Chemistry P1 Questions and Answers - Form 3 Term 3 Opener Exams 2022

INSTRUCTIONS TO CANDIDATES

1. Write your name and admission number in the spaces provided above.
2. Sign and write the date of examination in the spaces provided.
3. ANSWER ALL QUESTIONS IN THE SPACES PROVIDED.
4. All working must be clearly shown where necessary.
5. Mathematical tables or silent electronic calculators may be used.

QUESTIONS

1. Define the following terms (3mks)
   1. Isotopes
   2. Mass number
   3. Isomers
2.                      
   1. Give a reason why ammonia gas is highly soluble in water. (1mk)
   2. The structure of ammonium ion is shown below
      Name the type of bond represented in the diagram by N H……………………… (1mk)
3. Both diamond and graphite have giant atomic structures. Explain why diamond is hard while graphite is soft. (2mks)
4. Using dot (.) and crosses(x) to represent electrons, show bonding in the compounds formed when the following elements reacts. (C-=6, Na=11, F=9)
   1. Sodium and fluorine (1mk)
   2. Carbon and fluorine (1mk)
5. The table below gives information about the major components of crude oil. Study it and answer the questions that follow.
   

   Components	Boiling point oC
   Gases	Below 40
   Petrol	40-175
   Kerosene	175-250
   Diesel oil	250-350
   Lubricating oil	350-400
   Bitumen	Above 400

   1. Which of the compounds of crude oil has molecules with the highest number of carbon atoms? Explain (1mk)
   2. Name the process you would use to separate a mixture of diesel and petrol (1mk)
   3. What condition could cause a poisonous gas to be formed when Kerosene is burnt (1mk)
6. The set up below was used to prepare nitric (V) acid
   
   
   1. Give the name of liquid T(1mk)
      T……………………………………………………………………………………… ..(1mk)
   2. Write the equation for the reaction which took place in the reaction flask (1mk)
   3. Explain why nitric acid is stored in a dark bottle (1mk)
7. The table below gives information on four elements represented by K L M & N. Study it and answer the questions that follow. The letters do not represent the actual symbols of the elements.
   

   Elements	Electron arrangement	Atomic radius	Ionic radius
   K	2, 8 2	0.136	0.065
   L	2, 8, 7	0.099	0.181
   M	2, 8, 8, 1	0.203	0.133
   N	2, 8, 8, 2	0.174	0.099

   1. Which two elements have similar chemical properties? Explain (2mks)
8. A certain carbonate XCO₃ , reacts with dilute hydrochloric acid according to the equation
   XCO₃(s) +2HCl (aq) →  XCl₂ (aq) + CO₂ (g) + H₂O (l)
   If 4g of the carbonate reacts completely with 40cm³ of 2M hydrochloric acid, calculate the relative atomic mass of X.
   (C=12.0 ,O=16.0, Cl=35.5). (3 Marks)
9. Give two uses of ethene gas (2 Marks)
10.                      
    1. What is meant by allotropy? (1 Mark)
    2. The diagram below shows the structure of one of the allotropes of carbon.
       
       
       1. Identify the allotrope ( 1 Mark)
       2. State one property of the above allotrope and explain how it is related to its structure. (2 Marks)
       3. 60cm³ of oxygen gas diffused through a porous hole in 50seconds. How long will it take 80cm³ of sulphur(iv)oxide to diffuse through the same hole under the same conditions (S=32.0 , O=16). (3 Marks)
11. The ionisation energies for three elements X,Y, and Z are shown in the table below:
    

    Element	X	Y	Z
    Ionisation energy (KJ/mole)	419	318	394

    1. What is meant by ionisation energy? (1 Mark)
    2. Which element is the strongest reducing agent? Give a reason. (2 Marks)
12. In the figure below:
    
