2017 RVHS H2 Chemistry P4 Qns

River Valley High School Pg 1 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 RIVER VALLEY HIGH SCHOOL YEAR 6 PRACTICAL EXAMINATION H2 CHEMISTRY 9729 23RD AUG 2017 2 hour 30 minutes NAME CLASS 6 ( ) INDEX NO. INSTRUCTIONS TO CANDIDATES DO NOT OPEN THIS BOOKLET UNTIL YOU ARE TOLD TO DO SO. Read these notes carefully. Write your name, class and index number in the spaces at the top of this page. Give details of the practical shift and la boratory where appropriate, in the boxes provided. Write in dark blue or black pen. You may use an HB pencil for any diagrams or graph. Do not use staples, paper clips, highlighters, glue or correction fluid. Answer all 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. Qualitative Analysis Note s are printed on pages 15 and 16. _________________________________________________________________________________ Answer all the questions in the spaces provided. Shift Laboratory For Examiner’s Use 1 2 Total For Examiner’s Use 1 / 21 2 / 15 3 / 09 4 / 10 Total / 55

River Valley High School Pg 2 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 1 Determine the the percentage by mass of sodium ethanedioate in a mixture of sodium ethanedioate and ethanedioic acid. This experiment involves two steps. In step one, you will carry out a titration to find the amount of acid, H2C2O4, present in FB 3. In step two, you will carry out a second titration to find the total amount of ethanedioate ion, C 2O42-, present in FB 3. Finally, you will use the values found in the two steps to calculate the percentage by mass of sodium ethanedioate in FB 3. FB 1 is 0.100 mol dm–3 sodium hydroxide, NaOH FB 2 is 0.0200 mol dm–3 potassium manganate(VII), KMnO4 FB 3 is a mixture of aqueous sodium ethanedioate, Na2C2O4, and ethanedioic acid, H2C2O4 FB 4 is approximately 2 mol dm–3 sulfuric acid thymolphthalein indicator Read through the whole method before starting any practical work. (a) Method Step 1 1. Fill the burette labelled FB 1 with FB 1. 2. Pipette 25.0 cm 3 of FB 3 into a conical flask. 3. Add 1 dropper full of thymolphthalein. 4. Titrate FB 3 in the conical flask with FB 1 until a pale blue colour is seen. 5. Carry out as many accurate titrations as y ou think necessary to obtain consistent results. 6. Record in a suitable form below all of your burette readings and the volume of FB 1 added in each accurate titration.

River Valley High School Pg 3 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 Step 2 1. Pipette 25.0 cm 3 of FB 3 into a conical flask. 2. Using a measuring cylinder, add about 25 cm 3 of 2 mol dm –3 sulfuric acid, FB 4 , to the flask. 3. Place the conical flask on a hotplate and heat to about 65°C. 4. Fill the burette labelled FB 2 with FB 2. 5. Use an appropriate method to carefully transfer the hot conical flask onto a white tile under the burette. 6. Titrate the mixture in the conical flask with FB 2 until a permanent pale pink colour is seen. If a permanent brown colour is seen, stop the titration and begin Step 2 again. 7. Carry out as many accurate titrations as y ou think necessary to obtain consistent results. 8. Record in a suitable form below all of your burette readings and the volume of FB 2 added in each accurate titration. [3] (b) (i) From your titration results in Step 1 , obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm 3 of FB 3 required ………….. cm 3 of FB 1 [2] M4 M5 (b) (ii) Write an equation for the reaction between sodium hydroxide and ethanedioic acid to give sodium ethanedioate and water. [1] ……………………………………………………………………………………….. M6 M1 M2 M3

River Valley High School Pg 4 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 (b) (iii) Use your answer from (b)(i) to calculate the amount of sodium hydroxide, FB 1, required to react with 25.0 cm3 of FB 3 in Step 1. Amount of NaOH = ………………………. [1] M7 (b) (iv) Use your answer to (b)(iii) to determine the amount of ethanedioic acid in 25.0 cm3 of FB 3. Amount of H 2C2O4 in 25.0 cm3 of FB 3 = .............................. [1] M8 (c) (i) From your titration results in Step 2 , obtain a suitable value to be used in your calculations. Show clearly how you have obtained this value. 25.0 cm 3 of FB 3 required ………….. cm 3 of FB 2. [3] M9 M10 M11

River Valley High School Pg 5 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 (c) (ii) Use your answer from (c)(i) to calculate the amount of potassium manganate(VII), FB 2, required to react with 25.0 cm3 of FB 3 in Step 2. Amount of KMnO 4 = .............................. [1] M12 (c) (iii) The equation for the reaction between acidified manganate( VII) ions and ethanedioate ions is shown below. 2MnO4– (aq) + 5C2O42– (aq) + 16H+ (aq) ¹ 2Mn2+ (aq) + 10CO2(g) + 8H2O(l) Calculate the total amount of ethanedioate ions in 25.0 cm3 of FB 3. Total amount of C 2O42– in 25.0 cm3 of FB 3 = ……………… [1] M13 (c) (iv) Use your answers to (b)(iv) and (c)(iii) to calculate the amount of ethanedioate ions which came from the sodium ethanedioate dissolved in 25.0 cm3 of FB 3. Amount of C 2O42– from Na2C2O4 in 25.0 cm3 of FB 3 = ………………. [1] M14 (d) (i) Use your answer to (b)(iv) to calculate the mass of ethanedioic acid, H2C2O4, in 25.0 cm3 of FB 3. [Ar: H, 1.0; C, 12.0; O, 16.0] (If you were unable to answer (b)(iv), you may assume that the amount of ethanedioic acid is 6.51 × 10–4 mol.) Mass of ethanedioic acid = ........................ [1] M15

River Valley High School Pg 6 of 16 Year 6 H2 Chemistry 9729 Practical Examination 2017 (d) (ii) Use your answer to (c)(iv) to calculate the mass of sodium ethanedioate, Na2C2O4 in 25.0 cm3 of FB 3. [Ar: C, 12.0; O, 16.0; Na, 23.0] (If you were unable to answer (c)(iv), you may assume that the amount of sodium ethanedioate is 4.13 × 10–4 mol.) Mass of sodium ethanedioate = ........................ [1] M16 (d) (iii) Calculate the percentage by mass of sodium ethanedioate in FB 3. Percentage by mass of sodium ethanedioate is ...................... [1] M17 (e) (i) A student suggested that using a burette to measure the 25.0 cm 3 of acid would give a more accurate result than using a pipette. The percentage error of a 25.0 cm3 pipette is 0.24 %. Is the student correct? Explain your answer. [2] ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. ………………………………………………………………………………………. M18 M19 (e) (ii) A student decided to use a 25.0 cm 3 pipette instead of a measuring cylinder to measure the volume of FB 4 in Step 2. State and explain whether this alteration will improve the accuracy of the calculation of the percentage by mass of sodium ethanedioate in the mixture. [2] ……………………………………………………………………………………….. ……………………………………………………………………………………….. ……………………………………………………………………………………….. M20 M21 [Total: 21]