SACE Stage 2 Chemistry: Topic 4

What is the equation for photosynthesis?

6CO2 + 6H2O = C6H12O6 + 6O2

What is the equation for aerobic respiration?

C6H12O6 + 6O2 = 6CO2 + 6H2O

What is the equation for complete combustion?

C6H12 + 9O2 = 6CO2 + 6H2O

What is the equation for incomplete combustion?

C6H12 + 6O2 = 6CO + 6H2O

Why does incomplete combustion occur?

There is not enough air:fuel ratio

What does incomplete combustion produce?

Carbon monoxide, soot, unburnt hydrocarbons

In regards to combustion, what happens as the length of the fuel carbon chain increases?

More oxygen is required, therefore incomplete combustion is more likley

Why is a fossil fuel non-renewable?

It is expended faster than it is produced?

What is fuel?

A substance that provides energy when combusted

How is biodiesel produced?

Transesterification

What is a biofuel?

A fuel derived from living organic matter

Why is biofuel termed carbon neutral?

The output products are offset by the growth of plants used to create the fuel

What substances are required to produce biodiesel?

Triglyceride and methanol

What catalysts are used in biodiesel production?

KOH or NaOH

Why is biodiesel prone to incomplete combustion?

It has a large carbon chain

How is bioethanol produced?

Anaerobic alcoholic fermentation

What is the equation for the production of bioethanol?

C6H12O6 = 2C2H5OH + 2CO2

What are the benefits of biofuel as opposed to fossil fuels?

Produces less soot. Offsets pollutant products. Renewable resource

What are the similarities of biofuel and fossil fuel?

H2O and CO2 are produced

What are the equations for the quantity of heat released by a reaction?

Q = m x Cp x delta T

Q = delta H x 1000 x n

What are the equations for the molar enthalpy of a reaction?

delta H = Q/1000 x n

delta H = (kJ/mol)/M

What is a galvanic cell?

A cell that produces electrical energy from spontaneous redox reactions

How is an electrical current produced from a galvanic cell?

Electron flow

What occurs at the anode in a galvanic cell?

Oxidation

What occurs at the cathode in a galvanic cell?

Reduction

What is the purpose of a salt bridge?

To balance the charges of each half cell to allow a continuous reaction

If the salt bridge solution is KNO3, what ions move into which half cell?

NO3- to the anode. K+ to the cathode

In a galvanic cell, what metal electrode is the anode?

The more reactive metal

What is a primary cell?

An unrechargable cell

What is a secondary cell?

A rechargeable cell

What is a fuel cell?

A galvanic cell with a constant input of electrode reactants

What are the benefits of a fuel cell compared with a galvanic cell?

Unlimited lifespan, no pollutants

What are the limitations of a fuel cell?

Expensive to maintain and operate

What is a flow cell?

A rechargeable fuel cell

How is a flow cell recharged?

By reversing the reaction

What is the energy conversion of a flow cell during discharge?

Chemical energy to electrical energy

What is the energy conversion of a flow cell during recharge?

Electrical energy to chemical energy

What is the movement of electrons in a flow cell?

Electrons from the anode are passed through the volt metre and into the catholyte

Why does clay become suspended in water?

The negatively charged clay particles repel each other and cannot form clumps. The suspension is too small to be filtered out

What is added in flocculation?

Al2(SO4)3

How does flocculation work?

The strongly positive Al ion attracts the negative clay particles, forming floc which can be filtered out

What substance can be used for flocculation other than Al ions?

Positive polymers

What is a soap molecule?

A carboxylate salt

What is hard water?

Water containing Ca and Mg ions

Why is hard water detrimental to soap?

The Ca or Mg ions attach to soap molecules, preventing it from being soluble in water and creating soap scum

What substance is used for ion-exchanged zeolite water softening?

Sodium aliminosilicate

What is a substance used for water softening other than a zeolite?

Sodium carbonate

How does ion-exchange zeolite work?

The Ca and Mg ions undergo cation exchange with the zeolite Na ions

Why does a soap molecule bound to Na not form soap scum?

