How do I calculate the Molarity of a Solution ?
Answer
Molarity, symbol M, is equal to moles divided by L of solution. M= [mols/L]. If grams are given, then we first convert to moles. If the volume is not in L, then we must convert to L.
Example: If 222 g of calcium chloride is dissolved in 500 mL of water, what is the Molarity? Solve by converting both amounts [to mols and to L] and then dividing as follows:
1] calcium chloride has a formula weight of 111 g/mol [from periodic table with CaCl(2)]. Thus, 222/111 = 2.00 mols of calcium chloride.
2] 500 mL = 0.500 L since 1000mL = 1 L.
3] M= mols/L = 2.00mols / 0.500 L = 4.00 mols/L = 4.00 M calcium chloride solution.