Question

How do I prepare a solution of sodium nitrite with a concentration of 38.5 mmol/L?

Answer 1

You dissolve 2.66 g of sodium nitrite in enough water to make 1 L of solution.

Explanation:

You must measure out 38.5 mmol of sodium nitrite.

Step 1. Calculate the molar mass of `"NaNO"_2`

`M_text(r) = "Na + N + 2O" = "(22.99 + 14.01 + 2×16.00)" = 69.00`

∴ The mass of 1 mol of `"NaNO"_2` is 69.00 g.

Step 2. Calculate the mass of 38.5 mmol of `"NaNO"_2`

`"Mass of NaNO"_2 = 38.5 × 10^"-3" color(red)(cancel(color(black)("mol NaNO"_2))) × ("69.00 g NaNO"_2)/(1 color(red)(cancel(color(black)("mol NaNO"_2)))) = "2.66 g NaNO"_2`

Step 3. Prepare the solution

Transfer the `"NaNO"_2` to a 1 L volumetric flask.

Add about 300 mL of distilled water and swirl to dissolve the sodium nitrite.

Then add water until the bottom of the meniscus is just at the mark on the volumetric flask.