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AS Chemistry 2015 M/J

bubbles1997

bubbles1997

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139
Reaction score
70
Points
38
Hi All! Feel free to post guesses and hints related to the upcoming chemistry practical. :)
 
Mathemagical

Mathemagical

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144
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53
Here are some tips for you:

1. For questions on titration, you should first perform a rough titration, then perform 2 accurate titrations. Record the initial burette reading and final burette reading for each titration, then calculate the titre. You should record everything in a table. All readings should be recorded to 2 decimal places. The titre for the 2 accurate titrations should not differ by more than 0.10cm3. Then, calculate the mean titre for the 2 accurate titrations. The mean should be given to 2 decimal places.

2. When plotting graph, draw both the horizontal and vertical axis on the graph paper correctly. Label both axis correctly and state the unit (if any). Use a suitable scale for both axis and do not use any odd scales such as 3:10. Both the x-axis and y-axis need not start from 0 (unless otherwise stated by the question). The scales should be chosen such that the points plotted on graph cover at least half of the graph paper. Plot all points on the graph accurately. The points should be accurate to half a small square. For all the points, their diameter should not be larger than half a small square. Then, draw the correct straight line or curve. When drawing the straight line or curve, it should pass through all points on the graph if possible. If this is not possible, the line or curve should pass through as many points on the graph as possible, all the points should be close to it and the number of points above and below the line or curve should be almost equal. When determining the gradient of a straight-line graph, choose 2 points on the line and draw a triangle. The distance between the 2 points chosen should be at least half the length of the line.

3. For questions on qualitative analysis, for each chemical test, you should use about 1cm depth or 2cm3 of each solution unless otherwise stated by the question. Try to record all observations and state if there is any colour change or if any precipitate forms. For any colour change, indicate both the initial and final colour, as well as the stage in which the change occurs if more than one reagents are added. If a precipitate forms, state the colour of precipitate and whether it is soluble in excess of the reagent added, and if it is soluble state the colour of the solution formed. If you see any bubbles formed, it means that gas is released, and you should carry out gas tests to determine what the gas is. Only gas tests in the Qualitative Analysis Notes at the last page of question paper should be carried out. The gas can be any one of the 6 gases, but based on the type of reagents added and your experience in doing Chemistry practical work, you may be able to predict the type of gas released and thus choose the appropriate gas test to be carried out (For example, if a metal is added to an unknown solution and gas is released, it is likely that the solution is an acid and thus hydrogen gas is released, so you should carry out the gas test for hydrogen). State that effervescence occurs and state the observations of the gas test which is positive and the type of gas released. When determining the type of an unknown chemical, it should be based on your observations of the chemical tests carried out and refer to the Qualitative Analysis Notes at the last page of question paper.

4. For any questions involving calculation, the number of significant figures of your answer should be equal to or one more than the number of significant figures of the raw value used in the calculation with the least number of significant figures. You should show all workings and do not skip any important steps. You must also write the correct unit for the final answer if it is not provided. For a calculation question which requires you to use your answer from the previous question, even if your answer for the previous question is wrong and you use it for this question causing your answer for this question to be wrong, usually you will still get full marks for this question as long as your calculation for this question is correct. This is known as 'error carried forward'.

5. For questions that require explanation or description, your answer must be very detailed. You are advised to answer in complete sentences so that your answer can be easily understood. The number of marks allocated for the question usually shows the number of points needed in your answer. Do not miss out any important points in your answer. You are allowed to write extra points in your answer, but you must be careful not to write any points with wrong facts. Marks will only be given for the correct points.

6. For all questions, you should use the correct experimental and Chemistry terms in your answer. Do not replace them with other terms that are inappropriate, even if their meaning are the same. You should spell all experimental and Chemistry terms correctly. If you can't do so, try to spell it in such a way where it sounds the same as the actual term when read out. Marks are usually not deducted for spelling errors in experimental and Chemistry terms as long as it still sounds the same and that it is not easily confused with other terms. If you spell other terms wrongly or if you make grammatical errors in your answer, marks will not be deducted for as long as the examiner can understand what you are writing. You are allowed to use suitable short forms in your answer, such as formula for chemical substances and symbols for units of physical quantities.

