Aqueous Solution
Aqueous is a term used to define a system that involves water. The word aqueous is also applicable to describe a solution or mixture in which water is the solvent. A substance will form an aqueous solution or not, it depends on the nature of its chemical bonds.
When a substance dissolves in water, this is denoted by writing (aq) after its chemical name. Hydrophilic i.e. water-loving entities and many ionic compounds dissolve in water.
For example, table salt or sodium chloride dissolves in water and dissociates into its ions to form Na+(aq) and Cl– (aq). Hydrophobic i.e. water-fearing entities generally do not dissolve in water or form into aqueous solutions. Mixing oil and water will not result in any dissociation.
Properties of Aqueous Solution
Aqueous solutions often allow conducting electricity. Solutions that contain strong electrolytes tend to be very good electrical conductors such as seawater.
On the other hand, solutions that contain weak electrolytes tend to be poor conductors such as tap water. It is because of that strong electrolytes completely dissociate into ions in water, whereas weak electrolytes incompletely dissociate.
When chemical reactions occur between species in an aqueous solution, the reactions are usually double replacement reactions.
In such reactions, the cation from one reactant takes the place for the cation in the other reactant. Hence it is typically forming an ionic bond.
Reactions in aqueous solution may result in the products which are soluble in water or they may give a precipitate. A precipitate is a compound having low solubility and that often falls out of solution as a solid.
The terms acid, base are applicable to aqueous solutions.
Aqueous Solution Examples
A substance will form an aqueous solution or not, it depends on the nature of its chemical bonds. Some examples of aqueous solutions are cola, saltwater, rain, acid solutions, base solutions, salt solutions, etc.
Some examples of solutions that are not aqueous solutions include any liquid that does not contain water.
Vegetable oil, acetone, carbon tetrachloride, plus solutions made from these solvents are not aqueous solutions. Also if a mixture contains water but no solute dissolves in it, an aqueous solution is not formed. Like mixing sand and water will not produce an aqueous solution.
Reactions with Aqueous Solution
Many reactions in chemistry and all biological reactions take place in water. Also, we can say that these reactions take place in aqueous solution.
As we know that water has many unique properties and is available plentiful on Earth. Due to this reaction in aqueous solutions occur frequently.
Water molecules are containing two hydrogen atoms bonded to a single oxygen atom. Many substances can dissolve in water and hence give an aqueous solution.
An example of an aqueous solution is sodium chloride i.e. common salt dissolved in water. Three different types of reactions with aqueous solutions are as follows:
1. Precipitation Reactions
These reactions take place when two aqueous reactants, one solid and one liquid, react to form an insoluble product which is called a precipitate.
For example when lead nitrate mixes with potassium iodide as shown in the following chemical reaction:
Pb(NO3)2 + 2KI => PbI2 + 2KNO3
Lead iodide which produces here is not soluble product and hence is the precipitate.
2. Acid-base Reaction
As we know acid contains positive hydrogen ions. On the other hand, a base is a substance that accepts hydrogen ions and produces negative hydroxyl ions in water.
Due to acid and base reaction, a neutralization reaction occurs.
For example, a neutralization reaction occurs when HCl acid combines with NaOH to produce water and sodium chloride. The chemical equation is:
HCl + NaOH => H2O + NaCl
3. Oxidation-Reduction Reactions
Oxidation is the process in which a chemical loses electrons and hence becomes more positive. Whereas Reduction is the opposite process in which a chemical gains electrons and hence becomes more negative.
An oxidation-reduction reaction takes place between a metal and a non-metal. For example when sodium reacts with chlorine and they produce sodium chloride:
2Na + Cl2 => 2NaCl
Solved Question for You
Q: What are the following reactions examples of?
Pb2+ + 2I– → PbI2
2Ce4+ + 2I– → I2 + 2Ce3+
HOAc + NH3 → NH4+ + OAc–
- A) Acid-base reactions
- B) Precipitation, acid-base, and redox reactions, respectively
- C) Redox, acid-base, and precipitation reactions, respectively
- D) Precipitation, redox, and acid-base reactions, respectively
Ans: It is obvious that the first reaction is Precipitation forming. Second is the oxidation-reduction type. And third is the reaction of acid and base. So, option D is correct.
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