Question

How many grams of KCL are needed to make $500\,ml$ of $2.45\,M\,$KCL?$?$

Answer 1

Hint: In this question, we are going to find the number of grams of KCL from moles.
First we are going to find the number of moles by using the formula.
Next we are going to convert the number of moles into grams by using the formula.
Simplifying it we get the result.
Hence we can get the required result.

Formula used:
Formula to find number of moles is given by
$n = \dfrac{m}{M}$
Where $n$ is the number of moles
$m$ is the given mass and
$M$ is the molar mass.
Formula to convert number of moles to grams is given by
${\text{moles = }}\dfrac{{{\text{grams}}}}{{{\text{molar}}\,{\text{mass}}}}$

Complete step by step answer:
In this question, we are going to find the number of grams of KCL.
First we are going to write the given terms:
$500\,ml$ of $2.45\,M\,$KCL
Now we are going to find the number of moles:
$n = \dfrac{m}{M}$
${\text{C = }}\dfrac{{{\text{mol}}}}{{{\text{volume}}}}$
${\text{2}}{\text{.45M = }}\dfrac{{{\text{mol}}}}{{{\text{0}}{\text{.5L}}}}$
$2.45M \times 0.5L = mol$
$mol = 1.225$
Now we are going to convert number of moles to grams using the atomic mass of K+CL
Atomic mass of KCL is written as $39.1 + 35.5$
${\text{moles = }}\dfrac{{{\text{grams}}}}{{{\text{molar}}\,{\text{mass}}}}$
${{moles \times }}\dfrac{{{\text{grams}}}}{{{\text{1}}\,{\text{mole}}}}{\text{ = grams}}$
$ \Rightarrow 1.225mol \times \dfrac{{(39.1 + 35.5)g}}{{mol}}$
Adding the terms we get,
$ \Rightarrow 1.225mol \times \dfrac{{74.6g}}{{mol}}$
Simplifying we get,
$ \Rightarrow 1.225 \times 74.6g$
Multiplying the above term we get,
$ \Rightarrow 91.4g$
Hence we get $91.4$ grams of KCL needed to make $500\,ml$ of $2.45\,M\,$KCL
Hence we get the required result.

Note: Steps to convert mole to grams:
First calculate how many moles are mentioned in the question
Next find the molar mass of the substance
Multiply both the values
To find the molecular weight of KCL:
Multiply the number of atoms for each chemical multiplied by the atomic mass. Add up the results from multiplying the numbers to obtain the molar mass for the compound.
One atom $ \times 39.0983$ potassium +one atom $ \times 35.453$ chlorine$ = 74.5513g/mol$
This is the molar mass for KCL