Chemistry ATAR Year 11

Transcription

1 Chemistry ATAR Year 11 Student name: Task 11 Unit 2 Assessment type: Extended réponse Chromatography Conditions Period allowed for completion of the task: two weeks Task weighting 5% of the school mark for this unit Max Marks: /26 Semester

2 Weighting: 5%. Total marks 26. Year 11 ATAR Chemistry Term 4 Holiday Homework Due Date: The first Chemistry lesson of Term 4, at the start of the lesson. Penalty for late submission: 10 % per day or part-day. Assignments that are not type-written, not stapled, not presented as a hard copy, excessively messy or not complete may not be accepted, at your teacher s discretion. Late penalties will apply. Special Note: You will be given to take home with your assignment 1 large piece of filter paper. It is your responsibility to make sure you do this. Chromatography This term you have studied Thin Layer Chromatography (TLC), Gas Chromatography (GC) and High-Performance Liquid Chromatography / High Pressure Liquid Chromatography (HPLC). It is not practical for you to conduct these forms of chromatography at home, however a form of chromatography similar to TLC that you can conduct at home is paper chromatography. You are to conduct paper chromatography at home using thin strips of filter paper and food dye. You will submit the dried chromatograph (the filter paper with the separated colours) and you will answer questions about this method, including comparing it to other methods of chromatography. Conducting the paper chromatography An experiment similar in some ways, but not exactly the same as ours, can be seen here. Note that we are using food dyes, not ink from a marker. Materials required Food dyes 3 different colours e.g. blue, green and red. These can be obtained cheaply at the supermarket. Filter paper given to you at school. If this is not available you can use coffee filter paper, available at the supermarket. 4 clear drinking glasses. A pencil and a ruler Water Method Cut the filter paper you have been given so that you have 4 strips about 1 cm wide and about 1 cm longer than the height of your drinking glasses. Keep the rest of the filter paper as spare in case you make a mistake or want to repeat your procedure. Rule a pencil line about 1 cm above one end of the filter paper strips. Page 1

3 On to each of the first three strips of filter paper place a single small drop of one colour of food dye (e.g. red, blue or green) on the pencil line. The tip of a pencil can be used to transfer the small drop of food dye. On the fourth strip of filter paper place a single drop of a mixture of 2 or 3 different colours of food dye on the pencil line. Place water in each glass to a depth of 5 mm. Place each strip of filter paper in a separate drinking glass so that the ink spot is just above the top of the water. Leave them there until the water has moved up almost to the top of the filter paper. Take the filter paper strips out of the glass, mark with a pencil where the water has reached and then let them dry out. Analysis of Results. 1. a) Paste your chromatographs (the dried pieces of filter paper) into your assignment. [4 marks, 1 mark each] b) Determine Rf for each food dye colour. Make it clear to the examiner how you did this by labelling what you measured on your chromatographs. Also show your calculations. [4 marks, 1 mark each] c) Did chromatography reveal that any of the pure food colours (red, green or blue) were in fact mixtures? Explain your answer. [2 marks] d) Suggest at least three possible reasons why the different colours travelled at different speeds up the filter paper. [1 mark for 3 reasons] The paper chromatography you have conducted is similar in some ways to TLC. Watch this video about TLC You are to compare and contrast the paper chromatography that you conducted with the Thin Layer Chromatography that you saw conducted on the above video. You should list a total of at least 10 differences and/or similarities between the two methods. You can present this answer as a table or as a set of numbered points. You can list from 0 to 10 differences and from 0 to 10 similarities, so that the total number of differences and similarities is at least 10. See Appendix A at the back of this assignment regarding answering compare and contrast questions. Unlike in Appendix A, you should use full sentences in your answer. [10 marks; 1 mark for each similarity or difference between the methods] Page 2

4 3. To answer this final question you will need to research about Gas Chromatography and High Pressure Liquid Chromatography (also called High-Performance Liquid Chromatography). Answer the following question in the form of an extended response without exceeding 200 words. Question: Is the paper chromatography you performed more similar to gas chromatography, or more similar to high-pressure liquid chromatography? Justify your choice by referring to at least 5 aspects of the methods you discuss. [5 marks] Page 3

5 Appendix A Here is a guide to how to correctly answer compare and contrast questions. Compare means state a similarity between two things, in a single sentence beginning with the word Both. Contrast means state a difference between two things, in a single sentence containing the word whereas. Example question: Compare and contrast apples and bananas. Tick means a correctly stated compare or contrast. Cross means not correctly stated. Both apples and bananas are fruit. Apples are fruit. X Bananas are fruit. X Apples can be red or green whereas bananas are yellow. Bananas are yellow. X Bananas are yellow and apples are fruit. X Bananas are yellow whereas apples are fruit. X Page 4