Chemical Changes & Structure: Formula & Calculations

Question 1

What is the prefix rule, and when can we use it?

Answer 1

The prefix rule tells us how many atoms there are in a compound.

The prefix rule can only be used if there is at least one prefix in the compound name.

If there is no prefix in front of an element this means there is one atom.

Question 2

What is valency, and when can we use the valency rule?

Answer 2

Valency is the combining power of elements, it tells us how many atoms an element can combine with.

We can use the valency rule whenever we want to, but it is recommended to use it only when a prefix is not provided.

Question 3

How can we determine the valency of an element?

Bonus: In cases where a group ion is present, how can we determine it’s valency?

Bonus: How can we work out the valency of transitional metals through their ‘roman numerals’?

Answer 3

We can determine the valency of an element based on which group it is in.

Bonus: When a group ion is present, we can use it’s number of charge to find the valency.

e.g. The sulfate ion (SO₄^2-) has a valency of 2.

This can also be found in the data-booklet (page 8).

We can work out the valency from the specific value of roman numeral applied to the metal, e.g. (III) would mean 3.

Question 4

What are the 5 steps of the valency rule?

Answer 4

S - Symbol: We write the symbols for the elements in the compound.

V - Valency: We write the valency of each element in the compound.

S - Swap: We swap the valencies with each other.

D - Divide: We divide the valency of each element by any common factors.

F - Formula: We write our formula.

Question 5

What is a group ion?

Answer 5

A group ion is a charged particle which consists of more than one atom.

The charge is on the whole group and not on one specific atom.

e.g. the sulfate ion: SO₄^2-

Question 6

What is the main indication of a group ion?

Bonus: What are the two exceptions to this rule?

Answer 6

Group ions are normally indicated by the ending ‘-ite’ or ‘-ate’.

Bonus: The exceptions towards this rule are hydroxide, and ammonium ions.

Question 7

What are the state symbols for a solid, liquid, gas, and solution (aqueous)?

Answer 7

Solid (s), Liquid (l), Gas (g), aqueous (aq).

Question 8

What is the Gram formula Mass (GFM)?

Answer 8

The gram formula mass is the mass of 1 mole of any substance.

Question 9

What is the formula linking moles, mass, and GFM?

Answer 9

Question 10

What is the formula linking moles, concentration, and volume of a solution?

Answer 10

Question 11

How would we construct a word or formula equation?

Answer 11

Reactants go on the left, with ‘+’ symbol between each, ‘→’ is used to indicate that you are moving to the products, which go on the right.

e.g. Hydrogen reacts with Nitrogen producing Ammonia

hydrogen + nitrogen → ammonia

H_{2 +} N₂ → NH_4⁺