Question

Question #dc400

Answer 1

Dissolve 27.6 g of `"NaH"_2"PO"_4·"H"_2"O"` in enough water to make 1 L of solution.

Explanation:

Let's say you want to prepare 1 L of 0.200 mol/L `"NaH"_2"PO"_4` solution from solid `"NaH"_2"PO"_4·"H"_2"O"`.

That means you want to add 0.200 mol of the solid to enough water to make 1 L.

The molar mass of `"NaH"_2"PO"_4·"H"_2"O"` is 137.99 g/mol.

So, you would measure out

`0.200 color(red)(cancel(color(black)("mol NaH"_2"PO"_4·"H"_2"O" )))× ("137.99 g NaH"_2"PO"_4·"H"_2"O")/(1 color(red)(cancel(color(black)("mol NaH"_2"PO"_4·"H"_2"O")))) = "27.6 g NaH"_2"PO"_4·"H"_2"O"`.

You would transfer this carefully to a 1 L volumetric flask and use about 500 mL of distilled water to dissolve the solid.

Then you would add enough more distilled water to make the volume up to the 1 L mark.