# You have 2.5L of .14M salt solution, how many grams of salt would be needed to make this solution?

Mar 9, 2018

$\text{20. g}$

#### Explanation:

The thing to recognize here is that the molarity of the solution tells you the number of moles of solute present in exactly $\text{1 L}$ of this solution.

In your case, the solution is said to have a molarity of $\text{0.14 M}$, which implies that every $\text{1 L}$ of this solution contains $0.14$ moles of salt, the solute.

Now, in order to have $\text{2.5 L}$ of $\text{0.14 M}$ salt solution, you need the solution to contain

2.5 color(red)(cancel(color(black)("L solution"))) * "0.14 moles salt"/(1color(red)(cancel(color(black)("L solution")))) = "0.35 moles salt"

In order to find the number of grams needed to have $0.35$ moles of salt, you need to use the compound's molar mass. Assuming that the salt is table salt, or sodium chloride, $\text{NaCl}$, you will have

$0.35 \textcolor{red}{\cancel{\textcolor{b l a c k}{\text{moles NaCl"))) * "58.4 g"/(1color(red)(cancel(color(black)("mole NaCl")))) = color(darkgreen)(ul(color(black)("20. g}}}}$

The answer must be rounded to two sig figs, the number of sig figs you have for your values.