Question

Twenty-seven milliliters of an acid with an unknown concentration are titrated with a base that has a concentration of 0.55 M. The indicator changed color when 12.5 milliliters of base were added. What is the concentration of the unknown acid? 0.25 M 1.2 M

Answer 1

Twenty-seven milliliters of an acid with an unknown concentration are titrated with a base that has a concentration of 0.55 M. The indicator changed color when 12.5 milliliters of base were added. The concentration of the unknown acid is 0.25 M.

Answer 2

It should be 0.25 M. Use the formula C1*V1=C2*V2, for those values, as it is right when it changed colour. Remember to change the if those are not the same (but in your case it is, so no need this time). 

C1*V1=C2*V2
C1*27ml=0.55M*12.5ml
C1=(0.55M*12.5ml)/27ml = 0.25M