How many moles of HCl are there in 50cm^3 of 0.4 mol dm^-3 solution?

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Concentration of the solution is measured as the number of moles of solvent over the volume of the solution.

Concentration = moles HCl/Volume of solution

The key in solving this problem is to make the units of the volume the same.

either you convert cm^3 to dm^3 or vice versa.

**in this case it is easier to convert cm^3 to dm^3

1cm^3 = 0.001 dm^3

50cm^3 x (0.001dm^3 /1cm^3) = 0.05 dm^3 = volume

now we go to our original formula:

Concentration = moles HCl/ volume solution

now we are looking for the moles of solute so we transform the equation to this:

moles HCl = concentraction x volume

= 0.4 moles/dm^3 x 0.05 dm^3

** = 0.02 moles HCl**

Hope this helps:)

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