4. how many grams of kcl (mm = 74.55) are needed to prepare 250 ml of a 0.175 m solution?

Explanation:

Step1: Convert volume to liters

The volume $V = 250\ mL=250\times10^{- 3}\ L = 0.25\ L$.

Step2: Calculate moles of KCl

Use the formula $n = M\times V$, where $M = 0.175\ M$ and $V = 0.25\ L$. So $n=0.175\ mol/L\times0.25\ L = 0.04375\ mol$.

Step3: Calculate mass of KCl

Use the formula $m=n\times MM$, where $n = 0.04375\ mol$ and $MM = 74.55\ g/mol$. So $m = 0.04375\ mol\times74.55\ g/mol\approx3.27\ g$.

Answer:

$3.27\ g$