Comprehensive Chemistry Notes: From Basic Concepts to Reactions

Posted on Jun 17, 2024 in Chemistry

Chemistry Notes

Measurements

Time = s > stopwatch

Temperature = degree Celsius/ Kelvin(K) > thermometer

Mass = kg > electronic balance

Volume = cm^3/ m^3/ dm^3 > gas syringe

Common Laboratory Apparatus for Measuring Volume

Beaker/ Measuring Cylinder = approximate volume

Pipette/ Burette = exact volume

Pipette = fixed volume

Burette = varying volume

Gas Collection Methods

Downward Delivery = gases denser than air

Upward Delivery = gases less dense than air

Displacement of Water = gases that are insoluble/ slightly soluble in water

Separation Techniques

Filtration = separate insoluble solids from a liquid-solid mixture

Evaporation to Dryness = obtain soluble pure solid from an impure solution (requires heating)

Crystallisation = obtain soluble pure solid from an impure solution (does not require heating)

Simple Distillation = separate pure solvent from a solution containing solutes

Fractional Distillation = separate pure liquid from a solution of two or more miscible liquids(completely soluble in one another when mixed)

: separated according to their boiling points

Paper Chromatography = separated based on varying solubilities

States of Matter

Atomic Structure

Nucleus = neutrons and protons

Isotopes = elements that have the same atomic number + electrons, but different mass number.

Ions = when atoms lose or gain electrons (when they become electrically charged)

Anions = negatively charged ions (formed when atoms gain electrons)

Cations = positively charged ions (formed when atoms lose electrons)

Ionic Structure = Giant Lattice Structure

Covalent Structure = Intermolecular Forces

Relative Atomic Mass (Ar) = average mass of all the atoms of its isotopes present, compared to 1/12 of the mass of a carbon-12 atom.

Relative Molecular Mass (Mr) = average mass of one molecule of that element/compound compared to 1/12 of a carbon-12 atom.

Types of Reactions

Endothermic reaction = heat ENTERS the reaction, temp of reaction > temp of surrounding

Exothermic reaction = heat EXITS the reaction, temp of reaction < temp of surrounding

Speed of reaction = electronic balance/ gas syringe

Factors affecting Speed of Reaction = concentration/ particle size/ pressure/ temperature

Redox Reactions

+ – + – —> oxidation, reducing agent

S H O E

– + – + —> reduction, oxidising agent

The Periodic Table

Group 1 elements = alkali metals

• shiny + silvery + soft solids
• low density low boiling points
• down the group density increases
• down the group melting & boiling points decreases
• down the group = more reactive

Group II elements = alkaline earth metals

Group VII elements = halogens

• poor conductors of heat & electricity
• down group VII, the colour of elements gets darker
• down group VII, melting & boiling point increases
• down group VII, reactivity decreases

Group 0 = noble gases/ inert gases

• unreactive
• low melting & boiling points
• down group 0, melting & boiling points increases

Metals and Alloys

Metals

• High melting & boiling points
• malleable & ductile
• good conductors of heat & electricity
• strong and shiny
• high density

Alloys = mixture of metal + other elements

• stronger, harder & less malleable than their pure elements.

Reactivity Series

/—————–extraction by electrolysis———–/————extraction by carbon reduction———/

Extracting Iron

Iron is extracted from the iron ore called haematite containing Fe2O3

1. Haematite is added at the top of the furnace along with coke and limestone
2. Hot air is blasted into the furnace. This causes coke (carbon) to burn rapidly. > carbon + oxygen = carbon dioxide
3. The CO2 produced reacts with more coke to form carbon monoxide
4. Carbon monoxide then reduces iron in the iron ore to iron metal
5. At high temp, molten iron flows to the bottom of the furnace while the hot waste gases containing CO, CO2, and N2 escape through the top of the furnace

Limestone (calcium carbonate) = added to iron ore to remove impurities, mostly silicon dioxide

Rusting of Iron

Causes = oxygen and water

Prevention = painting, plastic coating, oiling/greasing, electroplating

Recycling of Metals

Metals are finite sources

Advantages

• Helps prolong the supply of metals
• Reduces the amount of discarded waste in landfills, saves costs of digging up huge landfills to contain waste produced
• Helps conserve natural resources (fossil fuels) consumed during the extraction of metals.
• Helps to preserve the natural environment at sites where mining of metal ores could have been carried out

Disadvantages

• $ of recycling > $ of extracting metals
• Recycling is not a lifestyle adopted by everyone
• Gives rise to environmental problems (pollution)

Air Composition

• 78% nitrogen
• 21% oxygen
• 0.97% noble gases (mostly Argon)
• 0.03% CO2

Air Pollutants

• Carbon Monoxide: forest fire/ incomplete combustion of carbon-containing substances
  • Dizziness and headache when small amounts are inhaled.
• Methane: increased agricultural activities on animal farms and paddy fields
  • (greenhouse gases which traps heat)
  • Highly flammable and may be explosive in air
  • Global warming
• Nitrogen Oxides: Lighting activities (high temp causes N & O to react)/ forest fires
  • Penetrate and damage human lung functions, causing breathing difficulties
  • Forms acid rain (low pH kills trees, plants, fishes in lakes and rivers)
  • Increases corrosion rates of buildings and monuments
• Sulfur Dioxide: Volcanic eruptions/ combustion of fossil fuels like crude oil and coal
  • Lung irritant and causes breathing difficulties
  • Forms acid rain

Fractional Distillation of Petroleum

————————–boiling point of fractions increases, more viscous————————————–

Organic Chemistry

Alkanes = saturated hydrocarbons

• can be obtained from crude oil
• insoluble in water, soluble in organic solvents
• more carbon = higher m&bp, more viscous, less flammable
• stable & unreactive
• undergo complete/incomplete combustion in excess/limited oxygen supply (respectively)
• undergoes substitution reaction with halogens (Cl) in the presence of UV lights

Alkenes = unsaturated hydrocarbons (NO SUCH THINGS AS METHENE)

• can be obtained from cracking larger hydrocarbons
• (similar to alkanes)
• undergoes addition reactions in which one of the C=C bond is broken and each C atom forms a covalent bond with H/ Br.
  • (can undergo addition polymerisation to form polymers)

> Cracking = heating larger alkanes to a high temp of about 600 d.c and passing them over a hot catalyst like aluminium oxide + silicon dioxide

• helps meet higher demands of small alkenes used to make plastic and small alkenes required in petrol.

Hydrogenation = addition reaction of alkenes with hydrogen at high temperature and in the presence of nickel catalyst

• margarine/ vegetable oil

Bromination = addition reaction of alkenes with aqueous bromine

Polymers = non-biodegradable, produces plastic gases when burnt causing air pollution, water pollution destroys aquatic life

Alcohol

• flammable and volatile

COMBUSTION: alcohols undergo combustion in excess oxygen to form CO2 and water vapour

• highly exothermic

OXIDATION: alcohols can be oxidised to form carboxylic acid

• air or other oxidising agent agents such as acidified potassium dichromate/ potassium manganate VII

Production of ethanol: fermentation of glucose using yeast

1. the enzyme in yeast breaks down the glucose to produce ethanol and carbon dioxide
2. glucose is fermented at about 37d.c
3. the enzymes in the yeast catalyse the reaction. At the end of fermentation, ethanol is obtained from the liquid mixture by fractional distillation.

Carboxylic Acid

• formed by oxidation of alcohol
• weak acids

Reaction with reactive metals = salt + hydrogen

Reaction with alkali and bases = carboxylic salt + water

Reaction with carbonates = carboxylic salt + water + carbon dioxide