Chemistry P3 Questions and Answers with Confidential - Form 3 Term 3 Opener Exams 2022

INSTRUCTIONS:

1. Write your name, admission number and class
2. Answer all the questions in the spaces provided
3. Spend the first 15 minutes of the 2 ¼ hours to read the questions paper and ensure you have all the chemicals and apparatus that you may need.
4. All working must be clearly be shown where necessary
5. Mathematical tables and silent calculators may be used
6. Answer all the questions in English language

QUESTIONS

1. You are provided with the following reagents.
   • 60cm3 of solution M which is IM hydrochloric acid
   • About 80cm3 sodium hydroxide solution K made by dissolving 5.6g of sodium hydroxide into 200cm3 of distilled water and diluting it to make 1dm3 of the solution K.
   • Anhydrous sodium carbonate solid X of unknown mass.
   • Methyl orange indicator
     You are required to determine the mass of solid X in grams using the procedure below.
     Procedure:
     Place all the solid X into a 250cm3 volumetric flask provided. Use your burette to transfer 50cm3 of solution M into the 250cm3 volumetric flask containing solid X and allow the reaction to take place until the effervescence stops. Add the distilled water using the wash bottle to fill to the mark and label the resulting solution N. Pipette 25.0cm3 of solution K into a 250.0cm3 conical flask and add 2 to 3 drops of methyl orange indicator. Swirl the contents. Rinse your burette with distilled water and fill it with solution N.
     Titrate solution K with N until a colour change just occurs. Repeat the titrations to complete the table below.
     

     	I	II	III
     Final burette  reading(cm3)
     Initial burette reading(cm3)
     Volume  of  solution N used(cm3)

     (3mks)
     1. Calculate the average volume of solution N used (1mk)
     2. Calculate the number of moles of:
        1. Solution K that reacted in the experiment above (Na=23, H=1, O=16) (3mks)
        2. Solution N that reacted in the above experiment (2mks)
        3. Solution N in 250cm³ (2mk)
        4. 50cm3 of solution M before reaction with solid X (2mks)
     3. Hence or otherwise calculate the number of moles of:
        1. Hydrochloric acid which reacted with solid X (2mks)
        2. Solid X which reacted in the experiment (2mks)
     4. Calculate the mass of solid X which was reacted above. (3mks) (Na=23, C=12, O=16)
2. Carry out the tests on the substances given and record your observations and inferences in the space provided.
   1.                        
      1. Put half of solid A in a boiling tube. Add about 3cm3 of distilled water shake and retain the solution
         

         Observation	Inferences
         (1/2 mk)	(1/2 mk)

      2. To the solution above, add a few drops of ammonia solution then add in excess.
         

         Observation	Inferences
         (1mk)	(1mk)

      3. Add the remaining half of solid A in a test tube and add about 3cm3 of water and dissolve. Dip a glass rod in the solution and burn the end dipped on a non-luminous flame.
         

         Observation	Inferences
         (1/2 mk)	(1/2 mk)

   2.                    
      1. Put ½ of solid B in a test tube and add about 1cm3 of distilled water.
         

         Observation	Inferences
         (1mk)	(1mk)

      2. Put the remaining solid in a test tube and add about 1cm3 of dilute hydrochloric acid
         

         Observation	Inferences
         (1mk)	(1mk)

   3.                     
      1. Put ½ of solid C in a test tube, heat gently then strongly observing the colour changes in the solid when heating and after cooling. Test any gas produced with wet litmus paper and a glowing splint.
         

         Observation	Inferences
         (3mks)	(1mk)

      2. Put the remaining solid C in a test tube and add about 2cm³ of distilled water, shake well add ammonia solution dropwise then in excess.
         

