Chemistry - 90932 Flashcards
Demonstrate understanding of aspects of carbon chemistry
By which method do nonmetals and halogens bond?
Covalent bonds
Can carbon covalently bond with other carbon to form very strong bonds?
Yes (C-C is very strong)
What are carbon-containing compounds the basis of?
Organic chemistry
What are the simplest organic compounds?
Hydrocarbons (made up of only hydrogen and carbon)
Difference between molecular and structural formula?
Molecular indicates number and type of atoms in molecule. Structural indicates the arrangement of atoms, showing covalent bonds between atoms.
Define alkanes
Family of hydrocarbons that only contain hydrogen and carbon with single covalent bonds.
General formula for alkanes
CnH2n+2 (where n is 1, 2, 3 etc)
Why do the melting and boiling points of alkanes increase as the carbon-chain increases in size?
Because the chain has more mass and therefore requires more energy is required to separate the molecules.
Which alkanes are gases/liquids at room temp?
Gases: methane, ethane, propane, butane. Liquids: pentane, hexane, heptane, octane.
Where do alkanes occur naturally?
Fossil fuels. E.g natural gas (mainly methane, also ethane) and petroleum (crude oil - mixture of hydrocarbons, incl solids/liquids/gases , with up to 30 hydrocarbons in one molecule).
Fractional distillation
Fractional distillation is the separation of a mixture into its component parts, or fractions, such as in separating chemical compounds by their boiling point by heating them to a temperature at which one or more fractions of the compound will vaporise.
How does a fractionating tower work?
- Crude oil is heated above boiling point of hydrocarbons - they vaporise. 2. Vapours are cooled. 3. Largest molecules (highest boiling point) condense first and are removed. 4. Smaller molecules (lower BP) condense and are removed. 5. Smallest molecules (lowest BP) are removed as gases.
Cracking of fractions
Process by which long chain hydrocarbons are split by the breaking of C-C bonds using high temp, pressure, and/or a catalyst. Smaller alkanes and alkenes are produced (more useful).
Define alkenes
Family of hydrocarbons that contain one C=C double bond per molecule.
Why are alkenes said to be unsaturated?
Can break double bond and add further atoms to the molecule
General formula of alkenes
CnH2n
Why doesn’t methene exist?
Two carbon atoms are required to form a double bond (has one)
What are the first two alkenes, and what are their states?
Ethene and propene, both gases at room temp.
Polymers
Large molecules made up of repeating subunits
Monomers and monomer molecules
Monomer: substance composed of monomer molecules. Monomer molecules: molecule which can undergo polymerisation, thereby contributing constitutional units to the essential structure of a macromolecule.
How does an alkene become a polymer?
The double bond in an alkene is broken by heat and a catalyst and the individual molecules can then link together (polymer)
What do ethene and propene become as a result of polymerisation?
Polyethene (polythene) and polypropene (polypropylene).
Why are polymers formed from alkenes useful as plastics?
They form huge numbers of long-chain molecules. The molecules’ covalent bonds, and intermolecular attractiveness, are very strong.
Why are polymers formed from alkenes called plastics?
The polymers are easily moulded.
Are alkanes and alkenes soluble in water?
No
Do all hydrocarbons burn (combust)
Yes
What do hydrocarbons react with and release, when heated?
Oxygen, release heat and light
Will alkanes burn completely?
Yes, if sufficient oxygen is present. No soot (unburned carbon) is produced.
What does the complete combustion of any alkane product produce as the products?
Carbon dioxide has and water. E.g methane: CH4 + 2O2 -> CO2 + 2H2O
Incomplete combustion of alkanes and alkenes produces and is caused by?
Caused by insufficient oxygen, produced carbon monoxide and water. If even less O2 is present, carbon and water are formed.
What causes yellow flame?
Incomplete combustion (hot, glowing carbon)
Why are alkenes and longer-chain hydrocarbons more likely to undergo incomplete combustion?
There are more C-C bonds to be broken.
How can we distinguish between an alkane and an alkene?
Burn both in air and the yellower one is the alkene.
What are the equations for the complete and incomplete combustion of ethene?
What is the name for a family of carbon compounds that are based on the alkane chain but with an -OH group in place of one of the hydrogen atoms?
Alcohols
General formula for alcohols?
CnH2n+1OH
First two alcohols
Methanol CH3OH, and ethanol C2H5OH
What state are the first two alcohols at room temp?
Liquid
Why are the first two alcohols (methanol, ethanol) described as volatile?
Easily vaporised
What is the solubility of methanol and ethanol?
Easily soluble in water because their molecules are strongly attracted.
Why are both methanol and ethanol able to be used as fuels?
They burn in air
What is produced by complete combustion of methanol or ethanol?
Carbon dioxide and water. Blue near-invisible flame.
What is produced by incomplete combustion of methanol or ethanol?
CO and/or C, and water. Yellow flame.
Why are methanol and ethanol known as clean-buring fuels?
They have high volatility (easily evaporate), allowing complete combustion.
Methylated spirits comprises?
90% ethanol, 9.5% methanol.
What is the ‘alcohol’ in alcoholic drinks
Ethanol
Methanol is toxic to humans and can cause…?
Blindness
Equation for fermentation of glucose
C6H12O6 (enzyme in yeast) → 2CH3CH2OH + CO2
Broadly, what do plants do with CO2?
Photosynthesis removes CO2.
Respiration adds CO2 (to atmosphere).
How are humans potentially disturbing the CO2 regulation balance?
Burning fossil-fuels produces CO2
Removing forestry removes ability to remove CO2
Greenhouse effect
CO2 and other gases in the atmosphere allow heat energy from the sun to pass through but trap heat radiating from the earth (causing global warming)
Acid rain
CO2 dissolves in water to produce H2CO3 (carbonic acid).
Equation for carbonic acid reacting with calcium carbonate (erosion of limestone/marble)
CaCO3 + H2CO3 → Ca2+ + 2HCO3-
Pollution from internal combustion engines
Internal combustion uses hydrocarbons (e.g kerosine, diesel, kerosene) which burn in air. If incomplete combustion occurs, CO, soot (C), and unburned fuel escapes.
Effects of CO on humans
Bind to haemoglobin at the expense of O2. Soot can be inhaled deep into lungs, causing diseases (e.g cancer)
