4. Reactions of Ionic Compounds

Question 1

What are the characteristics of ionic compounds?

Answer 1

• mainly have a metal and non metal
• high melting and boiling points
• solid at room temperature
• conduct electricity in liquid state (or when dissolved) but not as a solid.
• many are soluble in water (not very soluble in non polar substances)
• forms crystals that are hard and brittle

Question 2

What are the different types of bonds?

Answer 2

Metallic bonding: Positively charged metal cations arranged in a lattice with delocalised valence electrons being able to flow around them
Covalent bonding: Sharing of electrons between nuclei that bonds them together in a molecule
Ionic bonding: Bonding that forms between cations and anions.

Question 3

Ionic lattives - what are the major features of the current theory of the structure of ionic substances?

Answer 3

• IC form crystals that are composed of the 3D arrays of positive metal ions and negative non metal ions
• These arrays are called ionic network lattices and are held together by the strong electrostatic attraction - the ionic bond - between the oppositely charged ions
• the ions are arranged in a regular repeating pattern throughout the crystal. They pack together in the way that will achieve the most stable arrangement, with oppositely charged ions as close together as possible, and similarly charged ions as far apart as possible. Each cation is thus surrounded by anions and each anion by cations.
• the relative numbers of cations and anions are fixed by the requirement that the solid is neutral
• the relative sizes and numbers of the ions present determine the actual lattice structure.

Question 4

What is an empirical formula?

Answer 4

An empirical formula is a chemical formula that shows the simplest numerical ratio in which atoms are combined.

Question 5

What are the properties of ionic compounds?

Answer 5

• have a metal and non metal
• high melting and boiling points – very strong attraction between cation and anion
• solid at room temp – very strong attraction between cation and anion
• conduct electricity in liquid state (or when dissolved) – charged ions can move around
• cannot conduct electricity as a solid – attractive forces are too strong, there is no flow of charge
• Many are soluble in water – the polar molecules of water can interact with the charged particles in the ionic compound
• Form crystals that are hard and brittle

Question 6

Explain conductivity in ionic substances

Answer 6

It is not the electrons that move - only the ions are mobile in solution when molten, not the electrons.

Question 7

Tips for remembering anions

Answer 7

• anions with the -ite ending have one fewer oxygen atom than the -ate ending, but the same charge Eg nitrite, NO-2, and nitrate, NO-3
• Anions with the -ide ending mean a single atom
• adding a hydrogen decreases the negativity of the charge by one, eg. sulfate, SO2-4, and hydrogen sulfate, HSO-4

Question 8

What is a hydrate?

Answer 8

A hydrate is any compound that absorbs water in the form of H2O molecules into their chemical structure. A number of ionic compounds release water (which is part of their structure) when they decompose upon hearing. The same prefixes as organic chem is used to indicate the number of water molecules in a hydrated compound.
Written FeSO4 . 8H2O, and indicates there is 8 water molecules for each one formula of FeSO4.

Question 9

What does anhydrous mean

Answer 9

it means that a compound is not hydrated.

Question 10

What is solubility?

Answer 10

Solubility is the grams of a substance that will dissolve in an amount of a solvent at a particular temperature.

Question 11

what is an ion dipole bond?

Answer 11

an ion dipole bond is a bond between an ion and a polar molecule

Question 12

Why is water such a good solvent?

Answer 12

Because it is good at dissolving ionic compounds due to the polar nature of the bonds within water. The areas of charge form attractions with the ions in an ionic lattice and helps to pull them apart. The positive ions are attracted to the slightly negative end of the water molecules and visa versa for the opposite. These interactions are called ion dipole bonds and the separation from the lattice is called dissociation

Question 13

What is dissociation?

Answer 13

Dissociation is the process by which ions separate when an ionic substance dissolves.

Question 14

What is ionisation?

Answer 14

Ionisation is the process in which ions are formed.

Question 15

What is a precipitation reaction?

Answer 15

A precipitation reaction is where two solutions are mixed and an insoluble solid is formed.

Question 16

What are spectator ions?

Answer 16

Spectator ions are ions that are present but take no part in a reaction. They are common in a precipitation reaction and they are the ones that do not form a precipitate.

Question 17

What is a precipitate?

Answer 17

A precipitate is a solid with low solubility formed in liquid

Question 18

How to write balanced precipitation full equations.

Answer 18

1. Write out the reactants
2. write out the products (swap anions) ensuring the formulas are correct
3. Write out a skeleton equation (just reactants and products)
4. Balance the equation
5. Use the solubility table to find out if one of the products is insoluble. This is the precipitate (sometimes it may not form and on rare occasions two are formed)
6. Add states, remembering that the insoluble compound, the precipitate, must be solid.

Question 19

What is an ionic equation?

Answer 19

An ionic equation is an equation that only includes the species that have reacted, without the spectator ions