
      3. Write an equation for the reaction taking place in the conical flask M. (1mk)
   2. State and explain the two observations made when hydrogen sulphide is bubbled into the solution containing iron (III) chloride. (2mks)
   3.  
      1. Describe a simple chemical test that can be used to distinguish between carbon (IV) oxide and carbon (II) oxide gases. (3mks)
      2. Give one use of carbon (II) oxide. (1mk)
   4. A form two student inverted a gas jar full of carbon (IV) oxide over water and sodium hydroxide solution as shown below.
      
      Explain the observations made. (2mks)
4.  
   1. Name the two crystalline forms of sulphur (1 Mark)
   2. The scheme below represents the steps followed in the contact process. Study it and answer the questions that follow:-
      
      
      1. Name one impurity removed by the purifier. (1 mark)
      2. Why is it necessary to remove impurities? (1 mark)
      3. Write down the equation of the reaction taking place in the converter (1 mark)
      4. Name the two catalysts that can be used in the converter (2 marks)
      5. What is the function of heat exchanger? (1 mark)
      6. Sulphuric (VI) Oxide is not dissolved directly into water?  Explain.
      7.  
         1. Name the main pollutant in the contact process. (1 mark)
         2. How can the pollution in (g) (I) above be controlled? (1 mark)
      8. Give one use of sulphuric (VI) acid (1 mark)
5. The flow chart below shows industrial manufacture of sodium carbonate. Study it and answer the questions that follow.
   
   1. Name substances A, B, C and D. (4mks)
   2. Write equation for the reactions taking place in chamber 3 and 5. (2mks)
   3. Name the physical process in chamber 4 and 5. (2mks)
   4. Name one source of cheap carbon (IV) oxide for Solvay process. (1mk)
6.  
   1. A student set up the apparatus as shown in the diagram below to prepare and collect dry ammonia gas.
      
      1. Identify three mistakes in the set up and give a reason why each is mistake. (3mks)
      2. Name a suitable drying agent for ammonia. (1mk)
      3. Write an equation for the reaction that occurred when a mixture of ammonium chloride and calcium hydroxide was heated. (1mk)
      4. Describe one chemical test for ammonia gas. (1mk)
   2. Ammonia gas is used to manufacture nitric (V) acid as shown below.
      
      1. This process requires the use of a catalyst. In which unit is the catalyst used? (1mk)
      2. Identify compound X and Y. (2mks)
      3. Ammonia reacts with nitric (v) acid to form ammonium nitrate fertilizer. Calculate the percentage composition of nitrogen in ammonium nitrate. (N = 14, O = 16, H = 1) (3 marks)
7.  
   1. State Graham’s Law. (2mks)
   2. The table below shows the relationship between the pressure and volume of a fixed mass of ozone gas.
      

      Pressure (K pa)	1	4	8	16	20	160
      Volume (cm3)	140	40	20	10	8	1
      Inverse of volume 1/v (cm−3)

      1. Complete the table by filling the inverse of volume. (3mks)
      2. Draw a graph of pressure against the reciprocal (inverse) of volume. (4mks)
   3. Using the graph, determine the volume of ozone if pressure is 12Kpa. (3mks)

