Video Transcript
What ions are present in an aqueous
solution of strontium chloride?
This question asks us about the
ions that exist in an aqueous solution of the salt strontium chloride. Being able to correctly list ions
present in different solutions is an important first step to be able to go on and
predict the products of electrolysis of salt solutions.
Electrolysis is a type of process
where an electric current is passed through a liquid or a solution containing ions,
which causes the substances inside to decompose, usually into their component
elements. Salts, such as strontium chloride,
are ionic compounds. Other examples include lithium
sulfate and sodium chloride. Many ionic compounds of this type
can dissociate into their constituent ions when dissolved in water. These solutions can then be used in
electrolysis to obtain pure metals and pure nonmetals from their salts.
Strontium chloride has the chemical
formula SrCl2. When strontium chloride
dissociates, or separates, into its ions in water, strontium two plus ions and
chloride one minus ions go into solution. In other words, they dissolve. We say soluble salts dissociate
into ions. Since it is an aqueous solution,
water is the solvent. Water itself can break apart into
ions, in very small amounts, namely, hydrogen ions, H+, and hydroxide ions, OH−. This process is sometimes loosely
referred to as dissociation. But the more correct term is
“ionization.”
Dissociation is the process where
charged particles in a compound separate. But ionization is the process where
new charged particles form from a compound which did not contain these charged
particles originally. Note that in reality, hydrogen ions
don’t exist for long. They quickly react with water
molecules to form hydronium ions, H3O+. This is another example of
ionization, the formation of a new ion which didn’t exist in the previous
compounds. But we will often find hydrogen
ions, H+, referred to as one of the ions which exist in water. So, these are the ions that go into
solution, or form, when strontium chloride is the solute in aqueous medium.
Note that for every one strontium
two plus ion that dissolves, two chloride ions dissolve. And for every two hydrogen ions
that form when water ionizes, only one hydroxide ion forms. However, we were not asked about
the relative numbers of each ion, only the types of ions. So, what ions are present in an
aqueous solution of strontium chloride? The answer is Sr2+, Cl−, H+, and
OH−.