    
    1. Name the parts labeled F, G, and H. (1 ½mks)
       F……………………………………………………………………………………………....
       G……………………………………………………………………………………………....
       H……………………………………………………………………………………………....
    2. Describe an experiment that would confirm that region labeled G is unsuitable for heating (1½mks)
13. The diagram below is a set up used to investigate the effect of heat on hydrated copper(II) sulphate. Study the diagram and answer the questions that follow.
    copper (II) sulphate crystals
    
    
    1. Why is boiling tube slanted as shown? (1mk)
    2. What is observed in the boiling tube. (1mk)
    3. Identify liquid G. (1mk)
14. The electronic arrangement of two stable ions Q²⁺ and P^2- are 2.8.8 and 2.8.8 respectively.
    1. Write the electron arrangement of atoms Q and P. (1mks)
       Q………………………………………………………………………………………....…
       P………………………………………………………………………………………....…
    2. What is the most likely structure of an oxide element P? (1mk)
15. The set up below was used by a student. Filter paper soaked in purple litmus solution was placed in the middle of the combustion tube.
    
    
    1. What is the main aim of the experiment. (1mk)
    2. State the first observation likely to have been made in the tube. Explain the observation. (2mks)
16. The empirical formula of a compound is CH2 and it has a molecular mass of 42.
    1. What is the molecular formula of this compound? (1mk)
    2. Write the general formula of the homologous series to which the compound belongs. (1mk)
    3. Draw the structural formula of the third member of this series and give its IUPAC name. (1mk)
17. 3.22g of hydrated sodium sulphate, Na2SO4 X H2O were heated to a constant mass of 1.42 g. determine the value of X in the formula ( Na=23.0, S = 32.0, O = 16, H = 1) (3mks)
18. Complete the following reactions. (2mks)
    1. C₂H₂  → 1 mole of HCl(s)
                                  1 mole Cl₂
    2. CH₃CH₃              U.V light
19. A white solid K was heated. It produced a brown gas A and another gas B which relights a glowing splint. The residue left was yellow even after cooling.
    1. Identify gases A and B (1mks)
    2. Write a balanced chemical equation for the decomposition of solid K. (1mk)
20. An atom X contains 90% of ¹⁶₈X isotope and 10% of ¹⁸₈Xisotope. Calculate the relative atomic mass of X. (2mks)
21. Explain why aluminium articles are not easily corroded. (1mk)
22. Dry chlorine gas was passed through two pieces of coloured cotton cloth as shown.
    
    
    1. State what is observed in each experiment. (2mks)
       Experiment 1
       Experiment 2
    2. Explain your observation using an equation for experiment 2 (1mk)
23. When burning magnesium ribbon is put into a gas jar of carbon (IV) oxide gas, it continues to burn leaving behind white solid powder and black solid specks as residue write chemical equation for the reaction that produces.
    1. The white solid powder. (1mk)
    2. Black solid specks. (1mk)
24. Describe how you would obtain pure solid samples of each of the following components of a solid mixture containing ; Lead (II) chloride, Sodium carbonate and calcium sulphate. (3mks)
25.                          
    1. State Boyle’s gas Law. (1mk)
    2. A fixed mass of a gas has a volume of 250cm³ at 27ºC and 750mmHg pressure. Calculate the gas volume that the gas would occupy at 41ºC and 750mmHg pressure. (0º = 273k) (2mks)
26. The diagram below shows a sample of ammonium chloride being heated in a dry boiling tube containing a plug of cotton and dump red litmus paper
    
    State and explain what would be observed on the red litmus paper. (2mks)
27.                      
    1. The following diagram represents a set-up used to investigate conditions necessary fro rusting of iron.
       
       After several days it was found that the nails did not rust. Identify solid P. (1mk)
28.                          
    1. Write a chemical equation for the combustion of laboratory gas , when the Bunsen burner produces a non-luminous flame. (1mk)
    2. Describe two observable characteristics of aluminous flame. (1mk)
29. Name the following compounds (1 mark)
    1. CH₃CH=CHCH₃
    2. CH₃-CH₂-CH-CH₂CH₂CH₃ (1 mark)
                         CH₂CH₃
30. The diagram below represents aset up that can be used to react Lithium with water to produce gas X which is then reacted with copper II oxide.
    
