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Chemistry Paper 3


You are provided with:

Magnesium ribbon, solid A

0.7M hydrochloric acid, solution B.

0.3M sodium hydroxide, solution C.

Distilled water.

You are required to determine the:

i) Temperature change when magnesium ribbon reacts with excess hydrochloric acid.

ii) Number of moles of hydrochloric acid that remain unreacted.

iii) Number of moles of magnesium that reacted.

iv) Molar heat of reaction between magnesium and hydrochloric acid.

Procedure I

Using a burette, measure 50cm3 of solution B and place it in a 100m/s beaker, measure the temperature of solution B and record the value in table 1. Put the magnesium ribbon in 50cm3 of solution B in the beaker and immediately start a stop watch / clock. Stir the mixture continuously with the thermometer making sure that the magnesium ribbon remains inside the solution as it reacts. Measure the temperature after every second and record the values in table I. Continue stirring and measuring the temperature to complete table I.

Keep the resulting solution for use in procedure II

i) Plot a graph of temperature (Y-axis ) against time on the grid provided.

ii) On the graph, show the maximum change in temperature, , and determine its value.

Value of .................................................................................................................................................

Procedure II

Transfer all the solution obtained in procedure I into a 250ml conical flask. Rinse the burette and use it to place 50cm3 of distilled water into the beaker used in procedure I. Transfer all the 50cm3 of water into the 250ml conical flask containing solution from procedure I. Label this as solution D. Empty the burette and fill it with solution C. Pipette 25cm3 of solution D and place it into an empty 250ml conical flask. Add 2 – 3 drops of phenolphthalein indicator and titrate solution C against D. Record results in table 2. Repeat the titration of solution C against solution D and complete the table 2.

i) Calculate the average volume of solution C used

ii) Calculate the number of moles of:

I. 0.3M Sodium hydroxide used

II. Hydrochloric acid in 25cm3 of solution D

III. Hydrochloric acid in 100cm3 of solution D.

IV. Hydrochloric acid in 50cm3 of solution B.

V. Hydrochloric acid that reacted with magnesium.

VI. Magnesium that reacted

22 marks


You are provided with solid E, F and G. Carry out the tests below and write your observations and inferences in the spaces provided. a) Place all the solid E in a boiling tube. Add 20cm3 of distilled water and shake until all the solid dissolves. Label this as solution E. i) To about 2cm3 of solution E in a test tube, add 4 drops of 2M Suphuric (VI) acid.

ii) To about 2cm3 of solution E in a test –tube, add 2M sodium hydroxide dropwise until excess.

iii) Place a half of solid F in a test –tube. Add 2cm3 of distilled water and shake well. Add 4 drops of this solution to about 2cm3 of solution E in a test tube.

iv) To about 2cm3 of solution E in a test tube add 2 drops of aqueous potassium iodide.

9 marks


i) Using a metallic spatula, ignite about one half of solid G in a Bunsen burner flame.

ii) Place the other half of solid G into a boiling tube. Add 15cm3 of distilled water and shake well. Label this solution G. Use the solution for the following tests.

I. Place 2cm3 of solution G in a test – tube and determine its PH.

II. To about 2cm3 of the solution, obtained in (ii) above, add 3 drops of acidified potassium manganate (VII).

III. To about 2cm3 of solution in (II) above, add 2 drops of bromine water.

iii) To the remaining solution G in the boiling tube, add the other half of solid F.

9 marks

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