Chapter 5 - Formulae, Equations & Amounts of substance

What is a mole?

A mole is the amount of substance that contains the same number of particles as there are atoms in exactly 12 g of carbon-12

What is Avogadro’s constant?

The number of particles in one mole (6.02 × 10²³)

How do you calculte the number of moles from particles?

number of moles = number of particles you have / number of particles of a moles

What is the molar mass?

Molar mass is the mass of 1 mole of a substance and is given the unit of g mol^-1. It is the same as the relative molecular mass.

How do you calculate the number of moles from mass?

Moles = Mass (g) / Molar mass (g mol^-1)

How do you work out the number of atoms in something?

By finding the moles, multiplying by the number of molecules and then multiplying by Avogadro’s constant.

What is concentration?

The number of moles dissolved per 1dm³ (1 litre). Measured in mol dm-³

OR

The number of grams dissolved per 1dm³. Measured in g dm^-3

How can concentration be calculated?

Concentration (mol dm ^-3) = moles / volume (dm³)

OR

Conc (g dm^-3)= mass (g) / volume (dm³)

What is empirical formula?

The empirical formula is the simplest whole number ratio of atoms of each element present in one molecule or formula unit of a compound

What is molecular formula?

The molecular formula is the formula that shows the actual number of each atom in a molecule

How do you calculate the empirical formula?

• Convert mass or % to moles (divide by Ar).

• Divide all mole values by the smallest.

• Write the simplest ratio.

How do you calculate the molecular formula?

• Calculate Mr of the empirical formula.

• Divide molecular Mr by empirical Mr.

• Multiply the empirical formula by this number.

How do you calculate percentage composition?

total mass of element in compound / total mass of compound. x 1000

How is an ionic equation different from a normal symbol equation?

They are used for any reaction involving ions in solution. They only show the reacting particles and they leave out the spectator ions.

In reactions of acids what is always produced?

A salt and water. Sometimes carbon dioxide is also formed (e.g. a reaction with a carbonate)

What is formed in precipitation reactions?

A solid precipitate