4. Chemical Changes (required practical 2 - carrying out a titration) Flashcards
What are the steps for the practical?
- Use a pipette to transfer 25cm3 of sodium hydroxide solution into a conical flask
- Add 5 drops of indicator such as methyl orange to the alkali in the conical flask
- Place the conical flask on a white tile, so we can see a colour change more clearly
- Fill a burette with sulfuric acid
- Add the acid to the alkali
- Once we start to see a colour change, add the acid drop by drop until the solution is neutral
- Read the volume of acid added from the burette
- repeat the titration several times, then calculate a mean final volume
What does the conical flask reduce the risk of?
splashing
Why is it very important that you allow the liquid to drain out of the pipette rather than blowing it out with a pipette filler?
blowing the liquid out will give you an incorrect volume
Why is it important to swirl this solution?
To make sure the acid and alkali mix
Why do we add the acid drop by drop after seeing a slight colour change?
so that we will be more likely to get the exact amount of acid needed to neutralise the alkali
How do read the volume of acid added from the burette correctly?
- you need to make sure your eye is level with the surface of the liquid
- read the burette from the bottom of the meniscus
What is the meniscus?
the natural curve of the surface of a liquid
What is the titre?
The volume of acid needed to exactly neutralise the acid
What can be measured by titration using a suitable indicator?
The volumes of acid and alkali solutions that react with each other
What colour does the solution turn if an acid or alkali is present in a litmus indicator?
acidic: red
alkaline: blue
What colour does the solution turn if an acid or alkali is present in a phenolphthalein indicator?
acidic: colourless
alkaline: pink
What colour does the solution turn if an acid of alkali is present in a methyl orange indicator?
acidic: red
alkaline: yellow
Why is a burette used to add the acid?
