(CHEM) Topic 1 - Stoichiometry

Elements

Primary constituents of matter that cannot be chemically broken down into simpler substances

Compounds

Atoms of different elements chemically bonded together in a fixed ratio

Mixtures

More than one element or compound in no fixed ratio not chemically bonded together that can be separated by physical methods

Homogenous mixture (definition + example)

All components are in the same phase (air)

Heterogenous mixture (definition + example)

Components are in different phases and there is a physical boundary between them (oil and water)

5 physical methods of separation

• Solvation

• Filtration

• Evaporation and recrystallisation

• Distillation

• Separatory funnel

• Chromatography

How to separate a mixture of one insoluable solid and one liquid

By filtration

How to separate a mixture of one soluable and one insoluble solid

By evaporation and recrystallisation

Describe distillation

Volatile solvent boils to form a gas which condenses and is collected

How to separate a mixture of two immiscible liquids

By using a separatory funnel

How does chromatography work

It separates components based on relative attractions

What is the advantaege of thin-layer chromatography

Components can be recovered pure

Retardation factor value formula

R_F = (distance moved by solute) / (distance moved by solvent)

Gas to solid

Deposition

Solid to gas

Sublimation

Gas to liquid

Condensation

How to convert C to K

+273

TEMPERATURE definition

Average kinetic energy of particles (E_k)

What happens to temperature during change of state (and why)

Remains constant (energy is used to overcome forces)

RELATIVE ATOMIC MASS (A_r) definition

Mean mass of isotopes

RELATIVE FORMULA/MOLECULAR MASS (M_r) definition

All A_rs of a coumpound added together

Simplest ratio of atoms of each element in a compound

Empirical formula

Actual number of atoms of elements in a molecule

Molecular formula

MOLECULAR FORMULA calculation

(Mr of a compound)/(Mr of its EF) = x

x * EF = MF

MOLECULAR CONCENTRATION definition

Amount of solute in a known volume of a solution

How to convert gdm-3 to moldm-3

(g dm-3) * Mr = mol dm-3

Avogadro’s law

Equal volumes of all gasses (of same temperature and pressure) contain equal numbers of moles and molecules

LIMITTING REAGENT (LR) definition

Compound in a formula with least molecules — it determines theoretical yield

LIMITTING REAGENT calculation

1. Calculate moles of reagents (of balanced equation)

2. Divide each by reaction coefficient (smaller = LR)

PERCENTAGE YIELD calculation

% = (experimental yield / theoretical yield) * 100

IDEAL GAS LAW (4 requirements)

• Particles in constant, random motion

• With negligible volume

• No intermolecular forces between them

• Ellastic collisions

When does the IDEAL GAS law actually work

At hight temperature and low pressure

3 GAS LAWs (graphs)

• P ∝ 1/V

• V ∝ T

• P ∝ T

Explain relationship between volume and pressure in a gas

Lower volume, higher particle concentration, more collisions, higher pressure

Explain relationship between temperature and volume in a gas

Higher temperature, particles have higher KE, higher collisions, higher volume

Explain relationship between temperature and pressure in a gas

Higher temperature, particles have higher KE, higher collisions with container walls, higher pressure

IDEAL GAS (word) equation with units

Pressure (Pa) x volume (m3) = moles x R (gas constant = 8.31 JK-1mol-1) x temperature (K)

GREEN CHEMISTRY definition

Principles to reduce the environmental impacts of chemistry

ATOM ECONOMY definition

Number of atoms used for useful products (amount not wasted)

ATOM ECONOMY definition

AE = ((Mr of desired product) / (total Mr of all products)) * 100

Two ways of raising the atom economy

• Decomposition

• Finding use for waste

Steps of determining the formula from combustion data

1. mass of elements = (Mr of elements / Mr of compound) * mass of compound

2. Calculate moles of elements

3. Find EF

4. Find MF

PERCENTAGE UNCERTAINTY formula

RU = (AU / value) * 100

Formula for diluting solutions

c₁v₁ = c₂v₂