MARKING SCHEME

1.  
   1.  
      1. Halogens
      2. Ionic radius increases from D to I this is due to increase in number of energy.
      3. Reactivity reduces from D to I due to increase in atomic radius down the group which leads to a decrease in the strength of nuclear force of attraction.
   2.  
      1. 2.8.7
      2. 2.8
   3.  
      1. F – S – Sulphur
      2. A molecule of sulphur is made of packed ring of 8 atoms joined by strong covalent bonds while a molecule of oxygen has weak van der wall forces hence higher B.P of sulphur than oxygen.
      3. S_(s) + O_2(g) →SO_2(g)
      4. Below 7 because SO₂ dissolves in water to form acidic solution of sulphurous acid.
2.  
   1. Heating
   2.  
      • M – sodium carbonate/ potassium carbonate
      • S – oxygen
      • T – nitric (v) acid
      • V – nitric (III) acid
   3. [Cu(NH₃)₄]²⁺
   4.  
      1. 2Cu(NO₃)_2(s)→ 2CuO_(s) + 4NO_2(g) + O₂
      2. NO_2(g) + H₂O_(l) →HNO_2(aq) + HNO_3(aq)
3.  
   1.  
      1. Water
      2. Any pH between 4 - 7 – due to presence of carbonic acid
      3. 2Na₂O_2(aq) + 2H₂O_(l) → 2NaOH_(aq) + O_2(g)
   2. Brown solution change to pale green solution. This is due to F³⁺ reduced to Fe²⁺ by H₂S
   3.  
      1. When CO₂ is bubbled in lime water white precipitate is formed while NO₂ white precipitate formed with CO.
      2. Extraction of metals, used as fuel
   4. CO₂ is highly soluble in sodium hydroxide to form Na₂CO₃ while is slightly soluble in water.
4.  
   1.  
      • Rhombic sulphur (½ mk)
      • Monoclinic sulphur (½ mk)
   2.  
      1. Dust or Arsenic compounds (½ mk)
      2. Avoid poisoning of the catalyst (Avoid destruction of catalytic properties by impurities
      3. 25O_2(g) + O_2(g) → 2SO_3(g)
      4. Vanadinim (V) Oxide ( ½ mk)
      5.  
         • Heat incoming air (SO₂ & Air)
         • Cools the SO₃
      6. The reaction between SO₂ and water is highly exothermic which makes the solution boil to form a mist of dilute sulphuric (VI) acid which pollutes the environment
      7.  
         1. SO₂
         2.  
            • Un reacted SO₂ is recycled
            • Absorbed by Ca(OH)₂ in tall chimneys
            • Passed over hot carbon (IV) Oxide and sulphur which is recycled and Carbon (IV) Oxide released to the environment
      8. Manufacture of fertilizers
5.  
   1.  
      • Ammoniacal brine/ammoniate brine
      • Sodium hydrogen carbonate/NaHCO₃
      • Ammonium chloride/NH₄Cl
      • Calcium chloride/CaCl₂
   2. 2NH₄Cl_(aq) + Ca(OH)_2(aq) → CaCl_2(aq) +2H₂O_(l) + 2NH_3(g)
      NaHCO_3(s)  Na₂CO_3(s) + H₂O_(l) + CO_2(g)
   3.  
      • Filtration
      • Decomposition
   4. Limestone/Calcium carbonate
6.  
   1.  
      1.  
         • Wrong method of collection.√1/2 (3mks)
         • ammonia is less denser than air.√1/2\
         • Flask should be slanting downwards left to right .√1/2
         • Water produced may run back & break the flask .√1/2
         • Moist reactants should not be used .√1/2
         • ammonia gas dissolves in water .√1/2
      2. Anhydrous calcium oxide
      3. 2NH₄Cl_(s) + Ca(OH)_2(s)→ 2NH_3(g) + 2H₂O_(l) + CaCl_2(s)
      4. Deep a glass rod in conc. HCl and bring it into contact with ammonia in a test tube. White fumes formed.
   2.  
      1. Unit 1
      2. X – nitrogen (II) oxide (NO)
         Y – nitrogen (IV) oxide (NO2)
      3. NH₄NO₃
         N = 28
         H = 4
         O = ⁴⁸/₈₀   ²⁸/₈₀ x 100
            = 35.0%
7.  
   1. The volume of a fixed mass of a gas is inversely proportional to its pressure at constant temperature. (1mk)
   2.  
      1.  
         

         Pressure (K pa)	1	4	8	16	20	160
         Volume (cm3)	140	40	20	10	8	1
         Inverse of volume 1/v (cm−3)	0.006	0.025	0.05	0.1	0.125	1.000

         (3mks)
      2. axes- ½mk, scale- ½mk, line-1mk, plotting-1mk
   3.  
      1. Reading from the graph (student graph)(1mk)
      2. evaluation on the reciprocal of volume.(1mk)