Question

a chemist prepares a solution of potassium iodide (ki) by measuring out 239. g of potassium iodide into a 200. ml volumetric flask and filling the flask to the mark with water. calculate the concentration in mol/l of the chemists potassium iodide solution. be sure your answer has the correct number of significant digits.

Explanation:

Step1: Calculate moles of KI

The molar mass of KI: $K$ has a molar - mass of approximately $39.1\ g/mol$ and $I$ has a molar - mass of approximately $126.9\ g/mol$. So, the molar mass of KI, $M = 39.1+126.9=166\ g/mol$. The number of moles of KI, $n=\frac{m}{M}$, where $m = 239\ g$ and $M = 166\ g/mol$. So, $n=\frac{239\ g}{166\ g/mol}\approx1.44\ mol$.

Step2: Convert volume to liters

The volume of the solution $V = 200\ mL$. Since $1\ L=1000\ mL$, then $V = 200\ mL\times\frac{1\ L}{1000\ mL}=0.200\ L$.

Step3: Calculate the concentration

The concentration of a solution in mol/L (molarity, $M$) is given by the formula $M=\frac{n}{V}$. Substituting $n = 1.44\ mol$ and $V = 0.200\ L$ into the formula, we get $M=\frac{1.44\ mol}{0.200\ L}=7.20\ mol/L$.

Answer:

$7.20\ mol/L$