How many grams of cacl₂ should be dissolved in 500.0 ml of water to make a 0.20m solution of cacl₂?

0.2M means 0.2mol CaCl2/1L solution.

This question didn't give us a density of the solution so needs an assumption that the solution has equal volume to water.

xmol/0.5L=0.2M
x = 0.1

0.1mol of CaCl2 is needed. Ca=40g/mol, Cl=35.5g/mol.
CaCl2 0.1mol = (40+35.5*2)*0.1=11.1g

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