Na salts are always soluble

What is the purpose of water disinfection?

To kill pathogens

What is the first equation for water disinfection?

Cl2 + H2O = H3O+ + Cl- + HClO

What is the product of HClO ionised in water?

H3O+ + ClO-

How does water disinfection work?

Hypochlorus acid oxidises within the pathogen

What occurs when HClO ionises?

The pH lowers

What can be done to correct the pH of water after Cl treatment?

Add a base

What happens to the water when calcium hypochlorite is added?

The pH is increased

What is the equation when calcium hypochlorite is added to water?

Ca(OCl)2 + aq = Ca2+ + 2ClO-

What is the equation of hypochlorite with water?

ClO- + H2O = HClO + OH-

What is the optimum pH of water for humans?

7.2 - 7.8

How does reverse osmosis work?

Pressure is applied to the hypertonic solution, forcing pure water through the selectively permeable membrane and overcoming the normal osmotic balance

What is the process of distillation?

Boil the water. Condense the pure water vapour

What is the limitation of distillation?

It is very energy intensive

What are the equations for atmospheric nitrogen fixation?

N2 + O2 = 2NO

2NO + O2 = 2NO2

2NO2 + H2O = HNO3 + HNO2

What are the process involved in the nitrogen cycle?

Atmospheric nitrogen fixation, nitrogen fixing bacteria, nitrifying bacteria, denitrifying bacteria

What is eutrophication caused by?

Excess fertiliser

How is nitrogen stored in plants?

Proteins

What is the structure of a silicate ion?

Tetrahedral

What is formula for a silicate ion?

SiO4(4-)

What are the charges of aluminium, silicate and oxygen?

3+, 4+, 2-

If the charge of a silicate is -2, what is the charge of the cations it can hold?

+2

What are silicate molecules more commonly termed?

Clay molecules

How are nutrients received by plants in regards to cation exchange?

Nutrients held by the silicate are in equilibrium with H+ ions in soil solution

What is the charge of nutrients?

Positive

What causes soil acidity?

Removal of plant products

Overfarming

Decomposition

What is the equation for soil acidity?

3H+ (aq) + Al3+ (soil) = 3H+ (soil) + Al3+ (aq)

What does soil acidity cause?

Aluminium toxicity

How can soil acidity be combated?

Add a base

What are the effects of soil sodicity?

Cracked, dense, water logged soil

What happens when Na ions exchange with Ca/Mg ions on the soil?

The electrostatic attraction between soil molecules decrease, causing the soil to disperse

How can soil sodicity be rectified?

By adding CaSO4

What is an addition polymer?

The adding of unsaturated monomers without the loss of water

What is a condensation polymer?

The addition of saturated monomers by eliminating a small molecule

What is a polyester?

A polymer linked by ester groups

What is a polyamide?

A polymer linked by amide groups

What are the benefits of polymers?

Cheap, can have a broad range of properties

What are the limitations of polymers?

Contain harmful chemicals, land fill

What is a thermoplastic?

A polymer with no cross linkages across chains

What is a thermosetting material?

A polymer with cross linkages across chains

What are the properties of a thermoplastic?

Softened by heating, the effect of heating is reversible

What are the properties of a thermosetting material?

The effect of heat is not reversible

What is a biopolymer?

A polymer made from renewable plant material

What are examples of materials used to make biopolymers?

Polysaccharides, proteine, triglycerides

What is the benefit of a biopolymer?

It is biodegradable

What is the only metal that is suitable for aqueous electrolysis?

Zinc

What is the charge of an anode in an electrolytic cell?

Positive

What is the charge of a cathode in an electrolytic cell?

Negative

What is an electrolytic cell?

Forced redox reactions by electricity

What are electrolytic cells primarily used for?

Metal refinement

What ions are oxidised in preference at the anode?

Less complex ions

What is the equation for the oxidation of OH ions at the anode in an electrolytic cell?

2H2O = O2 + 4H+ + 4e-