Chemistry Questions and Answers - Form 4 Mid Term 2 2022

QUESTIONS

SECTION A (50MKS)

1.    
   1. Give two reasons why most laboratory apparatus are made of glass. (1 mark)
   2. The diagrams below are some common laboratory apparatus. Name each apparatus and state its use. (2mks)
      
2. Two immiscible liquids P and U were found to have densities 1.65g/cm³ and 0.52g/cm³ respectively. Using the most suitable set of apparatus, describe how one can separate them. (2 marks)
3. When hydrogen chloride gas dissolves in pure ethanoic acid the following equilibrium is established.
   CH₃COOH_(l) + HCl(g) ⇌ CH₃COOH+2(aq) + Cl–(aq)
   
   1. Identify the acid in the forward reaction. (1 mark)
   2. Identify its conjugate base. (1 mark)
4. Metals J, K, L and M and their respective oxides were reacted. Metal M reduced the oxides of K and L. Metal L reduced the oxide of K and metal J reduced the oxide of M.
   
   1. Arrange the metals in order of reactivity starting with the least reactive. (2 marks)
   2. Which of the above metals can be used as a sacrificial metal in electroplating of metal M. (1 mark)
5.    
   1. State two observations made when a small piece of potassium metal is put in a trough full of water (2 marks)
   2. Write a chemical equation for the reaction. (1 mark)
6. The atomic number of element Q is 15 and that of R is 9.
   
   1. Write the electronic arrangement of element Q and R (1 mark)
   2. Using dots (•) and crosses (x) to represent electrons, draw a diagram to show bonding in the compound formed. (2 marks)
   3. Give the chemical family to which element R belongs. (1 mark)
7. Study the table below and answer the questions that follow.
   

   Substance		A	B	C	D	E	F
   Melting point (°C)		801	113 or 119	-39	5	-101	1356
   Boiling  point (°C)		1410	445	457	54	-36	2860
   Electrical conductivity	solid	poor	poor	good	poor	poor	poor
   	liquid	good	poor	good	poor	poor	poor

    Identify with reasons the substances that have
   
   1. a metallic structure (1 mark)
   2. a molecular structure (1 mark)
   3. Substances A and C conduct electric current in liquid state. State how the two substances differ as conductors of electric current. (2 marks)
8. Describe how a sample of calcium carbonate can be prepared in the laboratory starting with calcium oxide. (3 marks)
9. Carbon (II) oxide CO is prepared by passing carbon (IV) oxide over red hot charcoal.
   
   1. Complete the diagram below showing how pure carbon (II) oxide can be collected. (2 marks)
      
   2. Write chemical formulae of two other gases which can be similarly collected. (1mark)
10. Nitric (V) acid may be prepared in the laboratory by the reaction of concentrated sulphuric acid on a suitable nitrate and distilling off nitric (V) acid. This reaction is carried out in an all glass apparatus.
    
    1. Explain why the apparatus consisting of glass is only desirable for this preparation (2 marks)
    2. Pure nitric (V) acid is a colourless liquid but the product in this preparation is pale yellow. Explain. (2 marks)
11. The diagram below represents pipes used in the Frasch pump for the extraction of sulphur.
    
    Which substances pass through the tubes?(3mks)
12. The diagram below shows a set up for large scale manufacture of hydrochloric acid.
    
    
    1. Name substance X (1 mark)
    2. What is the purpose of the glass beads? (1 mark)
    3. Give one use of hydrochloric acid (1 mark)
13. The graph below shows the behaviour of a fixed mass of a gas at constant temperature.
    
