CHEMISTRY AMOUNT OF SUBSTANCE

Y1- Alevel chemistry

What is the definition of the relative formula mass?

average mass of the empirical formula of an ionic compound / 1/12th the mass of one atom of C-12.

What is the definition of relative atomic mass?

Average mass of an atom of an element/ 1/12th of the mass of a C-12 atom.

What is the definition of the relative molecular mass? (same for atomic-just switch words)

The mass of an average molecule/ 1/12th the mass of one atom of C-12

What is a mole?

1 mole is the amount of substance that contains as many particles as there are atoms in exactly 12g of Carbon-12.

How many particles does 1 mole contain?

6.022×10²³ particles (Avogadro’s constant)

What is molar mass?

The mass of one mole of a substance. Units are gmol^-1 - same as relative __ mass.

Molecular formula

The actual number of atoms of each element in a compound

Empirical formula

Simplest whole number ratio of the atoms of each element present in a compound. Given for giant structures

To find the multiplier value to scale up the empirical formula, do...

Mr of molecular formula / Mr of empirical formula

The mass of one mole of particles of a substance =

The Mr of that substance in grams

Number of particles present =

Number of moles x Avogadro's constant

N2 + 3H2 → 2NH3 means...

1 molecule of nitrogen + 3 molecules of hydrogen react to form 2 molecules of ammonia

1 mole of nitrogen + 3 moles of hydrogen react to form 2 moles of ammonia

28g of nitrogen + 6g of hydrogen react to form 34g of ammonia

Reacting masses equation

Moles = Mass (in g) / Mr

Limiting reactant

The substance which is used up in a chemical reaction and controls how much product is formed

Nitrate ion

NO₃ ^-1

Valency

The number of hydrogen atoms that can combine with an atom

Group 7 valency

1

Group 6 valency

2

Group 5 valency

3

Group 4 valency

4

Sulphate ion

SO₄ ^2-

Hydroxide ion

OH^-

Hydrogen carbonate ion

HCO₃ ^-

Carbonate ion

CO₃ ^2-

Phosphate ion

PO₄ ^3-

Ammonium ion

NH₄ ⁺

Hydride ion

H^-

substance + oxygen

oxides

metal + water

metal hydroxide + hydrogen

metal + acid

salt + hydrogen

Metal oxide + acid

salt + water

Metal hydroxide + acid

salt + water

Metal carbonate + acid

salt + water + carbon dioxide

Metal hydrogencarbonate + acid

salt + water + carbon dioxide

ammonia + acid

ammonium salt

metal carbonate (on heating)

metal oxide + carbon dioxide

acid + alkali (ionic)

H+ (aq) + OH- (aq) —> H2O (l)

acid + carbonate (ionic)

2 H+ (aq) + CO32- (aq) —> CO2 (g) + H2O (l)

acid + hydrogen carbonate (ionic)

H+ (aq) + HCO3- (aq) —> CO2 (g) + H2O (l)

acid + ammonia (ionic)

H+ (aq) + NH3 (aq) —> NH4+ (aq)

acid + metal (ionic)

2 H+ (aq) + M —> M2+ (aq) + H2 (g)

precipitation (ionic)

M+ (aq) + X- (aq) —> MX (s)

Structure for limiting reactant questions:

1. Initial moles of substance

2. Change in moles of substance

3. End moles of substanc

In a back titration calculation you...

Find the moles of the substance that reacted by doing initial moles of substance - excess moles of substance. You then use this to find the mass of the other substance

Concentration

How much solute is present in a set volume. Its unit is moldm^-3 or gdm^-3

Concentration equations

Concentration (moldm^-3) = Moles (mol) / Volume (dm^3)

Concentration (gdm^-3) = Mass (g) / Volume (dm^3)

Conversion from moldm^-3 to gdm^-3

x Mr

Conversion from gdm^-3 to moldm^-3

÷ Mr

What is the formula for % yield?

actual mass product/ theoretical mass of product x 100

What is the formula for atomic economy?

total Mr of desired product/ sum of Mr of all products x 100

It is desirable to have a high atom economy because...

There is little or no waste product, so the process is more economically viable. The reaction will also be better for the environment as it will use less natural resources and less energy

What are 4 reasons why our percentage yield/atomic economy may decrease?

• Side reactions may take place

• Reactants + products can be lost when transferred

• There could be a reversible reaction.

• Reactants may be impure.

What is Boyles Law?

𝑃∝1/𝑉

What is Charles Law?

V ∝ T at a constant pressure.

What is Avogadros Law?

V ∝ n at constant temperature and pressure

What is the ideal gas equation?

PV = nRT

Under the same temperature and pressure, any number of moles of any gas will have the same...

Volume as the same number of moles of any other gas