Investigating acids and alkalis
In this topic you will:
- discuss questions that you can test
- plan an investigation
- think about what the results of an investigation tell you.
Key words
- remedy
- variable
Asking questions
Scientists ask questions. These are some questions about neutralisation that scientists might try to answer.
- How much lime should be added to an acid lake to neutralise it?
- Which is the best indigestion remedy (treatment for an illness or injury)?
- How much toothpaste is needed to neutralise the acid in your mouth?
Let’s look at the second question: ‘Which is the best indigestion remedy?’
It is not a very precise question. What does ‘best’ mean? Does ‘best’ mean the most pleasant tasting, the cheapest, the most effective or the most cost-effective?
Scientists need to write their question in a way that they can test. So, instead of asking: ‘Which is the best indigestion remedy?’, a scientist might ask:
‘Which indigestion powder neutralises the acid, using the least amount of powder?’
Important Concept
A good scientific question must be clear, specific, and testable. Instead of asking subjective questions like “Which is best?”, scientists reframe them into measurable and investigable forms.
Think Like a Scientist
You will develop your own scientific questions about acids and alkalis that could be investigated through experiments or research. Follow the steps below:
Step 1: Think of four different questions about acids and alkalis that you could investigate.
Step 2: Write down each question clearly in your notebook.
Step 3: Review each question and ask yourself: can this question be answered by an experiment or data collection?
Step 4: Select one question you find most interesting and prepare to share it with your teacher or class.
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A good scientific question can be tested by an experiment, leads to measurable results, and is specific and clear.
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It ensures that your question can be answered using scientific methods, which helps plan a practical and meaningful investigation.
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Example: Does the concentration of an acid affect how quickly it reacts with a metal?
Planning an investigation
When you plan to do an investigation, you have to design an experiment. If you are investigating the effect of indigestion powders on stomach acid, you cannot use your own stomach acid. You have to use a model instead, such as a beaker of acid.
There is a lot to think about.
Quick Fact
Scientists often use models in investigations when real-life materials are unsafe or impractical. A beaker of acid can simulate stomach acid safely for classroom experiments.
The things that change are called variables.
- How will you know when the powder has neutralised the acid?
- What will you see happen?
- How will you carry out the investigation?
- How will you record the results?
Important Concept
In an investigation, variables are the things you change, measure, or keep the same. Identifying and controlling them is essential for a fair test.
Think Like a Scientist
You will plan a scientific investigation based on one of the questions you created earlier. Follow these steps to develop a complete investigation plan:
Step 1: Choose one question about acids and alkalis to investigate.
Step 2: Outline how you would carry out the investigation. Think about what you would need and what you would measure.
Step 3: Create the following sections: ‘equipment list’, ‘method’, ‘safety’, and ‘results table’.
Step 4: Write up your investigation clearly on a large piece of paper or in your science notebook.
Step 5: Check that your plan is safe and practical. Make improvements if needed.
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Including safety steps helps prevent accidents and ensures that the investigation can be carried out without harm.
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A method gives step-by-step instructions so the investigation can be repeated accurately and fairly.
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You should change only one variable and keep all other conditions the same to make it a fair test.
Which powder is best at neutralising acid?
Marcus and Arun put 20 cm³ of hydrochloric acid into each of three beakers. The acid has a pH of 1. This is like the strong acid in your stomach. They also put a few drops of universal indicator in each beaker.
They add the indigestion powder, spatula by spatula, until the acid is neutralised and the universal indicator is green. They do this with each of the three powders A, B and C. They record the number of spatulas they used.
Here are Marcus and Arun’s results.
| Powder | Number of spatulas used to neutralise the acid |
|---|---|
| A | 10 |
| B | 6 |
| C | 24 |
Example
Powder B is the most effective at neutralising acid because it required the fewest spatulas (6) to reach a neutral pH, indicating it neutralises more acid per gram.
Questions
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They should wear safety goggles, gloves, and a lab coat, and handle the acid carefully to avoid spills or splashes.
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They are keeping the volume and concentration of acid, the type of indicator, and the method of adding powder the same.
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The type of indigestion powder (A, B, or C) is the variable being changed.
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The number of spatulas of powder needed to neutralise the acid.
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Powder B is the most effective because it required the fewest spatulas to neutralise the acid.
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Powder C is the least effective because it required the most spatulas to neutralise the acid.
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Not really—only one trial was done. Repeating the experiment would provide more reliable data.
| Powder | First try | Second try | Third try | Mean |
|---|---|---|---|---|
| A | 10 | 9 | 11 | 10 |
| B | 6 | 17 | 16 | 13 |
| C | 24 | 23 | 25 | 24 |
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Powder A is now the most effective because it has the lowest and most consistent mean value (10).
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The second try for Powder B (17) looks out of line compared to the first (6) and third (16).
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They might have added powder too slowly, missed the color change, or made a measurement mistake.
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They should have repeated the experiment or reviewed the data before calculating the mean.
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Probably not — it’s better to exclude outliers if there is good reason to believe the result is unreliable.