Mole, Concentration and Volume calculations

I'm stuck on this question:

What is the volume, in cm^3, of 0.25 mol dm^–3 hydrochloric acid required to neutralise 100 cm^3 of 0.125 mol dm^–3 barium hydroxide solution, Ba(OH)2(aq)?

Here's all the given information put simply:

Ba(OH)2
Concentration = 0.125 mol dm-3
Volume = 100 cm3
Moles = ?

HCl
Concentration = 0.25 mol dm-3
Volume = ?
Moles = ?

Presumably you have to use the Moles = Concentration x Volume formula.

It seems pretty simple, but I got an answer of 0.05, and the answer booklet says it's 100cm^3. I guess I'm going wrong either working out the ratio or converting units. Can anybody help?

(edited 13 years ago)

Reply 1

Femto

8

Original post by Student141

I'm stuck on this question:

What is the volume, in cm^3, of 0.25 mol dm^–3 hydrochloric acid required to neutralise 100 cm^3 of 0.125 mol dm^–3 barium hydroxide solution, Ba(OH)2(aq)?

Here's all the given information put simply:

Ba(OH)2
Concentration = 0.125 mol dm-3
Volume = 100 cm3
Moles = ?

HCl
Concentration = 0.25 mol dm-3
Volume = ?
Moles = ?

Presumably you have to use the Moles = Concentration x Volume formula.

It seems pretty simple, but I got an answer of 0.05, and the answer booklet says it's 100cm^3. I guess I'm going wrong either working out the ratio or converting units. Can anybody help?

Firstly, you need to work out the moles of Ba(OH)2 - have you done that? Quite rightly as you've mentioned

n = cv

therefore

n = (0.125 \times (100 \times 10^{-3})) = ?

Once you have this you can then use the moles with the concentration of HCl in order to find its volume; since it doesn't specify a formula for HCl, you can assume the moles are the same.

Also, I have a feeling you've forgotten to convert the volume of Barium Hydroxide into

dm^3

In this case

kcm^3 \times 10^{-3}

should do the trick.

Didn't know I was capable of providing an answer for Chemistry.

(edited 13 years ago)

Reply 2

Bubble734

4

i know you posted this 2 years ago but i'm going to answer anyway because i was stuck on it but in answering have just worked it out :smile:

1. First write out the equation: Ba(OH)2 + 2HCl --> BaCl2 + 2H2O
2. Find the moles of Ba(OH)2- 0.125 X (100/1000) (/1000 to get it to dm3 not cm3) = 0.0125
3. From the equation, one mole Ba(OH)2 reacts with 2 moles HCl, so there are twice as many moles of HCl as there are Ba(OH)2, so moles HCl=0.025
4. Volume HCl is moles/concentration so 0.025/0.25=0.1dm3
5. Convert to cm3 as that's what the question asks: 0.1 X 1000 = 100cm3 :smile:

Mole, Concentration and Volume calculations

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