Year 11 Chemistry:~ Chapter 10 Water as a Solvent
10.4 Water as a Solvent
SOLUTES, SOLVENTS & SOLUTIONS
One of the most important properties of water is its ability to dissolve many different
substances.
Solute + Solvent  Solution
Solute: ____________________________________________________________
Solvent: ___________________________________________________________
Solution: __________________________________________________________
Give an Example:
Almost all biological processes occur in an aqueous environment. Many industrial
processes as well as most reactions carried out in the lab, occur in aqueous solutions.
When substances are dissolved in water, the particles move ________ and so
interactions between reactants are very effective.
The _________ nature of the water molecule enables water to dissolve a large number
of substances.
A solution has the following important characteristics:
 It is homogenous
 Dissolved particles are too small to see
 It is transparent to visible light (unless strongly coloured)
 The proportion of dissolved solute varies between solutions.
Homogenous: _______________________________________________________
Heterogenous: ______________________________________________________
As water is an excellent solvent, it is not found pure in nature.
Not all substances dissolve in water, oil spills at sea & most _______ have a low
solubility in water.
*Look at Table 10.4 – seawater contains at least another 40 elements. It is estimated
that the oceans of the world contain ____________ tonnes of dissolved gold.
Why do some substances dissolve?
When one substance dissolves in another:
 The particles of the __________ are ___________ from one another.
 The particles of the __________ are ___________from one another.
 The solute and the solvent particles __________ each other.
The rearrangement of particles when a solute dissolves in a solvent.
Substances that dissolve readily in water have ________or _______ covalent
bonding. They fall into three groups.
 Polar covalent molecules: Ethanol contains a polar O-H bond, so hydrogen bonding in
involved between molecules.
*Draw the structural equation for the chemical equation above.
Therefore, when ethanol dissolves in water hydrogen bonds:



The more polar the molecules of a molecular compound, the more likely it is to dissolve in
water.
Compare figures 10.18
Vitamins: B & C are soluble.
and 10.19.
Vitamins: A, D, E & K are insoluble.
In general the larger the non-polar the fraction of the molecule, the less __________
it is in water.
‘Like dissolves Like’: polar solutes will readily dissolve in
_________ solvents and non-polar solutes will readily
dissolve in __________ solvents. Eg Paints.
 Polar covalent molecular compounds that ionise
Some compounds have one or more covalent bonds that are so highly polarised that they
break when the compound is placed in water. Eg polar Hydrogen chloride bonds breaks
and the two electrons go with the Chlorine atoms and H+ forms a covalent bond with a
water molecule.
This hydrolysis process is known as ionisation. The HCl has ionised in water. The
hydronium ions and chloride ions will be surrounded by water molecules. The ions are said
to be hydrated.
Hydronium ion: ____________
When a polar covalent molecular substance ionises in water:


*Write down the chemical equation when nitric acid (HNO3) ionises in water.
 Ionic Compounds
Ionic compounds contain ____________ and ___________ ions held in a three
dimensional lattice.
*Draw figure 10.21
The ions are hydrated. The attraction between an ion and a polar molecule such as water
is described as an ion-dipole attraction. The positive and negative ions in the ionic
lattice separate from one another, this process is known as dissociation.
*Write down the chemical equation when sodium chloride dissociates in water.
*Draw structural diagrams of the above chemical equation.
*Write down the chemical equation when potassium nitrate (KNO3) dissociates in water.
When an ionic solid dissolves in water:
 Ionic bonds within the solid are ________ .
 Hydrogen bonds between water molecules are ________ .
 Ion-dipole attractions between the _____ and the polar water molecules are formed
Not all ionic compounds are water soluble, eg. Limestone.
The solubility of substances varies with temperature: most solids become _______
soluble as temperature of the solvent increases, whiles gases tend to become ______
soluble at higher temperatures.
A solubility Guide for common ionic compounds (also see pg 199)
Solubility table
Question: 24
Questions: 6, 7, 8, 9 (LHS), 10 (LHS), 11, 12 & E1abcd, E3.
Questions: 13, 14b, 17, 19, 20, 23LHS, 25ac, 28, 29, 31ace, 32, 34b & 35.
Read: The Cutting Edge (pg 203). Very interesting looks at removing oil from fur or
feathers when there are oil spills.