Answer
Add 15 g of sodium nitrate in less than 250 mL of water, and add more water until the solution reach this volume.
Work Step by Step
1. Find the number of moles:
$Concentration(M) = \frac{n(mol)}{V(L)}$
$0.707 = \frac{n(mol)}{0.25}$
$0.707 * 0.25 = n(mol)$
$0.177 moles = n(mol)$
2. Determine the molar mass of this compound ($NaNO_3$):
22.99* 1 + 14.01* 1 + 16* 3 = 85g/mol
3. Calculate the mass
$mm(g/mol) = \frac{mass(g)}{n(mol)}$
$mm(g/mol) * n(mol) = mass(g)$
$ 85 * 0.177 = mass(g)$
$15 = mass(g)$
So, we just need to add this mass of solid sodium nitrate in water to reach 250 mL of solution.
