2) How is hydrogen formed at the cathode? Write a balanced half-equation for this reaction.

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Rudolf Cameron
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1 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 48 In the electrolysis of aqueous sodium chloride, except in the exceptional case of using a mercury cathode, hydrogen is the product at the cathode. The product at the anode is a mixture of oxygen and chlorine, the proportions of which will vary according to the conditions. In this practical you will investigate the way in which changing one variable affects the ratio of the two gases. ASSESSMENT This Investigation will be assessed for Design on your ability to formulate a research question and design a procedure to effectively investigate it. Design (D) Defining problem & selecting variables formulating the problem C P N Controlling variables designing for effective variable control C P N Method for collecting data designing for effective data collection C P N Total Your practical will also be assessed for Data Collection & Processing, on your ability to record appropriate data and then to use this to answer the research question in an appropriate manner. Data Collection Recording raw data recording data in an appropriate format C P N & Processing Processing raw data processing raw data correctly C P N (DCP) Presenting processed data presenting processed data appropriately C P N Total In addition, your practical will be assessed for Conclusion & Evaluation on the discussion of your results, the possible errors in the method used and suggestions for improvements. Conclusion Concluding stating a conclusion with justification C P N & Evaluation Evaluating procedure(s) evaluating weaknesses and limitations C P N (CE) Improving the investigation suggesting realistic improvements C P N Total DESIGN There are two stages to this. The first stage is that you will have to devise a method to assess the ratio of oxygen to chlorine in the product at the anode. In the second stage you will then have to decide what variable you are going to vary in the electrolysis and frame a suitable research question. Answering the pre-planning questions below may help, particularly with the first part. 1) Can electrical measurements be used to predict the total amounts of product expected at the cathode and anode? If so, what needs to be measured? 2) How is hydrogen formed at the cathode? Write a balanced half-equation for this reaction.

2 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 49 3) What will happen to the ph of the solution around the cathode? Explain 4) How is the oxygen formed at the anode? Write a balanced half-equation for this. From it deduce what volume of oxygen would be formed relative to the volume of hydrogen. 5) How is the chlorine formed at the anode? Write a balanced half-equation for this. From it deduce what volume of chlorine would be formed relative to the volume of hydrogen. 6) Would the chlorine produced affect the ph of the solution around the anode? Explain. 7) Could the relative volumes of gases at the anode and cathode be used to estimate the relative amounts of oxygen and chlorine? Explain. 8) Would it be possible to collect the oxygen-chlorine mixture and transfer it to another reaction vessel? Suggest a method. 9) Are there reagents that absorb the chlorine, but not the oxygen, so that the volume of pure oxygen could be measured? What substances would be suitable for this?

3 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 50 10) Are there reagents that would react with the chlorine so the amount of product (found by titration or other techniques) could be used to calculate the amount of chlorine present? What substances would be suitable for this? METHOD FOR DETERMINING THE OXYGEN:CHLORINE RATIO Outline the principle of the method you have chosen to determine the relative proportions of oxygen and chlorine in the product at the anode, giving appropriate chemical equations. RESEARCH QUESTION You will firstly need to decide on what aspect of this you will investigate and state this as a research question, identifying the precise variables involved: Independent variable... Dependent variable... You now need to consider other variables that could affect what you are investigating and how you can attempt to keep them constant, or at least monitor that they remain unchanged:

4 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 51 Describe specifically what data will you intend to collect. How will you use these data to answer the research question? METHOD Referring back to the Design section, write your own method for carrying out this practical giving precise details of apparatus to be used, quantities and concentrations of reagents etc.

5 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 52 DATA COLLECTION & PROCESSING Record your experimental data in an appropriate manner below. Now analyse the results in an appropriate manner to provide an answer to your research question.

6 Investigation 10 The Electrolysis Of Aqueous Sodium Chloride 53 CONCLUSION & EVALUATION a) Did your results provide the answer to your research question? Explain. If not, then explain why it failed. b) Were you satisfied at the results the Investigation produced? What were the major problems that you encountered? c) In what ways could your method have been changed so as to improve the Investigation?

MARIYA INTERNATIONAL SCHOOL. Work sheet I. Term I. Level 9 Chemistry [PAPER 1-MCQ] Name: ELECTRICITY AND CHEMISTRY

MARIYA INTERNATIONAL SCHOOL. Work sheet I. Term I. Level 9 Chemistry [PAPER 1-MCQ] Name: ELECTRICITY AND CHEMISTRY MARIYA INTERNATIONAL SCHOOL Work sheet I Term I Level 9 Chemistry [PAPER 1-MCQ] Name: ELECTRICITY AND CHEMISTRY 1. The diagram shows how aluminium is manufactured by electrolysis. What are the anode and