C4.7 Titrations
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What type of reaction is an acid + an alkali?
➢ Neutralisation reaction
What does an acid + base make?
➢ Salt + water
What does titration allow us to find?
➢ The amount of acid needed to react with an alkali to neutralise one another
What is the endpoint in a titration practical?
➢Where the acid and alkali have reacted completely
How do you use a pipette?
➢Fill the pipette until the bottom of the meniscus ( curved surface of the solution) lines up with the mark ➢Allow liquid to run out of the pipette and touch the tip on the side of the conical flask to drain the solution
Why do you wash a pipette with distilled water?
➢ Avoid contamination issues
What are the first few steps of carrying out a titration?
➢Measure a known volume of alkali into a conical flask using a pipette ➢ Add few drops of acid/base indicator to the solution and swirl
What do you do after you add a few drops of acid/base indicator?
➢Rinse a burette then allow some of the acid to pass through the tap ➢Burettes has markings on it to enable you to measure volumes accurately
What happens after you add a few drops of acid?
➢ Record the reading on the burette ➢ Then release more acid into the flask ➢Swirl to make sure that the two solutions are mixed
What happens after you swirl the acid and alkali together?
➢ Keep repeating until the indicator in the flask changes colour ➢ Record the reading on the burette and work out the volume of acid that has run into the flask
What is a rough estimate?
➢ On your first go you can let a large amount of acid go through the burette ➢So you have a rough estimate of how much acid is needed
What do you discard when calculating the mean?
➢ Any anomalies
What are concordant results?
➢If readings have been taken several times and the readings are identical, or close to each other
What is the final step of the titration?
➢ Calculate the concentration of acid needed to neutralise that volume of alkali
What are some examples of indicators?
➢Methyl orange ➢Phenolphthalein
What colours do Methyl orange make in acidic, neutral and alkaline solutions?
➢Red for acidic ➢Yellow for neutral ➢ Alkaline - yellow
What colours do Phenolphthalein make with acidic, neutral and alkaline solutions?
➢ Colourless for acidic ➢ Colourless for neutral ➢ Pink for Alkaline