Question

How would you prepare \[100g\] of a \[10%\] \[~NaCl\] solution by mass?

Answer 1

Hint: We know that solution is made up by dissolving solute in the solvent. Here in the question the scientific terms are used to describe the amount of solute dissolve in solvent. In the question solute means $NaCl$ and the solvent is water. The molecular weight of $NaCl$is \[54.8\text{ }g/mol\] which is different from the weight we weigh in a weighing pan. The molecular weight is and the weight we weigh is $g/mol$ in grams.

Complete step-by-step answer:
Here Solution means that the amount of sodium chloride in terms of weight we have measured in the weighing pan is dissolved in water to make a solution. The dissolved in $100ml$ water to make a solution. The different ways by which the percentage of solution can be measure \[w/w,\text{ }m/m,\text{ }m/v,\text{ }w/v\] it can be read as the percentage weight of solute dissolved in weight of solvent, mass of solute in mass of solvent, mass of solute in volume of solvent, and so on. Here, in the question it is the mass of sodium chloride as solute in the given solvent.

There are different ways by which we can determine the concentration of solute in the solvent to make the solution. They are normality, molarity, molality, ppm, etc. These have different units and are used to calculate the concentration of the solution. Now, \[10%\] solution of \[~NaCl\] means \[10g\] in \[100g\] of solution;
$Percentage(mass)=\dfrac{10g\left( NaCl \right)}{100g\left( Solution \right)}\times 100$
$\Rightarrow Percentage(mass)=10$

Now that \[mass\text{ }of\text{ }water=mass\text{ }of\text{ }solution-mass\text{ }of\text{ }NaCl\]
Thus the mass of water will be $ 100g-10g=90g$
Since the density of water is \[1\text{ }g/mL,~90g\] of water will have a volume of $90mL$
To prepare a \[10%\left( weight-by-weight \right)\text{ }NaCl~\] solution, mass out \[10g\left( NaCl~ \right)\] and place it in a \[100-mL~\] volumetric flask. Add about \[80\text{ }mL~\] of water to the flask. Once the \[NaCl\] has dissolved, add more water up to the \[100-mL~\] mark. If you don't have a volumetric flask, you can use a \[100-mL~\] graduated cylinder, but it won't be as accurate.
Note: It should be noted that a lot of terms are there to represent concentration of solution but we decide on the basis of the unit or the way of representation. ppm is the most important unit used to measure concentration of the solute in parts per million levels. It is used to measure chemicals present in the water which is used for drinking purposes.