    
    1. What is the relationship between the volume and pressure of the gas? (1 mark)
    2. A fixed mass of a gas at 750mmHg pressure and -23ºC temperature occupies a volume of 600cm³ What volume will it occupy at 33ºC and 900mmHg? (2 marks)
14. 10 molecules of an unknown gas have a mass of 1.0667 x 10^-21g. Determine the relative molecular mass of the gas. (L = 6.0 x 10²³) (2 marks)
15. 10cm³ of a gaseous hydrocarbon was mixed with 90cm³ of oxygen and sparked. The resulting volume at r.t.p was 70cm³ which was reduced by 30cm3 on shaking with sodium hydroxide. Find the empirical formula of the hydrocarbon. (3 marks)
16.    
    1. Draw the structural formulae of propane and propan-2-ol (1/2 mark)
       Propane
       Propan-2-ol (1/2 mark)
    2. Give the chemical test for distinguishing propane from propene. (1 mark)
17. Some average bond energies are given below.
    

    Bond	Energy in kJmol-1
    C-C	348
    C_H	414
    Cl-Cl	243
    H-Cl	340
    C-Cl	432

    Calculate the energy change for the reaction below
    C₂H₆ + Cl₂(g) → CH₃CH₂Cl(g) + HCl_g (3 marks)

SECTION B (50MKS)

18. The table below shows the atomic numbers and boiling points of element U, V, W, X and Y (not their actual symbols). Study it and answer the questions that follow.
    

    Element	Atomic number	Boiling point (°C)
    U	3	1330
    V	13	2470
    W	16	445
    X	18	-186
    Y	19	774

    1. Select the elements which belong to the same
       1. Group (1 mark)
       2. Period (1 mark)
    2. Which element :
       1. Is gaseous at room temperature ? Explain (room temperature = 298K) (2 marks)
       2. Does not form an oxide (1 mark)
    3. Write the
       1. Formula of the sulphate of element (1 mark)
       2. Equation for the reaction between Y and W(1 mark)
    4. What type of bond exists in the compound formed between U and W? Give a reason for your answer. (2 marks)
    5. An aqueous sulphate of element V was electrolysed using carbon electrodes. Name the products at the:
       1. Cathode (1 mark)
       2. Anode (1mrk)
19. Study the set up below which was used by Form Four students to prepare a gas in the laboratory.
    
    
    1. Write the equation for the reaction in the flask. (1 mark)
    2. State a chemical test for the gas prepared. (1 mark)
    3. When hydrogen sulphide gas was bubbled into an aqueous solution of iron (II) chloride a yellow precipitate was deposited.
       1. State the other observation that was made. (1 mark)
       2. Write the reaction equation for c (i) above. (1 mark)
    4. When sugar crystals were reacted with concentrated sulphuric (IV) acid, a black substance T was formed which when dried burnt in excess air to form a colourless gas U only. While when concentrated sulphuric (VI) acid is reacted with liquid D at temperature of 170ºC, a colourless gas W is formed this turns brown bromine water to colourless and also turns colour of substance Y from purple to colourless.
       1. Identify substances (5 marks)
       2. Which property of concentrated sulphuric (VI) acid is being demonstrated by formation of a black mass? (1 mark)
20. The flow chart below shows some chemical reactions. Use it to answer the questions that follow.
    
