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EHS Chemistry A Guide To Problem Solving in Chemistry

Earlston High School

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Problem Solving in Chemistry

Problem solving is an important part of chemistry courses in school. Problem solving questions often require the student to think about an unfamiliar reaction or process and figure out the answers to a number of questions about that process.

Although it sounds daunting, this can be done be applying a few key skills which should be practised throughout your time studying chemistry in order to master them.

These key skills are:

• Selecting data • Experimental design • Drawing a conclusion from some experimental data • Making a prediction • Processing information and presenting it appropriately (may

include graphs!) • Analysis of a text or procedure • Evaluating results or experimental techniques

The following questions have been selected from exam papers for you to practise each of these skills.

Questions in boxes are from National 5 exam papers, the rest are from General level Standard Grade papers.

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Chapter 1

Selecting and Presenting Information

You will commonly be asked to select information from a source (either the data booklet or in the stem of the question) and present it in an appropriate format.

These questions are often the most straightforward of the problem solving type questions.

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Chapter 2

Carrying out Experimental Procedures

These types of questions will test your ability to carry out experiments fairly and safely.

You will not always have carried out the experiment described in class, but you should be able to comment on good experimental design and practice.

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Chapter 3

Drawing Conclusions

These questions will present you with a set of experimental results and ask you to draw a valid conclusion from them.

You might also be asked to give explanations supported by evidence.

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Chapter 4

Making Predictions

In these questions you will be given a data set and asked to predict some missing data. You will be looking for trends or patterns and the answer will usually be a narrow range of values.

When you are analysing numerical data, you are expected to give a specific value rather than a range (don’t write “more than …” or “less than …”).

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Chapter 5

Processing and Presenting

In these questions you will be asked to use some information to work out an answer, perform a calculation based on a worked example or present the information given in some kind of graph or chart.

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Chapter 6

Evaluating

In an evaluating question, you will may asked to comment on advantages or disadvantages of a product, or discuss possible improvements to experimental design.

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Chapter 7

Short Passage Questions

Short passage questions are very common at National 5 level Chemistry. The answers may be selected from the text, or sometimes you will need to apply your knowledge of chemistry to answer them.

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Chapter 8

Unknown Reactions

There are so many families of organic compounds that we would never be able to study all of them. However, as their chemistry is very similar, some reactions of unknown chemicals can be described in a test paper and you should be able then to predict what the product will be in a similar reaction.

These questions are very common in National 5, Higher and Advanced Higher Chemistry.

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Chapter 9

Using Your Knowledge of Chemistry

There are always 2 of these questions in a chemistry paper from National 5 up to Advanced Higher. They are worth 3 marks and you would be expected to have some knowledge of the chemistry course you are studying before you can answer them.

THEY SHOULD RELATE DIRECTLY TO YOUR COURSEWORK in some way. The challenge is often to see how they are related to the coursework.

In the chemistry department we advide you to tackle these questions using an S.L. P.E.E. chain, which is a slightly modified version of the PEE chain you may have used in other subjects.

S = SURVEY (read the question carefully)

L = LIST (make a brief note of the areas of coursework the question relates to)

P = POINT (make one)

E = EVIDENCE (from the question)

E = EXPLAIN (the link between your point and the evidence)

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Eg. From the S3 Chemistry Course:

Loch Fleet is a small upland lake in the hills of Galloway, in southwest Scotland. The waters of the loch became more acidic in the 1970s and a brown trout fishery in the loch failed. The loch was neutralised and restocked in the 1990s and since then, the trout population has thrived. Using your knowledge of chemistry, comment on the change in atmospheric conditions which made the loch too acidic for fish in the 1970s, and why this has not been a problem since the 1990s.

SURVEY: Read the question – what are you actually being asked about?

This question is about acid rain and the pollution which causes it.

LIST: What are the parts of the coursework that you will have to be addressed in your answer?

What gases cause acid rain? How are they formed? How can they be removed from the waste products?

POINT: Burning fossil fuels produces gases which cause acid rain.

EVIDENCE: The loch became too acidic for fish.

EXPLAIN: This could have been caused by increasing use of fossil fuels in the 1970s. The burning of fossil fuels produces gases which dissolve in clouds and fall as acid rain.

These gases are:

• Sulfur dioxide formed when sulfur impurities in the fuel are burned.

• Nitrogen oxides formed by the sparking of air in the car engine to ignite the fuel/air mixture.

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REVIEW: Read over your answer and make sure that you have answered the question.

In this case we have not addressed the last part of the question: “…why this has not been a problem since the 1990s.”

So,

POINT: Since the 1990s catalytic converters have become common in cars, and sulfur is removed from petrol before sale.

EVIDENCE: The fish added to the loch have not died again since the 1990s.

EXPLAIN: Catalytic converters are used to turn harmful gases produced in car engines into less harmful ones. They use transition metal catalysts like platinum to break nitrogen oxides down to nitrogen and oxygen. This greatly reduces levels of nitrogen oxides into the atmosphere. However, they only work when hot.

Sulfur compounds are removed from petrol before it is sold by a process called desulfurisation.

Both these factors reduce the quantity of acidic fumes going into the atmosphere and so there is less acid rain.

This would be a very full answer – a definite 3/3.

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