         Observation	Inferences
         (1mk)	(1mk)

   4. Divide solution F into 3 portions.
      1. Test the pH of the first portion with universal indicator
         

         Observation	Inferences
         (1mk)	(1mk)

      2. In the second portion drop a piece of magnesium ribbon and test for any gas produced with burning splint.
         

         Observation	Inferences
         (1mk)	(1mk)

      3. To the third portion add a ¼ spatula of sodium hydrogen carbonate.
         

         Observation	Inferences
         (1mk)	(1mk)

CONFIDENTIAL

1. About 80cm³ of solution K
2. About 60cm³ of solution M
3. Solid X
4. Burette (50.0cm³)
5. Pipette (25.0cm³) and a pipette filler
6. 250cm³ volumetric flask
7. At least two conical flasks
8. 1 label
9. Tile, funnel, stand clamp and boss
10. Distilled water
11. About 8 test tubes
12. Metallic spatula
13. Two boiling tubes
14. pH chart
15. 2cm length magnesium ribbon(cleaned)
16. 2 wooden splints
17. ½ spatula of sodium hydrogen carbonate
18. One red and one blue litmus papers
19. Test tube holder
20. ½ spatula of the solids below
    
    1. - Na₂SO₄
    2. -Na₂CO₃
    3. -Zn (NO₃)₂
21. Solution F – 10cm³ 1M HO

Access to:

1. Means of heating
2. Methyl orange indicator
3. 2M ammonia solution
4. 0.5M HCl
5. Universal indicator

NB:

1. Solid X is 1.0g of accurately weighed sodium carbonate
2. Solution M is made by diluting 85cm³ of dilute hydrochloric acid using distilled water to a litre of solution.
3. Solution K is made by dissolving 5.6g of sodium hydroxide pellets to a litre of solution.

MARKING SCHEME

1. Table
   

   Exp No	I	II	III
   Volume of solution N(cm3)	30.7	30.6	30.6

   CT – 1
   D - 1
   A - 1
   
   1. Average volume
      Average at least two litres whose range is not beyond 0.2
   2.    
      1. Molarity of solution K =5.6= 0.14 (1mk)
                                              40
         Moles =V x M=25 x 0.14= 0.0035 (1mk)
                      1000     1000
      2. N is reacting with K
         Hcl_(aq) + NaOH_(aq)→NaCl_(aq) + H₂O (1mk)
         Mole ratio 1:1
         Hence moles of N = 0.0035 moles (1mk)
      3. Solution N in 250cm³
         if 0.0035 moles are in the average volume
         moles in 250 =0.0035 x 250
         AV. Volume (1mk)
      4. Moles = 50 x 1
                       1000
         = 0.05 moles (2mks)
   3.    
      1. Moles in b(iv) above – moles in b(iii) above (1mk)
      2. 2HO_(aq) + Na₂CO_3(aq)→ 2NaCl_(aq) + CO_2(g) + H₂O_(g) (1mk)
         Solution M   Solid X
                  2       :   1
         Moles of solid X = 1 x moles in c(i) above
                                                    2 (1mk)
   4. Moles = Mass
      R.F.M.
      Moles in (ii) above = Mass
      106 (1mk)
      Mass of solid X= 106 x moles in c(ii) above (1mk)
      = Ans (1mk)
2. 1.    
      1.     
         

         Observation	Inference
         Dissolves to form a colourless solution	Soluble salt present or absences of coloured ions Fe2+,Fe3+,Cu2+

      2. Observation	Inference
         No white precipitate is formed	K+ or Na+ present

      3. 
         

         Observation	Inference
         Burns with a yellow flame	Na+ present

   2.    
      1. 
         

         Observation	Inference
         It dissolves to form a clear solution	Soluble salt Absence of Fe2+,Fe3+,Cu2+

      2.   
         

         Observation	Inference
         There is effervescence or bubbling	CO2-3 or SO2-3present, HCO3-

   3.    
      1. 
         

         Observation	Inference
         When hot its yellow in colour When cold it turns white 1mk A glowing splint relights ½mk The blue litmus paper turns red while the red remains red (1mk) Brown gas is produced ½mk	Zn2+ and NO3- IONS PRESENT

      2. 
         

         Observation	Inference
         White precipitate which dissolves in excess	Zn2+ present

   4.    
      1. 
         

         Observation	Inference
         pH range 1-3(only one)	Strongly acidic

      2. 
         

         Observation	Inference
         There is effervescence Gas extinguishes a burning splint with a pop sound	H2 gas present H+ present

      3. 
         

         Observation	Inference
         There is effervescence	Presence of H+ ions