Calculate the mass of NaCl in a 35-mL sample of a 1.3 M NaCl solution.
Solution: here, we are going to calculate the mass of NaCl in the sample solution.
Step1:
Molarity(M) is defined as number of moles of solute dissolved in one litre (or one cubic decimetre) of solution.
Moles of solute
Molarity = ------------------------------- ------(1)
Volume of solution in litre
Step2:
In the above problem,
Volume of the solution = 35 mL = 35 / 1000 L = 0.035 L [1000 mL = 1 L]
Molarity of the solution = 1.3 M
Substituting the values in equation (1), we get,
1.3 M = moles of NaCl / 0.035 L
Therefore, moles of NaCl = 1.3 M x 0.035 L
= 0.0455 mol
Step3:
1 mol NaCl = molar mass of NaCl
0.0455 mol NaCl = 0.0455 x molar mass of NaCl
= 0.0455 x 58.44 g/mol
= 2.659 g.
Thus, the mass of NaCl is 2.659 g.
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