Is 1.0 mL HCl equal to 1 g HCl? If not, what is it equal to and why?

1 Answer
Sep 7, 2017

Answer:

Absolutely not.........

Explanation:

#"Hydrogen chloride"# is a room temperature gas. When it is dissolved in water we gets #"hydrochloric acid......"#

#underbrace(HCl(g))_"the gas" stackrel(H_2O)rarrunderbrace(HCl(aq))_"the acid"#

The acid and the gas are different beasts. Concentrated hydrochloric acid has an approx. concentration of #10.6*mol*L^-1#. In aqueous solution the hydrogen is conceived to be present as hydronium ion, #H_3O^+#, i.e. the acid has #"ionized"# to give hydronium and chloride ions.

Your problem specifies (i), a mass of #HCl#, which we assume to be a gas. It specifies (ii), a volume of #HCl#, and we don't know the concentration of the solution.

The following is from a prior answer, which may or may not be relevant, depending on whether you are an undergrad or A level student:

#HCl(g)# is a source of hydronium ion, #H_3O^+# in aqueous solution.........

We may take a tank of #HCl(g)#, and we can bleed it in to water to give an AQUEOUS solution that we could represent as #HCl(aq)# OR, without loss of generality, #H_3O^+# and #Cl^−#.

#HCl(g) stackrel(H_2O)rarrunderbrace(H_3O^(+))_("hydronium ion") +Cl^-#

In each case this is a REPRESENTATION of what occurs in solution. If we bleed enuff gas in, we achieve saturation at a concentration of approx. #10.6*mol*L^-1# with respect to hydrochloric acid.

As far as anyone knows, the actual acidium ion in solution is
#H_5O_2^+# or #H_7O_3^+#, i.e. a cluster of 2 or 3 or 4 water molecules with an EXTRA #H^+# tacked on. We represent it in solution (without loss of generality) as #H_3O^+#, the #"hydronium ion"#, which is clearly the conjugate acid of #H_2O#. Representation of the acidium species as the protium ion, #H^+#, is also still very common.

Note that the #H^+# is quite mobile, and passes, tunnels if you like, the extra #H^+# from cluster to cluster. If you have ever played rugby, I have always liked to compare to this to when the forwards form a maul, and can pass the pill from hand to hand to the back of the maul while the maul is still formed. Of course, tunnelling, proton transfer, is more likely in a cluster of water molecules, so the analogy might not be particularly apt in that there is definite transfer of a ball in a maul, but a charge in a water cluster is conceivably tunnelled. The same applies to the transfer of an hydroxide ion. For this reason both #H^+# and #HO^-# have substantial mobility in aqueous solution, and much greater mobility in solution than ions such as #Na^+#, etc.

Depending at which level you are at (and I don't know!, which is part of the problem in answering questions on this site), you might not have to know the details at this level of sophistication. The level I have addressed here is probably 1st/2nd year undergrad.........