    
    1. Write the name and formula of the organic compounds P, V and W
       1. Name P (½ mark)
          Formula (½ mark)
       2. Name V (½ mark)
          Formula (½ mark)
       3. Name W (½ mark)
          Formula (½ mark)
    2. Write the name of the process that leads to the formation of substance(s) (11/2mks)
    3. Give one necessary condition for the formation of compound P (1/2mark)
    4. If the relative molecular mass of compound U is 84,000 units, determine the value of n.
       (c = 12, O = 1.0) (2 marks)
    5. Write an equation for the reaction leading to the formation of substance S (1 mark)
    6. State and explain the observation made when substance ‘W’ and C₂H₄ are burnt in excess air. (2 marks)
21. In an experiment to determine the molar heat of neutralisation of hydrochloric acid with sodium hydroxide, students of Kima Secondary school reacted 100cm³ of 1M hydrochloric acid with 50cm³ of 2M sodium hydroxide solution. They obtained the following results :
    Initial temperature of acid = 25.0ºC
    Initial temperature of base = 25.0ºC
    Highest temperature reached with the acid - alkali mixture = 34.0ºC
    1. Define the term molar heat of neutralization. (1 mark)
    2. Write an ionic equation for the neutralization reaction between hydrochloric acid and sodium hydroxide. (1 mark)
    3. Calculate:
       1. The amount of heat produced during the reaction. (S.h.c of solution = 4.2kJkg-1k-1) (2 marks)
       2. The molar heat of neutralization of sodium hydroxide. (1 mark)
       3. Explain why molar heat of neutralization of 1M NaOH is higher than that of 1M NH₄OH when reacted with 2M HCl. (2 marks)
    4. Write the thermochemical equation for the reaction involving neutralization of 1M hydrochloric acid with 2M sodium hydroxide. (1mk)
    5. Draw an energy level diagram for the reaction in (d) above. (2 marks
    6. Below are heats of combustion of carbon, hydrogen gas and ethanol.
       • Hc(carbon)H = -393kJ/mol
       • Hc(hydrogen)H = -268kJ/mol
       • Hc(ethanol)H = -1368kJ/mol
         Calculate the heat of formation of ethanol (3 marks)
22.      
    1. Name the chief ore from which iron is extracted. (1 mark)
    2. Name the two impurities found in iron ores. (2 marks)
    3. Iron rusts in the presence of moist air. Give the chemical name of rust. (1 mark)

MARKING SCHEME

1.      
   1. glass does not react with most chemicals
      It is transparent one can see when the reaction is taking place or it is easy to clean
   2. Name: Desicator
      Use : Drying or keeping substance from moisture crystals
      Name: evaporating dish
      Use: evaporating liquids to obtain crystals
2. 
   Working diagram
   • Place the mixture into the separating funnel and let it settle
   • On separating into layers open the tap
   • Allow the first layer to drain the close the tap
3.      
   1. Hydrogen chloride gas donates hydrogen chloride
   2. Level of ionisation / dissociation
4.    
   1. K, L, M, J
   2. J
5.        
   1.      
      • Bursts into lilac flame 
      • Darts on the surface of the water 
      • Produces a hissing sound 
      • Floats 
   2. 2K(s) + 2H₂O(l) → 2KOH(aq) + H_2(g) 
6.      
   1. Q = 2.8.5
      R = 2.7
   2.     
      
   3. Halogens
7.            
   1. C good conductor of electricity in both solid and liquid state due to delocalised electrons
   2. D or E are poor conductor in both solid / liquid state
      Have relatively low Mpt and Bpt due to molecular structure 
   3. A - mobile / free ions
      B - delocalised electrons 
8. Add excess dilute nitric (V) acid to the given calcium oxide.
   Calcium nitrate is formed 
   Add sodium carbonate solution / K₂CO₃ //
   (NH₄)₂CO_3(aq) to the calcium nitrate solution formed, filter obtain CaCO₃ as residue
9.      
   
10.      
    1. Glass apparatus withstand the high temperatures used in this experiment and are corrosion resistant
    2. Nitric (V) acid prepaid has dissolved NO₂
11. 1 - Compressed hot air in 
    2 - Molten froth of sulphur water mixture out
    3 - superheated water-in 
12.              
    1. X - hydrogen gas 
    2. To increase the surface area of absorption of hydrogen chloride gas in water 
    3. Manufacture of dyes, drugs, photographic materials. A commonly laboratory reagent used in schools and in researched institutions
13.      
    1. Volume is inversely proportional to pressure (P  1/V)
    2. P1V1 = P2V2 
         T1         T₂
       P1 = 750mmHg
       V1 = 600cm³
       T1 = 273 - 23 = 250K 
       P₂ = 900mmHg
       V₂ = ?
       V₂ = 750 x 600 x 306 = 612cm³
                   250 x 900
14. 10 molecules = 1.0667 x 10^-21 
    6.0 x 10²³ = ?
    = 6.0 x 10²³ x 1.0667 x 10^-21 
           10
    = 64.002g
15. C_xHy_(g) + O_2(g) → CO_2(g) + H₂O(g)
    10cm³ 90cm³ 30cm³
    Excess volume of = 70 - 30 = 40cm³ 
    oxygen
    volume of O₂ reacted = 90 - 40 = 50cm³
    C_xHy_(g) + 5O_2(g) → 3CO_2(g) + 4H₂O(g) 
    empirical formula = C₃H₈
16.        
    1. 
       
