The density of a 10% solution of sulfuric acid in water is 1.0687 g/ml. What is the molarity of this solution?
The answer is 1.09 M but I do not know how to get that value.
I calculated the molar mass of H2SO4 and then I assumed that the mass was 10 grams because it is 10percent.  is this right?

Second Question:
What is the minimum pressure required for a reverse osmosis water purification system at 25°C if the local water supply contains 0.300 g of CaCO3 per liter of solution?
The answer is supposed to be  0.147 atm, but I always get 0.0734 atm which is half.
I am using the PV=nRT equation.  P = MRT, calculating Molarity by taking 0.3 divided by molar mass of CaCO3 which is 100.06 g/mol, then I get
P = (0.003)(0.8206)(298)
But it is wrong.
Is it something to do because it is osmotic pressure?

Thanks in advance!