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Can someone explain to me about titrations in edexcel chemistry

Basically if someone could give me an idea about why the hell we even use titrations, the different indicators and their colours, some examples of titration experiments and if someone could tell me why chemicals such as sodium hydroxide are used and why do the colour changes occur

Thanks

Reply 1

AtomicMan

This is an awfully huge topic

What I will tell you without writing an essay:

Titrations are used when you want to find information about one thing when you know everything about another. E.g. finding concentration or percentage mass.

Indicators are themselves weak acids/bases, why they change is really A2 level stuff.

(edited 11 years ago)

Reply 2

ThrashMetal

You have 50ml of two solutions and you know that one solution is 2M concentration. A titration allows you to find out the molar concentration of that solution even if you don't know what the solution is by titrating it against the known solution.

Normally you would use a few drops of acid / base detector in with the known solution and add drops of the other solution until it changes colour.

The indicator you use will be able to tell you if something is a base or acid, not it's actual pH, so when your solution changes colour after a single drop you know you've reached the critical point,

Hope this helps.

Reply 3

battycatlady

Titrations are used to determine molar concentrations. You are titrating an unknown against a subtance of known concentration to find the amount of that substance that reacts exactly with what you are titrating it into.

The most common example is the sodium thiosulfate titration.

Indicators change colour within a certain PH range. Which one you use depends what type of titration it is. So, titrations have an equivilance point, which is when an exact amount of acid reacts with the equivilant amount of base. For strong acids/strong bases the equivilance point is 7.

The most common indicators are: methyl orange (red to yellow), Phenolphthalein (pink to colourless), universal indicator and one I can't remember the name of like bromo blue or something.

If I remember rightly indicators don't work with weak acid-weak base titrations.

You have to pick an idicator where the colour changes within a PH range as close as possible to the equivilance point.

As to why they change colour is to do with the fact that you are either adding OH- ions or you are adding H+ ions.

General indicator equation:

HI= H+ I-.

If you add OH- ions then they react with the H+ ions, so the equilibrium will shift to the right, wheras if you add H+ ions the equilibrium will shift to the left to remove the H+ ions. HI will give you one colour, while I- will give you a different colour. If I- and HI are present in equal amount you will see a mix of both colours. (which is why methyl orange is called so- it's a mix of red and yellow)

I used to find chem guide really useful for explaining titrations and indicators.

Sorry if this is wrong. My chemistry is rusty now I'm done with A-levels!

Reply 4

charco

Study Forum Helper

Original post by DrTK278

Check this out ...

titration in chemistry

Reply 5

DrTK278

Original post by ThrashMetal

Soo what does this have to do with electrical conductivity ???

Reply 6

ThrashMetal

Original post by DrTK278

Soo what does this have to do with electrical conductivity ???

When a solution is acidic it has H+ Ions in excess, when these ions are dissociated in a solution they can move freely. This means if you were to add a negative electrode to the solution they would be attracted to it, same with the OH-.