Question

How many moles of potassium chloride, KCl are needed to make 100mL of a ${\text{2}}{\text{.0M KCl}}$ solution?

Answer 1

We are already provided with the solution and its molarity. We need to apply the basic formula of molarity. It is a part of physical chemistry.

Formula used: ${\text{molarity = }}\dfrac{{{\text{moles of solute}}}}{{{\text{litres of solution}}}}$

Complete step by step answer
We already know that:
Here sodium hydroxide is the solute in the solution.
Molarity stands for moles of solute over a litre of solution, and the question. This formula only gives us the answer.
In this case, a 2.0-M potassium chloride solution contains 2.0 moles of potassium chloride, the solute, for every 1 L of solution, which means that you can write it as
$2{\text{M}} = \dfrac{{2.0{\text{moles}}(KCl)}}{{0.5{\text{L}}}}$
Also, we know that:
$1{\text{L}} = 1000{\text{mL}}$
This means that you can rewrite the molarity of the solution as
$2.0{\text{M}} = \dfrac{{2.0{\text{moles}}(KCl)}}{{{{10}^3}{\text{mL solution}}}}$
So, you need to figure out how many moles of potassium chloride must be dissolved in water to make 100.0 mL of 2.0 M solution.
$\dfrac{{{\text{moles }}\left( {{\text{KCl}}} \right)}}{{{\text{100mL solution}}}} = \dfrac{{{\text{2}}{\text{.0 moles}}}}{{{\text{1}}{{\text{0}}^{\text{3}}}{\text{mL solution}}}}$
${\text{moles}}(KCl) = 0.20{\text{moles}}$
So, there exists $0.20$ moles of KCl in the solution.

Additional Note
We should know that in order to calculate the number of moles of any substance present in the sample, we simply divide the given weight of the substance by its molar mass. Whereas The molarity (M) of a solution is the number of moles of solute dissolved in one litre of solution. To calculate the molarity of a solution, you divide the moles of solute by the volume of the solution expressed in litres.
The substance in which a solute dissolves to produce a homogeneous mixture is solvent, whereas the substance that dissolves in a solvent to produce a homogeneous mixture.

Note
We should also know that here we are dealing with molarity.
Other terms such as molarity, molality, and normality are all units of concentration in chemistry. Molarity is defined as the number of moles of solute per litre of solution. Molality is defined as the number of moles of solute per kilogram of solvent. Normality is defined as the number of equivalents per litre of solution.