Question

what weight (in grams) of kcl is there in 2.50 liters of 0.500 m kcl solution?
0.0168 g
373 g
93.2 g
29.8 g
question 20
1 pts
you want to create a 0.25 m kcl solution using 5.00 grams of potassium chloride. how much water is needed?
270 ml
27.0 ml
16.8 ml
13.4 ml

Explanation:

Step1: Calculate moles of KCl in the first - part

Use the formula $n = M\times V$, where $M$ is molarity and $V$ is volume. Given $M = 0.500\ mol/L$ and $V=2.50\ L$.
$n = 0.500\ mol/L\times2.50\ L= 1.25\ mol$

Step2: Calculate mass of KCl

The molar mass of KCl is $M_{KCl}=39.1\ g/mol + 35.45\ g/mol=74.55\ g/mol$. Use the formula $m=n\times M$.
$m = 1.25\ mol\times74.55\ g/mol = 93.1875\ g\approx93.2\ g$

Step3: Calculate moles of KCl in the second - part

Given mass of KCl, $m = 5.00\ g$. Using $n=\frac{m}{M}$, with $M = 74.55\ g/mol$.
$n=\frac{5.00\ g}{74.55\ g/mol}\approx0.0671\ mol$

Step4: Calculate volume of the solution

Using the formula $V=\frac{n}{M}$, with $n = 0.0671\ mol$ and $M = 0.25\ mol/L$.
$V=\frac{0.0671\ mol}{0.25\ mol/L}=0.2684\ L = 268.4\ mL\approx270\ mL$

Answer:

For the first question: 93.2 g
For the second question: 270 mL