Question

Prepare a 2 liter 50mM sodium phosphate stock solution using mono sodium phosphate monohydrate (FW 137.990)

Answer 1

Find how many moles of the solute the solution contains:

$$n=VM=2\cdot0.05=0.1\text{ mol}.$$

The mass of mono sodium phosphate monohydrate with formula weight of 137.990 required to prepare this solution is

$$m=n\Mu=0.1\cdot137.99=13.799\text{ g}.$$

Thus, to prepare this solution, we need 13.799 g of mono sodium phosphate monohydrate (dry) and 2 L of water.