Form 4 Chemistry Paper 3 Endterm 1 Confidential

Get the Answers here Form 4 End Term 1 Exams 2023 Questions and Answers

1.         You are provided with:

            – 0.1m sodium hydroxide solution F

            – Solution G made by dissolving 9.0g of dibasic acid H₂MO₄ in 250cm³ of distilled water

You are required to:

• Dilute solution G
• Standardize the diluted solution H using the sodium hydroxide solution F
• Determine the mass of M in the formula H₂MO₄

Procedure 1

Using a measuring cylinder measure 20cm³ of solution G and transfer it into a beaker.

Measure 80cm³ of distilled water and add it to the 20cm³ of solution G in the beaker.  Label this as solution H.

Procedure II

Place solution H in a burette.  Pipette 25cm³ of solution F into 250cm³ conical flask.  Add 2 – 3 drops of phenolphthalein indicator and Titrate with solution H.  Record your results in table 1.  Repeat the titration two more times and complete the table.

a)  Table 1

	1	II	III
Final burette reading (cm3)
Initial burette reading (cm3)
Volume of solution H used (cm3)

                                                                                                                                    ( 4 marks)

b)  Calculate the average volume of solution H used.                                                ( 1 mark)

• Determine the number of moles of:-

I           Sodium hydroxide in Solution F in 25cm³                                                     ( 1 mark)

II         Acid in solution H in the average volume used.                                            ( 1 marks)

III        acid in 100cm³ of solution H.                                                                         ( 1 marks)

IV        acid in 20cm³ of solution G.                                                                           ( 1 mark)

V         acid in 250cm³ of solution G                                                                          ( 2 marks)

• Calculate the:

I           Molar mass of acid H₂MO₄                                                                            ( 2 marks)

II         Mass of  M in the formula H₂MO₄ given that H = 1, O=16.                          ( 1 marks)

2.         You are provided with:

            – 0.15M ethan-1,2-dioc acid (oxalic), solution M

            – 0.02M acidified potassium manganate (VII) solution N

You are required to determine the rate of reaction between acidified potassium manganate (VII) and ethan – 1,2 – dioc (oxalic) acid at different  temperatures.

Procedure

1. Place 5cm³ of solution N in a boiling tube
2. Place another 5cm³ of solution M in another boiling tube.
3. Heat solution N on a Bunsen burner flame to 80⁰C.  Allow it to cool to 70⁰C.
4. Add all solution M into solution N and at the same time start the stop watch
5. Stir the mixture and record in table II the time taken for purple colour to disappear.  At the same time record the temperature.
6. Using clean boiling tubes repeat the procedure while allowing solution N to cool to 60⁰, 50⁰C and 45⁰C in each case to complete table II below.

1. Table II

Temperature before mixing oC	70	60	50	45
Temperature at which purple colour disappear 0C
Time taken for purple colour to disappear
1/time sec

                                                                                                                                    ( 4 marks)

b)  On the grid of graph paper provided plot ¹/_time ( y-axis) against temperature at which the purple colour disappears.                                                                                           ( 3 marks)

b)  From your graph;

            I.          determine the time taken for purple colour to disappear at 47.5⁰C.               ( 1 marks)

II         State the relationship between rate of reaction and the temperature at which purple colour disappears.                                                                                          ( 1 mark)

………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………………

3.  a)You are provided with substance P for this question. Transfer the substance into a clean boiling tube. Add about 10cm³ of distilled water and stir. Pour the mixture into four clean test tubes of about 2cm³ each.

Observations	Inferences
1mk	1mk

1. To the first portion of the solution, add sodium hydroxide solution dropwise until in excess.

Observations	Inferences
1mk	1mk

1. Dip a clean stirring rod/glass rod/nichrome wire into the second portion and then place into the side of a blue bunsen flame.        

Observations	Inferences
½ mk	1mk

1. To the third portion, add 2-3 drops of barium nitrate solution followed by excess hydrochloric acid.

Observations	Inferences
1mk	½ mk

1. To the fourth portion, add 2-3 drops of acidified potassium manganate (VII)

Observations	Inferences
½ mk	1mk

• You are provided with solid K.  Carry out the tests below.  Write your observations and inferences in the spaces provided.
•  Using a clean metallic spatula, heat about one third of solid K in a Bunsen burner flame.

Observations	Inferences
(1mk)	( 1mark)

1. Dissolve the remaining portion of solid K into about 10cm³ of distilled water and divide the solution into 4 portions.

To the first portion, add two drops of acidified potassium permanganate solution.

Observations	Inferences
(1mark)	( 1 mark)

1. To the second portion, add two drops of bromine water.

Observations	Inferences
(1mark)	(1mark)

1. Determine the pH of the third portion using universal indicator paper.

Observations	Inferences
( ½ mk)	( ½ mk)

• To the fourth portion, add a small amount of solid sodium hydrogen carbonate.

Observations	Inferences
(1mark)	(1mark)

	END