AH Chemistry Project won't work! Standardising HCl

My project is determining the purity of aspirin. My first experiment is standardizing hydrochloric acid. I'm using a 50 cm3 burette filled with 1M sodium hydroxide to neutralize 0.1 M of hydrochloric acid (15cm3) . The colour change i see should be red to green but it's just not working!

Any ideas??

Reply 1

Mr Lawlor

Original post by Minion212

My project is determining the purity of aspirin. My first experiment is standardizing hydrochloric acid. I'm using a 50 cm3 burette filled with 1M sodium hydroxide to neutralize 0.1 M of hydrochloric acid (15cm3) . The colour change i see should be red to green but it's just not working!

Any ideas??

What are you seeing? Is it just staying red no matter how much sodium hydroxide you add? Are you using universal indicator?

With a bit more information I might be able to help.

All the best,

Mr Lawlor

Reply 2

Minion212

OP

Original post by Mr Lawlor

What are you seeing? Is it just staying red no matter how much sodium hydroxide you add? Are you using universal indicator?

With a bit more information I might be able to help.

All the best,

Mr Lawlor

Yeah i'm using 10 drops universal indicator and i see a colour change of red to purple then it goes colourless or blue and if i keep going i use way more than 50cm3 sodium hydroxide. I'm meant to be seeing green but that never happens?

Reply 3

Mr Lawlor

Ok, so what is happening is that you are adding too much sodium hydroxide. We know this because just enough to neutralise the acid would turn the indicator green and more than enough would make the solution alkali and turn the indicator purple and then blue.

It should only take 1.5cm3 (not exactly because you don't know the exact concentration of hydrochloric acid) of 1M sodium hydroxide to neutralise 0.1M hydrochloric acid. If you must use these concentrations try going only one drop at a time and swirl the solution between drops.

If you are able to choose a different concentration of sodium hydroxide to use in the burette I would go for 0.1M. This would mean you would need about 15cm3 of the sodium hydroxide and would be a much easier volume to deal with.

Let me know how you get on.

All the best,

Mr Lawlor

Reply 4

Minion212

OP

Original post by Mr Lawlor

Ok, so what is happening is that you are adding too much sodium hydroxide. We know this because just enough to neutralise the acid would turn the indicator green and more than enough would make the solution alkali and turn the indicator purple and then blue.

It should only take 1.5cm3 (not exactly because you don't know the exact concentration of hydrochloric acid) of 1M sodium hydroxide to neutralise 0.1M hydrochloric acid. If you must use these concentrations try going only one drop at a time and swirl the solution between drops.

If you are able to choose a different concentration of sodium hydroxide to use in the burette I would go for 0.1M. This would mean you would need about 15cm3 of the sodium hydroxide and would be a much easier volume to deal with.

Let me know how you get on.

All the best,

Mr Lawlor

Ahhhh i see! So I must be adding too much at the start, it should go green before it goes purple? I've tried about 8 times and all my teacher says is try again, try again... Thanks so much!!