SAJC Prelim P4_Qns

1    Name: Shift: Class: Laboratory: ST ANDREW’S JUNIOR COLLEGE PRELIMINARY PRACTICAL EXAMINATION Chemistry Higher 2 29 August 2017 2 hours 30 minutes Additional Materials: Qualitative Analysis notes READ THESE INSTRUCTIONS FIRST. Write your name and class on all the work you hand in. Give details of the practical shift and laboratory in the boxes provided above. Write in dark blue or black pen. You may use a soft pencil for any diagrams or graphs. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all the questions in the spaces provided on the Question Paper. The use of an approved scientific calculator is expected, where appropriate. You may lose marks if you do not show your working or if you do not use appropriate units. At the end of the examination, fasten all your work securely together. The number of marks is given in the brackets [ ] at the end of each question or part question. Planning Practical 14 41 This paper consists of 18 printed pages including this page and quantitative analysis notes.

2      1 Determination of the Mr of a hydrated ethandioate salt Calcium ethanedioate is the major component of the most common type of human kidney stones. It is one of a series of salts formed from ethanedioic acid, H2C2O4. Another of these salts can be represented by the formula X2C2O4.H2O, where X is a Group 1 metal. Solution Q contains 64.5 g dm-3 of X2C2O4.H2O in deionised water. You are not provided with Q. FA 1 is a diluted solution of Q, in which 35.70 cm 3 of Q was made up to 250 cm 3 with deionised water in a graduated flask. FA 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4. FA 3 is 1.00 mol dm–3 sulfuric acid, H2SO4. In this question, you will perform a titration. The data from this titration will be used to determine:  the concentration of C 2O42- in Q,  the Mr of X2C2O4.H2O, and hence the identity of X. (a) Titration of FA 1 against FA 2 In this titration, FA 2 is run from the burette into the conical flask containing FA 1 and FA 3. Initially, the colour of the FA 2 will take some time to disappear. After some FA 2 has been added, sufficient Mn 2+(aq) ions will be present to allow the reaction to occur faster. The end-point is reached when a permanent pale pink colour is obtained. (i) 1. Fill the burette with FA 2. 2. Using a pipette, transfer 25.0 cm3 of FA 1 into the conical flask. 3. Using an appropriate measuring cylinder, transfer 50.0 cm3 of FA 3 to the same conical flask. 4. Heat this solution to about 65 °C. 5. Run FA 2 from the burette into this flask until a permanent pale pink colour is obtained. 6. Record your titration results in the space provided on page 3. Make certain that your recorded results show the precision of your working. 7. Repeat points 1 to 6 as necessary until consistent results are obtained. 8. Turn off your Bunsen burner.

3    Results