# Help Zone

### Student Question

Hi!

I have an exercise that asks me to determine the mass of sodium hydroxide (NaOH) in a basic solution by titrating it with a 1.8 mol / L acidic solution. The titration shows a neutralization volume of 30 mL for the acid and an initial volume of 20 mL for the base. I am not sure how to find the mass.

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## Explanations (1)

• Explanation from Alloprof  Explanation from Alloprof

This Explanation was submitted by a member of the Alloprof team.

Hi!

There is a magic formula for this kind of exercise: the equivalence formula for the total neutralization of an acid or a base:

$n_{a}=n_{b}$

$C_{a}\times V_{a}=C_{b}\times V_{b}$

Here, a represents the acid and b the base. C is the concentration, V is for volume, and n is the number of moles. In this exercise, you need to find mass, so concentration is not necessary. You need to calculate the number of moles of base first while paying attention to the units:

$n_{b}=C_{a}\times V_{a}$

$n_{b}=1,8mol/L\times 0,030L=0,054mol$

With this value and the molar mass of NaOH (40.00g / mol), you can get the mass as follows:

$m=n\times M=0,054mol\times 40,00g/mol=2,16g$

I hope this answers your question. If you have other questions, don't hesitate to ask them!