# Question #50bb0

##### 2 Answers

30 grams of NaOH.

#### Explanation:

Generally, the definition of % concentration for acids and bases is grams per 100 grams.

In this example, a 30% solution can be written as 30% wt./wt., which means that there are 30 g of NaOH in 100 g of final solution.

So you need to weigh out 30 g of NaOH and dissolve it in enough water to get a total mass of 100 g.

#### Explanation:

I'll assume that you mean that the desired solution is *by mass*

If the solution (which I take to be only water and aqueous sodium hydroxide) were to have a mass of

and the remaining

**Further information**:

The *solubility* of sodium hydroxide in water is seen by its solubility curve:

where the

Since there are

that dissolve, just barely above the

We can conclude that the *solubility* of sodium hydroxide in

Therefore, as long as the solution temperature is above *completely dissolve* in the water, and thus there won't be any undissolved solute left over.

However, if the solution temperature is *lower* than *will* be some undissolved