Question

Calculate the grams or milliliters of solute needed to prepare the following solutions.

1.)75. g of a 7.0 % (m/m) KCl solution

2.) 1250 mL of a 8.0 % (m/v) NH4Cl solution

3.) 270. mL of a 15.0 % (v/v) acetic acid solution

I really just need to know how to work the first problem then I can do the rest as long as all the rules apply

Answer 1

1.
7% m/m means 7 g solute in 100 g solution. So you want 75 g solution. How many g solute will that be. That's
7 x (75/100) = 5.25 g solute.
Place 5.25 g solute in 75-5.25 = 69.75 g H2O. I like to check these things to see that it really is 7%.
(5.25/75)*100 = 7.0% You may want to go through and adjust the significant figures. In practice you do it this way. Add 5.25 g solute to a tared beaker, add water until the balance reads 75.0 g and you have it.

Note in 2 that it is m/v so that means 8g/100 mL.
In 3 it is v/v which means mL solute/100 mL solution.