How many grams of a stock solution that is 87.0 percent H2SO4 by mass would be needed to make 200 grams of a 35.5 percent by mass solution?

Percent by mass is one way of expressing concentration in terms of the mass of the solute relative to the total mass of the solution. Calculation for the amount of the stock solution needed is as follows:

C1M1 = C2M2

where C is the concentration in percent by mass and M is the mass of the solution

.87 x M1 =.355 x 200

M1 = 81.61 g of the stock solution is needed.