A concentrated solution of HF has a molarity of 8.25 M. You add 23.50 mL to a flask and then dilute with water. The mass of the final solution is 125.0 g. What is the mass percent of HF ?

Question

I can't figure it out. Please help, thank you

Answer 1

Mass percent essentially means g of HF/total grams of solution (x100%). So, in this problem we already know the total mass = 125.0 g. If we can find the mass of HF, we can then easily solve for mass percent. To find mass of HF, we will first find the moles of HF and then convert to grams of HF.

8.25 M = 8.25 moles/L

8.25 moles/L x 0.02350 L = 0.1939 moles HF used

Converting this to grams: 0.1939 moles HF x 20.01 g/mole = 3.879 g HF present

mass percent = mass HF/Total mass (x100%) = 3.879 g/125.0 g (x100%) = 3.10%