Hope you find this useful!
 
bubbles1997

bubbles1997

Messages
139
Reaction score
70
Points
38
Mathemagical said:
Here are some tips for you:

1. For questions on titration, you should first perform a rough titration, then perform 2 accurate titrations. Record the initial burette reading and final burette reading for each titration, then calculate the titre. You should record everything in a table. All readings should be recorded to 2 decimal places. The titre for the 2 accurate titrations should not differ by more than 0.10cm3. Then, calculate the mean titre for the 2 accurate titrations. The mean should be given to 2 decimal places.

2. When plotting graph, draw both the horizontal and vertical axis on the graph paper correctly. Label both axis correctly and state the unit (if any). Use a suitable scale for both axis and do not use any odd scales such as 3:10. Both the x-axis and y-axis need not start from 0 (unless otherwise stated by the question). The scales should be chosen such that the points plotted on graph cover at least half of the graph paper. Plot all points on the graph accurately. The points should be accurate to half a small square. For all the points, their diameter should not be larger than half a small square. Then, draw the correct straight line or curve. When drawing the straight line or curve, it should pass through all points on the graph if possible. If this is not possible, the line or curve should pass through as many points on the graph as possible, all the points should be close to it and the number of points above and below the line or curve should be almost equal. When determining the gradient of a straight-line graph, choose 2 points on the line and draw a triangle. The distance between the 2 points chosen should be at least half the length of the line.

3. For questions on qualitative analysis, for each chemical test, you should use about 1cm depth or 2cm3 of each solution unless otherwise stated by the question. Try to record all observations and state if there is any colour change or if any precipitate forms. For any colour change, indicate both the initial and final colour, as well as the stage in which the change occurs if more than one reagents are added. If a precipitate forms, state the colour of precipitate and whether it is soluble in excess of the reagent added, and if it is soluble state the colour of the solution formed. If you see any bubbles formed, it means that gas is released, and you should carry out gas tests to determine what the gas is. Only gas tests in the Qualitative Analysis Notes at the last page of question paper should be carried out. The gas can be any one of the 6 gases, but based on the type of reagents added and your experience in doing Chemistry practical work, you may be able to predict the type of gas released and thus choose the appropriate gas test to be carried out (For example, if a metal is added to an unknown solution and gas is released, it is likely that the solution is an acid and thus hydrogen gas is released, so you should carry out the gas test for hydrogen). State that effervescence occurs and state the observations of the gas test which is positive and the type of gas released. When determining the type of an unknown chemical, it should be based on your observations of the chemical tests carried out and refer to the Qualitative Analysis Notes at the last page of question paper.

4. For any questions involving calculation, the number of significant figures of your answer should be equal to or one more than the number of significant figures of the raw value used in the calculation with the least number of significant figures. You should show all workings and do not skip any important steps. You must also write the correct unit for the final answer if it is not provided. For a calculation question which requires you to use your answer from the previous question, even if your answer for the previous question is wrong and you use it for this question causing your answer for this question to be wrong, usually you will still get full marks for this question as long as your calculation for this question is correct. This is known as 'error carried forward'.

5. For questions that require explanation or description, your answer must be very detailed. You are advised to answer in complete sentences so that your answer can be easily understood. The number of marks allocated for the question usually shows the number of points needed in your answer. Do not miss out any important points in your answer. You are allowed to write extra points in your answer, but you must be careful not to write any points with wrong facts. Marks will only be given for the correct points.

6. For all questions, you should use the correct experimental and Chemistry terms in your answer. Do not replace them with other terms that are inappropriate, even if their meaning are the same. You should spell all experimental and Chemistry terms correctly. If you can't do so, try to spell it in such a way where it sounds the same as the actual term when read out. Marks are usually not deducted for spelling errors in experimental and Chemistry terms as long as it still sounds the same and that it is not easily confused with other terms. If you spell other terms wrongly or if you make grammatical errors in your answer, marks will not be deducted for as long as the examiner can understand what you are writing. You are allowed to use suitable short forms in your answer, such as formula for chemical substances and symbols for units of physical quantities.

Hope you find this useful!
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yeah i read it, thanks! :)
 
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