Question

You prepare a solution by dissolving 3.9280 g of solid sodium hydroxide in 300 mL of distilled water in a 500 mL volumetric flask. The flask is filled to the calibration line with distilled water, stoppered, inverted and swirled several times to thoroughly mix. The prepared solution is placed into a buret and the buret is clamped onto a ring stand. The initial volume of sodium hydroxide solution in the buret is 50 mL. Calculate the concentration of the sodium hydroxide solution as prepared. Be sure to include the appropriate unit abbreviation and leave a space between the number and the unit!

Answer 1

Answer:

0.196 M

Explanation:

First, we have to calculate the moles of sodium hydroxide.

moles = mass / molar mass

moles  = 3.9280 g / (39.997 g/mol) = 0.098207 mol

It is important to realize that even though 300 mL is the volume of water firstly added to dissolve the hydroxide, the flask is then filled to the mark, meaning that the volume of the solution is 500 mL = 0.500 L.

The molar concentration of sodium hydroxide is:

$M=\frac{n_{solute}}{V_{solution}(L)} =\frac{0.098207 mol}{0.500L} =0.196 M$

The concentration is an intensive property, that is, it does not depend on the amount of matter. As a consequence, the concentration of the 50 mL of solution in the buret is the same as the concentration in the flask.