Titration question- I just need the answer, unless I got it wrong. Can anyone help please?

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My answer was 1.4M

Thank you in advance!

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Answer 1 · 2018-05-22T17:00:47

Yes, you are correct.

Start with the equation:

$sf(Ca(OH)_2+2HNO_3rarrCa(NO_3)_2+2H_2O)$

This tells us that 1 mole $sf(Ca(OH)_2-=)$ 2 moles $sf(HNO_3)$

Concentration = no. moles solute / volume of solution

Or:

$sf(c=n/v)$

$sf(n=m/M_r)$

$:.$ $sf(n_(Ca(OH)_2)=11/74.1=0.1484)$

$:.$ $sf([Ca(OH)_2]=0.1484/0.250=0.5937color(white)(x)"mol/l")$

The question is badly written here because you cannot be sure that the final volume of the $sf(Ca(OH)_2)$ solution is $sf(250color(white)(x)cm^3)$ .

If you add the solid the final volume may be more than $sf(250color(white)(x)cm^3)$ which would reduce the concentration.

It should have said that the calcium hydroxide is dissolved in a minimum amount of water and the solution made up to $sf(250color(white)(x)cm^3)$ .

I will assume no volume change on mixing.

In $sf(25color(white)(x)cm^3)$ of solution the number of moles of calcium hydroxide must be 1/10 of the original amount:

$sf(n_(Ca(OH)_2)=0.01484)$

From the equation, the no. moles of nitric acid must be twice this:

$sf(n_(HNO_3)=2xx0.01484=0.2969)$

$:.$ $sf([HNO_3]=0.02969/0.021=1.4color(white)(x)"mol/l")$