Vinegar Concentration Calculation: % HC2H3O2 in a Diluted Solution

[asadpasat]

Homework Statement

After diluting 20.00mL of vinegar sample to 500.0 mL in a volumetric flask, a student titrated a 20.00 mL aliquot of this diluted solution against a 0.1120 M NaOH solution. The acetic acid requires 27.98 mL of base. What is the % HC2H3O2 in vinegar?

Homework Equations

M1V1 = M2V2

The Attempt at a Solution

I tried to find the concentration of vinegar when it is added to base. So M1(20.00mL) = (0.1120 M NaOH)(27.98 mL). But I have no idea how I am supposed to find the mass %. Do I have to apply the formula to get to the M before its dilution and then use the density of vinegar? (Even though the density is not mentioned in the problem?).
Thanks

 

[Borek]

M1V1 = M2V2

You do know where this equation comes from (and when it will fail)?

http://www.titrations.info/titration-calculation

And yes, you should know the density of the initial solution. You may initially assume it is just that of a pure water (actually it is a bit higher, but not much).