[huskywolf]

Hi I have a problem here and I need some tips on how to solve it please....
Ground waters may contain hundreds of mg dm^-3CO₃^-2 ions....

I have a 0.25 L sample of hard water (ground water) ,which is titrated with 0.073 M HCl , the ground water was found to require 0.035L of HCl to adjust the pH to 5.0


I need to calculate the estimated number of moles of CO₃^-2 in the 0.25L sample of hard water?
Please...

So far I have (0.035)(0.073) = 0.0026 M  HCl is used ,I don't know what to do next?

[DrCMS]

Start with the reaction equation for the acid reacting with carbonate.

How many moles of acid react with each mole of carbonate?

How many moles of acid were used?

So how many moles of carbonate were in the sample?

[huskywolf]

Hello,
Thanks for your reply....

I'm not sure which way the equation should go?

2HCl + CO₃^2- = H₂CO₃ + Cl₂⁺² ?

For the number of moles of HCl i get seems wrong also:

n=M*v => N(HCl)=(0.0026)(0.035) =0.000091 mol?

[huskywolf]

I got 0.000182 moles of carbonate ?

It looks correct since the the ratio of moles in the equation is 2:1


Is it correct please?

[huskywolf]

Hi can someone tell me if I am correct please?

I need to be able to do this for tomorrow...
Please

[DrCMS]

So far I have (0.035)(0.073) = 0.0026 M  HCl is used ,I don't know what to do next?

Not quite you've multiplied a molarity by a volume so the answer is moles not moles per litre.

For the number of moles of HCl i get seems wrong also:

n=M*v => N(HCl)=(0.0026)(0.035) =0.000091 mol?

No you have multiplied the no. of moles of HCl calculated above by the volume used.

[Borek]

I'm not sure which way the equation should go?

2HCl + CO₃^2- = H₂CO₃ + Cl₂⁺²

What does it mean "balanced equation"?

[huskywolf]

So far I have (0.035)(0.073) = 0.0026 M  HCl is used ,I don't know what to do next?

Not quite you've multiplied a molarity by a volume so the answer is moles not moles per litre.

For the number of moles of HCl i get seems wrong also:

n=M*v => N(HCl)=(0.0026)(0.035) =0.000091 mol?

No you have multiplied the no. of moles of HCl calculated above by the volume used.

I see, thanks...

Now, I have the number of moles of HCl is 0.0026 , and the number of moles of carbonate is 0.0013 moles...
Is this correct now? Thanks

[huskywolf]

I'm not sure which way the equation should go?

2HCl + CO₃^2- = H₂CO₃ + Cl₂⁺²

What does it mean "balanced equation"?

The mass on the left must = mass on the right....

Maybe it should look like this? 2HCl + H₂CO₃=> H₂O + CO₂+ 2HCl

[huskywolf]

I'm not sure which way the equation should go?

2HCl + CO₃^2- = H₂CO₃ + Cl₂⁺²

What does it mean "balanced equation"?

The mass on the left must = mass on the right....

Maybe it should look like this? 2HCl + CO₃=> H₂O + CO₂+
 2Cl^-

Sorry ,, is the number of moles of Carbonate I calculated correct please?

[Borek]

The mass on the left must = mass on the right....

That's only part. You also need identical charge on both sides.

Maybe it should look like this? 2HCl + H₂CO₃=> H₂O + CO₂+ 2HCl

You don't start with H₂CO₃, also if you have HCl on both sides and in the same amount, you should cancel them.

1.3 mmol looks OK, but IMHO you are far from being able to solve such questions.

[huskywolf]

The mass on the left must = mass on the right....

That's only part. You also need identical charge on both sides.

Maybe it should look like this? 2HCl + H₂CO₃=> H₂O + CO₂+ 2HCl

You don't start with H₂CO₃, also if you have HCl on both sides and in the same amount, you should cancel them.

1.3 mmol looks OK, but IMHO you are far from being able to solve such questions.

Thanks for the help,

I just need plenty of practice

[DrCMS]

The balanced equation should be:

2HCl + CO₃^2-  H₂CO₃ + 2Cl^2-

also as  H₂CO₃  H₂O + CO₂


For a ground water sample it would most probably be:

2HCl + CaCO₃  CaCl₂ + H₂O + CO₂

[huskywolf]

The balanced equation should be:

2HCl + CO₃^2-  H₂CO₃ + 2Cl^2-

also as  H₂CO₃  H₂O + CO₂


For a ground water sample it would most probably be:

2HCl + CaCO₃  CaCl₂ + H₂O + CO₂

Great, Thank you very much

[Borek]

The balanced equation should be:

2HCl + CO₃^2-   H₂CO₃ + 2Cl^2-

You made the same mistake