HBI6X/PM1. General Certificate of Education Advanced Level Examination June A2 Externally Marked Practical Assignment.

Transcription

1 Centre Number Surname Candidate Number For Examinerʼs Use Tota Task 1 Other Names Candidate Signature Genera Certificate of Education Advanced Leve Examination June 2012 Human Bioogy HBI6X/PM1 Unit 6X A2 Externay Marked Practica Assignment Task Sheet 1 To be competed before Task Sheet 2 For submission by 15 May 2012 For this paper you must have: a ruer with miimetre measurements a cacuator. HBI6X/PM1

2 2 Aergies and the food we eat Introduction Some doctors beieve that vitamin C (ascorbic acid) heps protect the body from aergies. Task 1 - Testing for the presence of vitamin C In Task 1, you wi carry out a test for the presence of vitamin C. This test uses iodine and starch. If iodine soution is added to a soution containing starch, a bue-back coour deveops. If iodine soution is added to a soution containing vitamin C and starch, it reacts with both starch and vitamin C. Unti the iodine has reacted with a the vitamin C in the soution, any bue-back coour change ony asts for a few seconds. A permanent bue-back coour deveops after iodine has reacted with a of the vitamin C in the soution. The voume of iodine soution added to get a permanent bue-back coour can be used to cacuate the mass of vitamin C in a soution. You wi carry out two trias to hep you identify when the reaction is compete. Materias You are provided with vitamin C soution starch soution iodine soution 10 cm 3 syringe two conica fasks dropping pipette (for use with starch soution) graduated pipette or syringe pipette fier (if pipette used) timer marker pen You may ask your teacher for any other apparatus you require.

3 3 Outine method Read these instructions carefuy before you start your investigation. 1. Labe two conica fasks A and B. 2. Put 10 cm 3 of vitamin C soution and 5 drops of starch soution into fask A. 3. Fi a syringe with about 10 cm 3 of iodine soution. Record the starting voume in the syringe. 4. Add a sma voume of the iodine soution to the mixture in fask A and swir the contents of the fask aowing them to mix. 5. Repeat step 4 unti the reaction is compete. The reaction is compete when the mixture changes coour and remains cooured for onger than 20 seconds. 6. Record the fina voume of the iodine soution in the syringe. 7. Repeat steps 2 to 6 with fask B. You wi need to decide for yoursef what voume of iodine soution you shoud add each time when the reaction is compete Recording your resuts Record your resuts in the tabe. Iodine soution Fask Starting voume / cm 3 Fina voume / cm 3 Voume required to compete the reaction / cm 3 A (tria 1) B (tria 2) Turn over for Question 1 Turn over

4 4 Questions on Task 1 Answer a questions in the spaces provided. 1 You used a dropping pipette to pace 5 drops of starch soution into fask A (step 2). Did the use of a dropping pipette affect the accuracy with which you were abe to find when the reaction was compete? Expain your answer. (1 mark) 2 When you first added iodine soution to the vitamin C and starch mixture in fask A (step 4), a bue-back coour appeared but this soon disappeared. Expain why the coour disappeared. (2 marks) 3 In this investigation you did not contro temperature. Expain why this had no effect on your resut. (1 mark)

5 5 4 The 10 cm 3 of vitamin C soution in your fasks contained 10 mg vitamin C. This mass of vitamin C reacted with the voume of iodine soution that you added from the syringe. A student who carried out this investigation found that she needed 8.5 cm 3 of iodine soution to compete the reaction. Use her resut to cacuate the mass of vitamin C that reacts with 1 cm 3 of iodine soution. Show your working. 1cm 3 of iodine soution reacts with... mg vitamin C (2 marks) Turn over for the next question Turn over

6 6 5 Another student carried out a simiar investigation to you. He used DCPIP to detect vitamin C. DCPIP is a bue soution that turns coouress when it reacts with vitamin C. He used a syringe to add DCPIP to a soution containing vitamin C. 5(a) Apart from the use of DCPIP give one way in which the student s method was different from yours. (1 mark) 5(b) How woud he know when the reaction was compete? (1 mark) 5(c) What reading woud he take when the reaction was compete? Expain your answer. (2 marks) 10 END OF TASK 1

7 7 There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED

8 8 There are no questions printed on this page DO NOT WRITE ON THIS PAGE ANSWER IN THE SPACES PROVIDED Copyright 2012 AQA and its icensors. A rights reserved.