Amount of Substance Part 1

What is relative atomic mass?

Weighted mean mass of an atom of an element compared to 1/12 of the mass of an atom of Carbon-12 which has a mass of 12

Why are some relative atomic masses not whole numbers?

They are an average of all of the isotopes.

What is relative formula mass?

Sum of all of the atomic masses in a molecule compared to 1/12 of the mass of Carbon-12 which has a mass of 12.

What is the molar mass of an element/compound?

Mass of 1 moles of a substance

What is a mole?

The amount of substance that contains the same number of particles as the number of carbon atoms in exactly 12g of the ¹²C isotope.

What does Avogadro’s constant represent?

The number of particles present in 1 mole of any substance.

What is Avogadro’s constant?

6.02×10²³

How do you work out the number of particles?

Number of moles x (6.02 × 10²³)

What is the unit for molar mass?

g/mol

How do you work out mass?

Moles x Mr

What is the unit for moles?

mol

What is the unit for mass?

grams (g)

How do you work out concentration?

Moles/Volume

What is the unit for concentration?

mol dm^-3

What is the unit for volume?

dm³

How do you work out moles of gas?

Volume / 24dm³(000cm³)

How do you convert from cm³ to dm³

Divide by 1000 (24000cm³ = 24dm³)

Molar volume of 24dm³ is only true for gases at what temperature and pressure?

298K and 100kPa

What is empirical formula?

Simplest whole number ratio of atoms of each element in a compound

What is molecular formula?

Actual number of atoms of each element in a single molecule of a compound

How to work out empirical formula?

1. Mass

2. Mr

3. Moles = Mass/Mr

4. Divide by smallest number of moles

5. Simplest whole number ratio

Steps for combustion analysis

1. Calculate number of moles of carbon dioxide + water produced

2. Use number of moles of carbon dioxide to work out number of moles of carbon in original compound + number of moles of water to work out number of moles of hydrogen in original compound

3. Calculate mass of carbon + hydrogen

4. Calculate empirical formula

How to work out mass of oxygen in original organic molecule that has been combusted

Mass of original molecule- Mass of (carbon+hydrogen) = mass of oxygen

What are ionic equations?

Chemical equations that show only the ions participating in a reaction.

What are spectator ions?

Ions that do not participate in the reaction

Steps to write an ionic equation

1. Write balanced symbol equations including state symbols

2. Split all of the soluble salts (aq) 

3. Remove species which appear on both sides unchanged (spectator ions)

How to work out which reactant is limiting and which is in excess

The limiting reactant is the reactant with a smaller amount of moles.

What is the ideal gas equation

pV = nRT (pressure x volume = temperature x moles x gas constant (8.31))

How to convert from kPa to Pa

x 10³

How to convert from cm³ to m³

Divide by 10⁶

How to convert from dm³ to m³

Divide by 10³

How to convert from C to K

Add 273

Units for ideal gas equation

Pa x m³ = K x mol x J K^-1mol^-1

Equation for atom economy

(molecular mass of desired product/sum of molecular masses of all reactants) ×100