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

Sep 7, 2017

Absolutely not.........

#### Explanation:

$\text{Hydrogen chloride}$ is a room temperature gas. When it is dissolved in water we gets $\text{hydrochloric acid......}$

${\underbrace{H C l \left(g\right)}}_{\text{the gas" stackrel(H_2O)rarrunderbrace(HCl(aq))_"the acid}}$

The acid and the gas are different beasts. Concentrated hydrochloric acid has an approx. concentration of $10.6 \cdot m o l \cdot {L}^{-} 1$. In aqueous solution the hydrogen is conceived to be present as hydronium ion, ${H}_{3} {O}^{+}$, i.e. the acid has $\text{ionized}$ to give hydronium and chloride ions.

Your problem specifies (i), a mass of $H C l$, which we assume to be a gas. It specifies (ii), a volume of $H C l$, 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:

$H C l \left(g\right)$ is a source of hydronium ion, ${H}_{3} {O}^{+}$ in aqueous solution.........

We may take a tank of $H C l \left(g\right)$, and we can bleed it in to water to give an AQUEOUS solution that we could represent as $H C l \left(a q\right)$ OR, without loss of generality, ${H}_{3} {O}^{+}$ and Cl^−.

$H C l \left(g\right) \stackrel{{H}_{2} O}{\rightarrow} {\underbrace{{H}_{3} {O}^{+}}}_{\text{hydronium ion}} + C {l}^{-}$

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. $10.6 \cdot m o l \cdot {L}^{-} 1$ with respect to hydrochloric acid.

As far as anyone knows, the actual acidium ion in solution is
${H}_{5} {O}_{2}^{+}$ or ${H}_{7} {O}_{3}^{+}$, 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 ${H}_{3} {O}^{+}$, the $\text{hydronium ion}$, which is clearly the conjugate acid of ${H}_{2} O$. 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 $H {O}^{-}$ have substantial mobility in aqueous solution, and much greater mobility in solution than ions such as $N {a}^{+}$, 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.........