    
    1. Write an equation for the reaction between gas X and CuO (1mark)
    2. Give the observation made in the apparatus (1 mark)
    3. Why is it necessary to burn excess gas at the end of the jet (1 mark)
31. Solution R,S and T have PH values shown in the table below:
    

    Solution	pH value
    R	1.0
    S	6.5
    T	8.0

    1. What do you deduce about the nature of solution R? (1 mark)
    2. Which solution would react most vigorously with sodium hydrogen carbonate. (1 mark)
    3. Which solution is likely to be ammonia solution? (1 mark)

MARKING SCHEME

1.    
   1. Atoms of the same element with same atomic number but different mass
      no.s/neutrons
   2. Total sum of protons and neutrons
   3. Compounds with the same molecular formula but different structural formula
2.    
   1. Both ammonia and water are polar molecules and hydrogen bonds are formed.
   2. Co-ordinate bond/dative bond.
3. In diamond all the bonds are strong covalent bonds while in graphite structure has layers that are held together by weak vander waals forces that are easily broken
4.    
   1.    
      
   2.   
      
5.    
   1. Bitumen, last to be collected has the highest boiling point.
   2. Fractional distillation
   3. Limited supply of oxygen
6.    
   1. Conc. Sulphuric(VI) acid reject if concentrated missing
   2. H₂SO₄ (l) + NaNO_3(s) NaHSO_4(aq) + HNO_3(g)
   3. Prevent decomposition of nitric acid by light
7. K and N; same group/same valence electrons/loose two electrons 
8. No. Of moles of HCl in 40cm³ of 2M HCl
   Moles of HCl in 40cm³ + 2M HCl
   =40 x 2= 0.08 moles
      1000
   XCO₃ : HCl
   1 : 2
   Moles of XCO₃ =0.08 x 1= 0.04 moles
                                   2
   0.04 moles → 4g
   1 mole → ?
   1 x 4= 100g
   0.04
   XCO₃ = 100
   X = 100 - [12 + (16 x 3)] = 40g
9.    
   1. Artificial ripening of fruits
   2. Manufacture of polyethene
10.    
    1. allotropy is the existence of an element in more than one form without change of state
    2.       
       1. graphite
       2.    
          • it is a lubricant because layers slide over each other
          • a good conductor of both heat and electricity because it has delocalised/mobile electrons
       3. RO₂ = √MMSO₂ 
          RO₂        MMO₂
          Rate of O₂ = 60/50 = 12cm³/s
           1.2  = √64
          RO₂       32
           1.2 = 1.414
          RO₂
          = 0.8486
          0.8486 = ⁸⁰/_t 
          t = 80/0.8486
          = 94.27 sec.
11.    
    1. It is the minimum energy required to remove an electron from an atom in gaseous state
    2. Y. It has the lowest ionization energy hence requires the least amount of energy to give out its electron
12.    
    1. F – pale blue zone
       G – almost colourless zone
       H – chimney ( ½mk each)
    2. Slip a piece of manila paper /wooden splint into region and quickly remove before it catches fire. The inner part remains unburnt// not charred ( 1½mks)
    3. Hold a match stick on a pin and let the head rest on the chimney when the chimney is lit the head of the match stick in the zone does not light.
13.    
    1. Prevent water formed to run back to hot part which could crack
    2. Blue solid turns white //crystals form powder //colourless drops of liquid on cooler parts
    3. G is water 
14.    
    1. Q – 2.8.82 (1mk) P – 2. 8.6 (1mk)
    2. oxide of P has simple molecular structure (1mk)
15.    
    1. Compare rate of diffusion of gases
    2. Litmus turns blue NH₃ diffuses faster since it is lighter ( 2mks)
16.    
    1. (CH₂)n = 42
       (12 + 2)n = 42
       14n = 42
       n = 3 √ ½
       Mf = 3(CH₂) C₃H₆ √ ½
    2. CnH₂n √ 1
    3. 
       