    2. Bubble the two gases separately through acidified potassium manganate (VII) 
       Propene decolourises it but not propane 
       Or Bubble the two gases separately through bromine  (liquid or water) in the dark propene decolourises but not propane 
17. 
    

    Reactants	Products
    C-C = 348 x 1 = 348 C-H = 6 x 414 = 2484 Cl-Cl = 243 x 1 = 243 +3075KJ/mol	C-C= 348 x 1 = 348 C-H = 5 x 414 = 2070 C-Cl = 432 x 1 = 432 -2850KJ/mol

    ΔH = 3075 - 2850
    = + 225KJmol^-1

SECTION B (50MKS)

18.      
    1.      
       1. Same group : U and Y 
       2. Same period: V, W and X 
    2.    
       1. X, Bpt = (-186 + 273) 
          = 87K below room temp. 
       2. X
    3.      
       1. V₃(SO₄)₂
          = V₂(SO₄)₃ 
       2. Y(s) + W₂ → 2Y₂W(s) 
    4. Ionic bond
       U loses electrons the electrons gained by W 
    5.      
       1. Cathode
          Hydrogen gas 
       2. Anode: oxygen gas 
19.        
    1. FeS(s) + 2HCl(aq) → FeCl_2(aq) + H₂S(g)
    2. Blackens wet lead ethanoate powder
       (any other possible test) 
    3.      
       1. A green solution is formed
       2. 2FeCl₃(aq) + H₂S(s) → 2FeCl_2(aq) + 2HCl(aq)
    4.      
       1. T - carbon 
          U - carbon (IV) oxide 
          D - ethanol 
          W - ethene 
          Y - acidified potassium manganate (VII)
       2. Dehydration 
20.      
    1.      
       1. P – ethylethanoate formula
       2. 1, 2, dibromo-ethane
          
       3. ethane
          
    2. reaction process
       V –Addition halogenation
       T - Substitution
       P - Esterification
    3. Concentrated H₂SO₄
    4. 28n = 84000 
       n = 3000 
    5. 2CH₃CH₂OH(l) + 2Na(s) → 2CH₃CH₂ONa(s) + H_2(g)
    6. W burns with a blue flame 
       C₂H₄ burns with a yellow sooty flame 
21.        
    1. The enthalpy change that occurs when one mole of H+ ion react with one mole of OH ion forming one mole of water
    2. H+(aq) + OH–(aq) H₂O(l)
    3.       
       1. The volume of mixture = (100 + 50)cm³
          = 150cm³
          Mass of mixture = 150 
                                      1000
          = 0.15kg
          Average initial temp. = 25 + 25 = 50 = 25ºC
                                                     2         2
          Change in temp.
          = 34 - 25 = 9ºC
          H = MCT
          = 0.15 x 4.2 x 9
          = 5.67KJ
       2. Moles of NaOH
          If 1000cm³ contains 2 moles
          Then 50cm³ contains 50 x 2 = 0.1 moles
                                              1000
          If 0.1 moles evolve 5.67KJ
          Then 1 moles evolve 5.67 = 56.7kJ
                                             0.1
          Hnuet = -56.7kJ/mole
       3. NH₄OH is a weak base that dissociates
          partially while NaOH is a strong base that dissociates completely. Some heat is absorbed before neutralisation takes place for NH₄OH
    4. NaOH(aq) + HCl(aq) → NaCl(aq) + H₂O(l) Hnuet = -56.7KJ/mole
    5.      
       
    6.     
       
22.      
    1. Haemitite Fe₂O₃ or magnetite Fe₃O₄
    2. Silicon (IV) oxide (silica) / Aluminium oxide
    3. Hydrated iron (III) oxide