# Question #72f77

##### 1 Answer

#### Explanation:

Your starting point here is the percent concentration by mass of the target solution, which you know that must be equal to

So, what does it mean to have a *potassium chloride*,

As you know, a percent concentration by mass solution is determined by dividing the mass of the solute, which in your case is potassium chloride, by the **total mass of the solution**, and multiplying the result by

#color(blue)("%w/w" = "mass of solute"/"mass of solution" xx 100)#

Now, you know that the total mass of the solution must be

#"%w/w" = m_"KCl"/m_"solution" xx 100 implies m_"KCl" = (%"w/w" * m_"solution")/100#

Plug in your values to get

#m_"KCl" = (20.0 * "700.0 g")/100 = "140. g" -># rounded to three sig figs

So, if you need

#m_"solution" = m_"water" = m_"KCl"#

#m_"water" = "700.0 g" - "140. g" = "560. g"#

of water to make your