You are given 21.0 mL of a 5.00% solution of NaOH. The solution has a density of 1.02 g/mL. What volume of 0.0895M H2SO4 will you need to completely and exactly react (neutralize) the NaOH?
What kind of % is that? % by mass or m/v? I'll assume percent by mass. Convert 5% solution to M.
5.00% w/w means 5 g NaOH/100 g solution.
5g NaOH = how many mols. mols = grams/molar mass = 5/40 = 0.125 mols.
What's the volume. mass = volume x density or v = m/d = 100g/1.02 = 98 mL or 0.098 L. Then M = mols/L = 0.125/0.098 = 1.275M
H2SO4 + 2NaOH ==> Na2SO4 + 2H2O
mols NaOH = M x L = 1.275 x 0.021 = approx 0.0268 but you need a more accurate number here and at all of the calculations.
Convert mols NaOH to mols H2SO4 using the coefficients in the balanced equation. That's approx 0.0268 mols NaOH x (1 mol H2SO4/2 mols NaOH) = approx 0.0268 x (1/2) = approx 0.0134 mols H2SO4.
Then M H2SO4 = mols H2SO4/L H2SO4. You know M and mols, solve for L and convert to mL.