       But-2-ene
17. Cpd - 3.22g mass of NaSO₄ = 1.42g
    Mass of H₂O = 3.22 – 1.42 = 1.8g √ ½
    Na₂SO₄ H₂O
    Mass 1.42 1.8
    Moles 1.42 = 0.01 √ ½ 1.8 √ ½ = 0.1
               142                    18
    Mole ratio 0.01√ ½ 0.1
                     0.01       0.1
    1:10
    X = 10 √ ½
18.    
    1. CH₃CH₂OH   Conc. H₂SO₄ 170ºC  CH₂CHC₁ 
    2. CH₃CH₃ 1 mole Cl_2(g) U.V light  CH₃CH₂Cl(g) + HCl(g)
19.    
    1. A – Nitrogen (IV) oxide √ 1/ NO₂(g)
       B – Oxygen/ O2(g) √ 1
    2. 2Pb(NO₃)_2(s) 2PbO_(s) + 4NO_2(g) + O_2(g) √ 1
20. (⁹⁰/₁₀₀ x 16) + (¹⁰/₁₀₀ x 18) √ 1
    = 14.4 + 1.8 = 16.2 √ 1
21. Aluminium reacts with oxygen to from aluminium oxide which coats the surface of he article and prevents further reaction with air and water. √ 1
22.    
    1. Exp. 1 – No change on the dry cloth because no formation of hypoochlorous acid responsible for bleaching.
       Exp. 2- The wet cloth turned white due to bleaching as chlorine dissolves in water in the wet cloth to form hypochlorous
    2. Cl_2(g) + H₂O(l) HCl_(aq) + HOCl_(aq)
    3. Dye + HOCl_(aq) {Dye +[O] } + HCl √1
23.    
    1. O_2(g) + 2Mg_(s) 2MgO_(s) √ (1mk)
    2. 2Mg + CO_2(g) 2MgO(s)+ C(S) √ (1mk)
24.      
    • Mix With Cold Water, Sodium Carbonate Dissolves√ (½mk)
    • Filter off Lead (II) Chloride And Calcium sulphate as residue √ (½mk)
    • Evaporate the filtrate to obtain sodium chloride
    • Mix the residue with hot water to dissolve Lead (II) chloride√ (½mk)
    • Filter off Calcium sulphate as a residue dry over dessicator
    • Cool the filtrate to precipitate Lead (II) chloride √ (½mk)
      Filter off residue as Lead (II chloride and dry √ (½mk)
25. The volume of a given mass of a gas at constant temeprature is inversely proportional to its pressure√ (1mk)
26. Red litmus paper turns blue since ammonium chloride decomposes to form ammonia and hydrogen chloride gas ammonia diffuses faster
27. Anhydrous Calcium Chloride
28.    
    1. Either
       CH_4(g) + O_2(g) CO_2(s) + 2H₂O_(g)
       2C₂H_6(g) + 7O_2(g) 4CO_2(g) + 6H₂O_(l)
       C₃H_8(g) + 5O_2(g) 3CO_2(g) + 4H₂O_(l)
       2C₄H_10(g) + 13O_2(g) 8CO_2(g) + 10H₂O_(l)
    2. Yellow √(½mk) // sooty
       Large, unsteady, √(½mk)
29.    
    1. But-2-ene✔1
    2. 3 –ethylhexane✔1
30.    
    1. H_2(g) + CuO(s) Cu(s) + H₂O(l)
    2. lead(ii)oxide Changes colour from orange to grey lead
    3. to prevent an explosion when it mixes with air. ✔1
31.      
    1. it is strongly acidic✔1
    2. R✔1
    3. T✔1