Titration confuses me, help please!

I think you've got the general idea :smile:

basically, what you are doing is filling a burette with a solution of known concentration, and running it into a conical flask filled with another solution (of known volume) and usually some sort of indicator. You run the burette solution into the other solution until a colour change (this is called the end point). As you get nearer the end point, you need to add the solution very slowly (one drop at a time) as you don't need a lot of it for the colour change. Once the colour has changed, you record the volume mark on the burette and use this to calculate the number of moles of burette solution (n=CV). There are different ways to do it, but one way is using stoichiometry, from the balanced equation find the mole ratio of the two solutions and use this to calculate the number of moles of the unknown solution and from this its concentration. You can also use the formula C1V1=C2V2, but try and stick with whichever method you've been taught. Hope that helps :smile:

Reply 4

OP

Original post by Bath_Student

You've calculated the mol in 25cm^3, not in 250cm^3. This is important because the mass (1.96g) corresponds with 250cm^3.

What must you do now?

Then, remember to subtract the molar mass of (OH)_2.

You multiply the moles by 10 and find the mass. Answer is calcium right? (39.962)

Reply 5

Bath_Student

Original post by Questioness

You multiply the moles by 10 and find the mass. Answer is calcium right? (39.962)

All correct!

Reply 6

OP

Original post by Bath_Student

All correct!

Thanks

Reply 7

Pheonixfeather3

6

Okay, so to do a titration, you want to find out the concentration of an unknown right? This could be a base or an acid, it just depends. Anyway, let's say your unknown is a hydrochloric acid, so, to find out the concentration, you need to titrate it against a base of known concentration, lets say we use NaOH at 1 mol/l, against a known volume of hydrochloric acid, say 25ml.
You need to do the titrations at least 3 times, until you get concordant results (within 0.1ml of each other).

Next, we take the average volume of NaOH from the titrations (don't use the first titration, that's just a practice, only use the two that are concordant to get the average), lets say it's 12.15ml, we use N=CV to work out the number of moles needed to neutralise the hydrochloric acid (remeber v is in litres).
From the number of moles we get, which in this example would be:
n=1x0.01215=0.01215 moles

We use the mole ration from the balanced equation, which for this reaction 1 mole NaOH gives you 1 Mole HCl, we can work out the concentration as 0.001215 moles of NaOH will react with 0.01215 moles of HCl, so;
concentration of hydrochloric acid= n/v
=0.01215/0.025 = 0.486 mol/l

Reply 8

Bath_Student

Original post by Pheonixfeather3

Okay, so to do a titration, you want to find out the concentration of an unknown right? This could be a base or an acid, it just depends. Anyway, let's say your unknown is a hydrochloric acid, so, to find out the concentration, you need to titrate it against a base of known concentration, lets say we use NaOH at 1 mol/l, against a known volume of hydrochloric acid, say 25ml.
You need to do the titrations at least 3 times, until you get concordant results (within 0.1ml of each other).

Next, we take the average volume of NaOH from the titrations (don't use the first titration, that's just a practice, only use the two that are concordant to get the average), lets say it's 12.15ml, we use N=CV to work out the number of moles needed to neutralise the hydrochloric acid (remeber v is in litres).
From the number of moles we get, which in this example would be:
n=1x0.01215=0.01215 moles

We use the mole ration from the balanced equation, which for this reaction 1 mole NaOH gives you 1 Mole HCl, we can work out the concentration as 0.001215 moles of NaOH will react with 0.01215 moles of HCl, so;
concentration of hydrochloric acid= n/v
=0.01215/0.025 = 0.486 mol/l

Lay off the drugs :smile:

Reply 9

OP

Original post by Pheonixfeather3

Okay, so to do a titration, you want to find out the concentration of an unknown right? This could be a base or an acid, it just depends. Anyway, let's say your unknown is a hydrochloric acid, so, to find out the concentration, you need to titrate it against a base of known concentration, lets say we use NaOH at 1 mol/l, against a known volume of hydrochloric acid, say 25ml.
You need to do the titrations at least 3 times, until you get concordant results (within 0.1ml of each other).

Next, we take the average volume of NaOH from the titrations (don't use the first titration, that's just a practice, only use the two that are concordant to get the average), lets say it's 12.15ml, we use N=CV to work out the number of moles needed to neutralise the hydrochloric acid (remeber v is in litres).
From the number of moles we get, which in this example would be:
n=1x0.01215=0.01215 moles

We use the mole ration from the balanced equation, which for this reaction 1 mole NaOH gives you 1 Mole HCl, we can work out the concentration as 0.001215 moles of NaOH will react with 0.01215 moles of HCl, so;
concentration of hydrochloric acid= n/v
=0.01215/0.025 = 0.486 mol/l

Thanks, you explained it really well. I understand it a lot better now. But why is the volume in litres( shouldn't it be dm^3)?

Reply 10

Bath_Student

Original post by Questioness

Thanks, you explained it really well. I understand it a lot better now. But why is the volume in litres( shouldn't it be dm^3)?

1 L = 1dm³

Reply 11

OP