Chapter 7 Laboratory: Solubility and Solutions 137CUTIOA nS
Concentrated hydrochloric acid is corrosive and emits
toxic and irritating fumes. Wear splash goggles, gloves,
and protective clothing at all times, and work in a well-
ventilated area or under a fume hood.z
dISoALp S : There are no items that require disposal.dRAR .m y CHERvENAk CommENTS:
Always add acid to water. Because most concentrated
acids are denser than water, they will mix more readily
when dropped into water. Water added on top of
concentrated acid may sit on top of the acid, resulting in
an interface that can generate a lot of heat and actually
cause the water to boil.POCEDURER
Because the density and mass percentage of a solution are
related, it’s possible to determine either of them, if the value of
the other is known or can be determined. For example, the label
on the bottle of reagent-grade concentrated hydrochloric acid
may specify a fairly wide range for mass percentage (such as
36% to 38%) and density (such as 1.179 to 1.189 g/mL). To get a
better value for actual concentration, I tared a 100 mL volumetric
flask, filled it to the reference line with my concentrated
hydrochloric acid, and determined the mass of the concentrated
acid. That turned out to be 118.31 g, or 1.183 g/mL.
In this lab, we’ll make up 100 mL of 1.00 M hydrochloric acid,
using our mass percentage calculations to determine how much
concentrated acid to use. (If the values listed on your own bottle
of concentrated hydrochloric acid differ significantly from these
values, recalculate amounts based on the actual values of your
concentrated hydrochloric acid.)
- If you have not already done so, put on your splash
goggles, gloves, and protective clothing. - Place a clean, dry 10 mL graduated cylinder on the
balance and tare the balance to read 0.00 g. - Using the dropper, transfer concentrated hydrochloric
acid into the graduated cylinder until the balance reads
as closely as possible to 9.854 g, which it should when
you have transferred just over 8.3 mL of acid to the
graduated cylinder. Note the mass and volume of the
concentrated HCl as accurately as possible and record
them for future use. - Fill the 100 mL volumetric flask about two-thirds full with
distilled water. - Place the funnel in the mouth of the volumetric flask, and
carefully pour the concentrated acid into the volumetric
flask. - Use the wash bottle to rinse the inside of the graduated
cylinder with several mL of water, and add the rinse water
to the volumetric flask, rinsing the funnel as you do so.
7. Repeat the rinse with another several mL of water to
make sure that the transfer is quantitative.
8. Use the water bottle to rinse the funnel again, and bring
the solution level in the volumetric flask up to within 1
cm of the reference line.
9. Remove the funnel from the mouth of the volumetric
flask, and use the dropper to add water dropwise
until the level of solution in the flask reaches the
reference line.
10. Insert the stopper in the volumetric flask and invert the
flask several times to mix the solution thoroughly.
11. Using the funnel, transfer the solution from the
volumetric flask to the labeled storage bottle.
12. Calculate the molarity to the correct number of
significant figures and record that molarity on the label.
Also record the date on the label.
13. Rinse the beaker, funnel, and volumetric flask and
stopper with tap water and then with distilled water, and
set them aside to dry.