Aqueous barium chloride
“Aqueous barim chloride” is interpreted as aqueous barium chloride, meaning barium chloride dissolved in water: \(\mathrm{BaCl_2(aq)}\). The aqueous label \((aq)\) indicates that the species are hydrated and dispersed in liquid water rather than present as a solid crystal.
Dissociation and electrolyte character
Barium chloride is an ionic salt that behaves as a strong electrolyte in water. In general-chemistry treatments, strong electrolytes are represented as dissociating essentially completely into ions:
\[ \mathrm{BaCl_2(aq)\ \rightarrow\ Ba^{2+}(aq)\ +\ 2\,Cl^{-}(aq)} \]
The coefficient “2” in front of \(\mathrm{Cl^-}\) is a stoichiometric consequence of charge balance in the formula unit \(\mathrm{BaCl_2}\): one \(\mathrm{Ba^{2+}}\) pairs with two \(\mathrm{Cl^-}\) in the solid, and that same ratio carries into the ionic composition of the aqueous solution.
Ion relationships used in concentration work
When \(\mathrm{BaCl_2}\) is treated as fully dissociated, the molar concentration relationships follow directly from the dissociation stoichiometry. If the formal concentration of dissolved barium chloride is \(C\) (in \(\mathrm{mol\cdot L^{-1}}\)), then:
\[ [\mathrm{Ba^{2+}}] = C \qquad\text{and}\qquad [\mathrm{Cl^-}] = 2C \]
| Given | Resulting ion concentration | Reason |
|---|---|---|
| \(C = 0.250\ \mathrm{mol\cdot L^{-1}}\) \(\mathrm{BaCl_2(aq)}\) | \([\mathrm{Ba^{2+}}] = 0.250\ \mathrm{mol\cdot L^{-1}}\) | 1 formula unit \(\rightarrow\) 1 \(\mathrm{Ba^{2+}}\) |
| \(C = 0.250\ \mathrm{mol\cdot L^{-1}}\) \(\mathrm{BaCl_2(aq)}\) | \([\mathrm{Cl^-}] = 0.500\ \mathrm{mol\cdot L^{-1}}\) | 1 formula unit \(\rightarrow\) 2 \(\mathrm{Cl^-}\) |
Conductivity and reaction relevance in aqueous solutions
The presence of mobile \(\mathrm{Ba^{2+}}\) and \(\mathrm{Cl^-}\) ions makes aqueous barium chloride conductive. In reaction chemistry, \(\mathrm{Ba^{2+}}\) is especially important because it forms very insoluble salts with certain anions (for example, sulfate), so \(\mathrm{BaCl_2(aq)}\) is often used as a soluble source of \(\mathrm{Ba^{2+}}\) in precipitation reactions.
Common sources of error
The most frequent algebraic mistake is treating \([\mathrm{Cl^-}]\) as equal to the formal \(\mathrm{BaCl_2}\) concentration rather than \(2C\). A separate conceptual mistake is treating \(\mathrm{BaCl_2}\) as a weak electrolyte; for general-chemistry aqueous-salt problems, complete dissociation is the standard approximation.