Titration is a technique used to calculate the concentration of an unknown solution by using a solution with a known concentration. Put another way, it tells us the amounts of acid and alkali needed to neutralise each other. It's an important ensure that is used in the world around us, such as enabling food and pharmaceutical manufacturers to ensure their products meet quality standards.
This article will explain the titration process, including the equipment needed to calculate results. We explore the uses of this process, safety measures to follow, and common mistakes to watch out for. The type of titration focused on uses acid and alkali. This is suitable for GCSE Chemistry revision for all major exam boards, including AQA and Edexcel, as well as IGCSE students.
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Acid-alkali titration
Titration is a quantitative analysis used to determine the concentration of a solution. It's a laboratory experiment that mixes a solution of known concentration with a solution of unknown concentration. The known concentration is the titrant, while the unknown is called the analyte. The aim is to make them react.
For GCSE, the process will normally be acid-alkali titration. This is where a volume of acid and alkali is carefully mixed. The aim is to find a neutralisation point, where the acid will neutralise the alkali or vice versa. This is known as the endpoint, when the reaction is complete.
There is an indicator in the flask that will show the neutralisation point, which is normally a change in the colour of the liquid. At this point, the volume of titrant that was used is recorded and can be used in calculations.
For example, Hydrochloric acid (HCl) can be added from a burette to sodium hydroxide (NaOH) in a conical flask. When you add the acid to the alkali, you will begin to see the solution turn from pink to colourless (using phenolphthalein). This change in colour tells us the amount required to neutralise the solution.
1
What is the main purpose of a titration?
Equipment needed: Acid and alkali titration
You need the following laboratory equipment to carry out a titration. Accurate results can only be achieved using dry, clean equipment:
- Pipette - This measures a precise volume of solution, normally the alkali.
- Pipette filler - It draws liquid into the pipette safely.
- Conical flask - This flask holds the solution you are testing. The conical shape makes it easy to swirl without spillage.
- Burette - A long, graduated tube that delivers measured amounts of liquid. It normally holds the acid.
- White tile - Put this underneath the flash, so you can easily spot the colour change.
- Indicator - This is a dye that changes colour at the end-point, such as phenolphthalein or methyl orange.
- Safety goggles - To keep your eyes safe from splashes of acid or alkali.
2
Why should you place a white tile under the conical flask?
Carry out a titration practical experiment
- Measure a set volume of alkali using the pipette and pipette filter. Normally, this amount will be 25 cm3. Transfer the solution into a clean conical flask.
- Add a few drops of the indicator into the flask. Put the flask on top of a white tile.
- Fill the burette with the acid of known concentration. Ensure the acid is below eye level. Record the volume at the bottom of the meniscus (the curved surface of the liquid).
- Add the acid from the burette to the alkali gradually and slowly. Keep swirling the flask to mix the solutions.
- When the colour begins to change, add the acid a drop at a time. This will avoid overshooting and guarantee the end-point is reached.
- Record the final reading on the burette. Subtract the starting volume from the final volume to find the titre.
- Continue this process. You need at least 2 concordant results (titres within 0.10 cm³ of each other) to guarantee the accuracy of your experiment.
Record and calculate results
Use a results table when recording titration data. There should be columns for the number, starting burette reading, final reading, and the volume added (titre). The findings should match the burette scale and be recorded to two decimal places, ending in 0 or 5.
You start with a rough titre, where you estimate the endpoint. Don't include this in the calculation. Instead, only calculate the mean using concordant results (volume added/tires within 0.10 cm³ of each other).
For example:
- Run 1 - 24.60 cm³
- Run 2 - 24.70 cm³
- Mean titre = (24.60 + 24.70) / 2 = 24.65 cm³
3
Why should you only use concordant results to find the mean titre?
Common errors
Small mistakes can significantly affect the accuracy of your titration results. These are common pitfalls to watch out for:
- Parallax error - Make sure you read the burette at eye level. Don't read above or below the meniscus. This slight measurement difference can give an inaccurate volume.
- Overshoot the endpoint - It is easy to go beyond the titrant needed towards the key point of the experiment. Add a drop at a time as you approach the endpoint.
- Contaminated equipment - Make sure you thoroughly clean all equipment before use. Any residue from previous experiments can significantly alter the result. Rinse glassware with the solutions you’ll be using.
- Remove the funnel - If you forget to remove the funnel, it can cause liquid to drip into the burette. This will give a false starting reading.
- Inconsistent swirling - Keep swirling the solution evenly. Failure to be consistent can cause an uneven reaction and a delayed colour change.
4
Why should you remove the funnel from the burette?
Safety measures
Acids and alkalis can be harmful, even when using dilute solutions. Make sure to abide by the following safety rules. They will help prevent injury and ensure a safe working environment:
- Wear safety goggles - This will protect your eyes from splashing.
- Avoid skin contact - If you get acid or alkali on your body, rinse with water immediately.
- Keep glassware stable - This will prevent spills.
- Fill the burette below eye level - Looking below the burette as you fill it will reduce the risk of liquid falling towards your face.
- Handle indicators carefully - They can stain skin and clothing if improperly handled.
Real-Life applications
Titrations are used in many industries to ensure accuracy in their products. This includes the following:
- Food - This process can check acidity levels in liquids, e.g. vinegar, fruit juices, and wine.
- Medicine - Titration can measure the level of substances in blood, including glucose and drugs.
- Pharmaceuticals - It can check the exact amount of active ingredients in medicines.
- Water treatment - It can monitor and adjust the chemical levels in drinking water and swimming pools.
5
Which industry uses titrations to check acidity levels in products?
Final thoughts on Titration - GCSE Chemistry
Titration is a useful practical skill. It is an example of how precise measurement is crucial in scientific work. We have seen it is used in industries as diverse as food production, medicine, and water treatment. You can produce accurate and reliable results with this process, provided you use and correctly prepare the correct equipment, follow the method and avoid common mistakes.
For further reading, Malmesbury Education has a YouTube video of the titration method. Furthermore, StudyMind has a useful article with examples of titration calculations.
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