Question

What is the molarity of a salt solution made by dissolving $240mg$ of $NaCl$ in $4mL$ of water? Assume the final volume is the same as the volume of water?

Answer 1

Hint: We have to know that, the molarity (the molarity is represented by the symbol $M$ ) is the measure of a substance in a specific volume of arrangement. Molarity is characterized as the moles of a solute for each liter of an answer. Molarity is otherwise called the molar grouping of the solution.

Complete answer:
To discover the molarity of the arrangement, we should decide the quantity of moles of solute present in precisely, $1L = {10^3}mL$ of arrangement. Notice that you definitely know the quantity of milligrams of sodium chloride, the solute, present in $4mL$ of the arrangement, so start by ascertaining the mass of solute present in ${10^3}mL$ of arrangement.
${10^3}mL{\text{ solution}} \times \dfrac{{240mg{\text{ NaCl}}}}{{4mL{\text{ olution}}}} = 60 \times {10^3}mg$
Where,
Converting the factors gram into milligram,
$1g = {10^3}mg$
Therefore,
$60 \times {10^3}mg = 60g$
The molar mass of $NaCl = 58.44g/mol$
Now, calculate the number of moles of $NaCl$ .
$60g \times \dfrac{{1mol{\text{ NaCl}}}}{{58.44g}} = 1.027mol{\text{ NaCl}}$
Since this addresses the quantity of moles of sodium chloride present in ${10^3}mL$ of arrangement, you can say that the molarity of the arrangement is equivalent to
$Molarity = 1mol/L$
The molarity of an answer is the convergence of moles of solute per liter of arrangement, $mol/L$ . The mass of $NaCl$ should be changed over to grams and afterward moles. The volume of the arrangement should be changed over to liters.
Convert $mg$ $NaCl$ to $g$ $NaCl$.
$1g = 1000mg$
Then,
$240mg{\text{ NaCl}} \times \dfrac{{1g}}{{1000mg}} = 0.24g{\text{ NaCl}}$
Now, to calculate the number of moles of $NaCl$ ,
$0.24g{\text{ NaCl}} \times \dfrac{{1mol{\text{ NaCl}}}}{{58.44g{\text{ NaCl}}}} = 0.0041mol{\text{ NaCl}}$
Finally we have to calculate the molarity of $NaCl$ ,
Then, converting the $4mL$ to $L$ ,
$1L = 1000mL$
Hence,
$4mL \times \dfrac{{1L}}{{1000mL}} = 0.004L$
The number of moles of $NaCl$ is divided by, the volume of the solution,
$M = \dfrac{{0.0041mol{\text{ NaCl}}}}{{0.004L{\text{ solution}}}} = 1mol/L$
The above answer is rounded to one significant figure due to the $4mL$ .

Note:
We have to see the convergence of the arrangement reveals to you how much solute has been broken up in the dissolvable. For instance, in the event that you add one teaspoon to two cups of water, the focus could be accounted for as one table-spoon salt for each two cup of water.