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Question: How many moles of \[NaCl\;\] are present in \[500{\text{ }}mL\] of a \[1.55\;M\] \[NaCl\] solution?...

How many moles of NaCl  NaCl\; are present in 500 mL500{\text{ }}mL of a 1.55  M1.55\;M NaClNaCl solution?

Explanation

Solution

The mole concept is very significant and useful in chemistry. It is actually the base of stoichiometry and it provides the best option to express the amounts of reactants as well as products that are consumed and formed during a chemical reaction.

Complete step by step answer:
To calculate the number of moles, we generally use the following formula:
Number of moles=Mass(g)Molar mass(gmol−1)Number{\text{ }}of{\text{ }}moles = \dfrac{{Mass(g)}}{{Molar{\text{ }}mass(gmo{l^{ - 1}})}}
In the given question we are not provided with the mass of NaClNaCl but its molarity is given. So, it means we cannot use the above mentioned formula to calculate the number of moles.
The information that is being provided to us in the question is stated below:
Volume=500 mL=0.5 L = 500{\text{ }}mL = 0.5{\text{ }}L(We have converted the units to liters by dividing it with 1000)
Molarity = 1.55  M1.55\;M
We know that solution's molarity tells you about the number of moles of solute that is present in 1 L of solution. You can use the following formula for molarity calculation:
Molarity(M)=moles of solute1 litre of solution Molarity(M) = \dfrac{{moles{\text{ }}of{\text{ solute}}}}{{1{\text{ }}litre{\text{ of }}solution{\text{ }}}}
Now, substituting the given values in the aforementioned formula of molarity, we can calculate the number of moles of NaCl  NaCl\; by rearranging the equation as shown below:
1.55=moles of NaCl0.5  moles of NaCl=0.775  1.55 = \dfrac{{moles{\text{ }}of{\text{ }}NaCl}}{{0.5{\text{ }}}} \\\ moles{\text{ }}of{\text{ }}NaCl = 0.775 \\\

Hence, 0.775 moles of NaCl  NaCl\; are present in 500 mL500{\text{ }}mL of a 1.55  M1.55\;M NaClNaCl solution.

Note: Don’t get confused between molarity and molality. Molarity is the number of moles of solute per volume of solution (litres) while Molality is the number of moles of solute per weight of solvent (kilogram). These two have a relationship as below:
Molality = (density of the solution − molarity) ×\times molecular weight of solute molarity