My compilation of slides about Chemical change.

1. CHEMICAL CHANGE
Reactions in aqueous solution

2. Ions in aqueous solution
■ Many reactions in industrial processes and in living systems take place in aqueous
solution.
■ Water is a very good solvent and therefore many substances can dissolve in it.
■ The microscopic structure of water makes it possible to dissolve other substances.

3. Polarity of water
■ The water molecule is polar.That is it has a slightly positive end and a slightly negative
end.
■ The atoms in a water molecule are held together strongly by covalent bonds to form
an angular molecule.
■ Oxygen attracts electrons to itself.
• It becomes slightly negatively charged.
• Hydrogen becomes slightly positively charged.

4. Polarity of water
■ The shape of the water molecule is important for its polarity.
■ Polarity is a difference in charges on molecules.
■ Water molecules are dipole ( they have two poles).
■ The negative and positive charges are equal, so they cancel each other and the overall
charge on a water molecule is zero.

5. Dissolution process
■ When ionic salts dissolve in water, their ions dissociate from each other.
■ This can be represented by ionic equation:

6. Dissolution processes
■ Acids are important group of covalent compounds that dissolve in water.
■ When acids dissolve in water, they ionise.
■ The new product form and so the process is a chemical change

7. Solubility in water
■ Ionic compounds are made of positive and negative ions that are tightly packed in a
crystal lattice.
■ Strong ionic bonds consists of electrostatic forces and hold the ions in position in the
solid phase.
■ Solubility is defined as the amount of a given substance that can be dissolved in a
certain amount of solvent.
■ Dissolving is a process of a solid ionic crystal breaking into its ions.

8. Solubility
Substances fall into three main categories of solubility
1. Generally, a substance is considered “soluble” if it dissolves into solution completely.
2. “Sparingly (or slightly) soluble” substances are partially soluble. A limited amount of
substance dissolves.
3. “Insoluble” substances do not dissolve at all (or a very tiny amount dissolves.)

9. Solubility of salts
■ Salts are ionic compounds that are made up of metals and none metals.
■ Salts can be soluble, sparingly soluble, and insoluble, depending on the identity of the
cation and anion.

10. Electrolytes
■ Liquids that can conduct an electric current are called electrolytes.

11. Precipitation reactions
Precipitation reactions happen when:
Two soluble salts are mixed
An exchange reaction occurs
And one of the salts formed is insoluble
• This insoluble substance is called a precipitate.

12. Reference
■ Itutor (2013) Solutions & solubility. Retrieved September 1, 2018, from
https://www.slideshare.net/itutor/solution-solubility
■ Janetra (2007) 9 Aqueous solutions. Retrieved 01 September 2018, from
https://www.slideshare.net/janetra/9-aqueous-solutions
■ Lauralici (2007) Solutions. Retrieved 01 September 2018, from
https://www.slideshare.net/lauralici/solutions