Question

Numerical: How will you prepare a 0.75% `Na_2CO_3` solution?

Answer 1

Here's a way you could do this.

Explanation:

The first thing you need to do is pick a volume for the target solution.

To make the calculations easier, I'll show you how to prepare a 0.75% w/v solution that has a total volume of 100 mL.

A solution's mass by volume percent concentration is defined as the mass of the solute, in your case sodium carbonate, divided by the total volume of the solution, and multiplied by 100.

`"%w/v" = m_"solute"/V_"sol" * 100`

You can isolate the mass of the solute to get

`m_"solute" = ("%w/v" * V_"sol")/100`

Since you want your target solution to have a volume of 100 mL and a mass by volume percent concentration of 0.75%, the mass of solute that would be needed is

`m_(Na_2CO_3) = (0.75"g"/cancel("mL") * 100cancel("mL"))/100 = "0.75 g"`

So, if you dissolve 0.75 g of sodium carbonate in enough water to make the total volume of the solution equal to 100 mL, you'll get a 0.75% w/v solution.

You can use this approach for any volume you may need the target solution to have.