1. Chapter 13- Water the Universal Solvent
Water as a solvent
the comparison of solution processes in water for molecular substances and ionic compounds
precipitation reactions represented by balanced full and ionic equations, including states
the importance of the solvent properties of water in selected biological, domestic or industrial contexts.

2. Boardworks KS3 Science 2008 Mixtures and Solutions
What is a solution?
A solution is a special type of mixture that is made when one substance dissolves and mixes fully with another.
For example, a cup of instant coffee is a solution.
The solid that dissolves (e.g. coffee granules) is called the solute.
The liquid that does the dissolving (e.g. hot water) is called the solvent.

3. Water as a solvent
Water is sometimes called ‘the universal solvent’ because it will dissolve so many substances – in particular, salts
Polar molecules- “Like dissolves like”
A solute will dissolve if it’s attraction to the solvent is stronger than its attraction to itself.
Known as aqueous (aq) in reactions

4. What dissolves in Water?
1. Polar covalent compounds (form Hydrogen Bonds with water)
2. Polar covalent molecular compounds (ionise)
3. Ionic Compounds (dissociate)
The more polar the covalent compound is, the more likely it is to dissolve in water
“LIKE DISSOLVES LIKE”
Polar substances dissolve in polar solvents and nonpolar substances dissolve in nonpolar solvents

5. Does everything dissolve?
Boardworks KS3 Science 2008
Mixtures and Solutions
Does everything dissolve?

6. What happens when something dissolves?
Boardworks KS3 Science 2008
Mixtures and Solutions
What happens when something dissolves?
Copper sulfate is soluble in water because the copper sulfate and water particles are able to interact and mix together.
Calcium carbonate is not soluble in water because the calcium carbonate and water particles are not able to mix.
water
water
calcium carbonate
copper sulfate

7. Boardworks KS3 Science 2008 Mixtures and Solutions
Immiscible liquids
Liquids that do not mix together are described as immiscible
Why don’t they mix together? +
oil
water

8. Boardworks KS3 Science 2008 Mixtures and Solutions
Miscible liquids
Boardworks KS3 Science 2008
Mixtures and Solutions
Liquids that do mix together are described as miscible
Why do they mix together? +

9. Polar covalent compounds that can form H-Bonds with water
the comparison of solution processes in water for molecular substances and ionic compounds
Polar covalent compounds that can form H-Bonds with water
Hydrogen bonds between water molecules are broken
Hydrogen bonds between compound are broken
Hydrogen bonds between water molecules and compound are formed

10. Polar Covalent Compounds that Ionise
the comparison of solution processes in water for molecular substances and ionic compounds
Polar Covalent Compounds that Ionise
VERY polar covalent bonds can break in water, due to electrostatic attraction between them and water molecules
Polar covalent bonds within molecules break, producing Hydrogen ions and anions
A covalent bond forms between Hydrogen ion and water molecule = H3O+
Ion- dipole attractions between all ions and water molecules are formed.
Each ion is surrounded by water molecules – hydrated

11. the comparison of solution processes in water for molecular substances and ionic compounds
Ionic solid – 3D lattice of anions and cations held in fixed positions
Slight positive end of water molecule is attracted to anion in lattice
Slight negative end of water molecule is attracted to cation in lattice

12. Boardworks KS3 Science 2008 Mixtures and Solutions
Dissolving in action?

13. Ionic Bonds within lattice break
the comparison of solution processes in water for molecular substances and ionic compounds
Ionic Bonds within lattice break
Hydrogen Bonds between water molecules break
Ion-dipole attractions between ions and polar water molecules form

14. Process called Dissociation
Ions are separated from lattice and float around individually

15. Potassium chloride dissociates in water into potassium cations and chloride anions

17. Precipitation Reactions
precipitation reactions represented by balanced full and ionic equations, including states
Precipitation Reactions
Mixing solutions may produce solid = precipitate
Can separate the solid from the liquid by filtering and washing the precipitate
Filtrate: The liquid (solution) that passes through a filter

18. What will precipitate?
To determine what the precipitate will be when two solutions are mixed, exchange the ions formed and determine if any substances formed are insoluble.
Generally:
Soluble
Sodium (Na+)
Nitrate (NO3-)
Ammonium (NH4+)
Potassium (K+)
Ethanoate (CH3COO-)
Insoluble
Sulfates
Carbonates
Phosphates
Hydroxides

19. precipitation reactions represented by balanced full and ionic equations, including states
We write balanced precipitation reactions to show ion exchange in solution
The states MUST be written to show which product is the precipitate
Equations must be balanced as per normal balancing rules

20. Silver Nitrate solution mixed with Sodium Chloride solution
AgNO3 + NaCl AgCl(s) + Na+(aq) + NO3-(aq)

21. Potassium Iodide solution & Silver Nitrate solution
KI (aq) + AgNO3 (aq)  K+ (aq) + NO3- (aq) + AgI (s)

22. Precipitation reactions
Type of double displacement reaction.
Two solutions of soluble salts are mixed, resulting in an insoluble solid (precipitate) forming.
Soluble salt A(aq) + Soluble salt B(aq)
 precipitate(S) + Soluble salt C(aq)

23. Double DISPLACEMENT reactions
Double Displacement Reactions occur when a metal replaces a metal in a compound and a non-metal replaces a non-metal in a compound
Compound + compound  compound+ compound
AB(aq) + CD(aq)  AD(s) + CB(aq)
In the reactants there are A+ and B- ions and C+ and D- ions all mixed in the solution.
The reaction leads to AD becoming an insoluble product that is held in an ionic lattice, C+ and B- ions do not change from the reactants to the products and so are called spectator ions