Question

I you add 78g KBr to a final volume of 500mL, what would the final concentration be?

Answer 1

concentration of solution is number of moles per 1 L solution.
the mass of KBr added - 78 g
molar mass of KBr - 119 g/mol 
number of moles of KBr added - 78 g / 119 g/mol = 0.655 mol 
final volume - 500 mL 
the number of moles in 500 mL - 0.655 mol
therefore in 1000 mL - 0.655 mol / 500 mL x 1000 mL/L = 1.31 mol/L
concentration of KBr is 1.31 M