Chemistry- difficult topics

Question 1

HDPEs vs. LDPEs

Question 2

Natural polymers: polysaccarides, polypeptides and dna

Question 3

Uses of exothermic and endothermic rxs (hand warmers, self-heating cans, ice pack, sherbet)

Question 4

Reactions with alcohol (with sodium, oxidation, combustion, how it is made (hydration/fermentation)

Question 5

rechargeable and non rechargeable fuel cells

Question 6

le Chatelier’s principle

Question 7

Aristosle, antoine lavosier, Dobreiner, Newlands, Mendeleev

Answer 7

aristostle: four elements, earth, fire, air, water
antoine lavosier: non-metals, metals,earths
dobreiner; grouped elements in threes, the mean of the atomic mass number of the first and third element would equal the atomic mass number of the middle element (grouped elements by chemical properties)

Question 8

Transition metals and noble gases properties

Question 9

Required practical, exothermic and endothermic rxs.

Question 10

Avogadro’s constant

Answer 10

6.02 x 10 ^23

Question 11

The empirical formula

Question 12

nano particles, coarse particles, fine particles, buckminser fullerene

Question 13

Reactivity series of metals

Answer 13

PSLCMAZINTLCSGP
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copper and below dos not reac with acid and steam
Lead and under tarnishes except gold. (Above burns)
PSL explode with acid
PSLCM fizzes in water
NTL react with warm acid or steam very slowly

Question 14

Extraction of metals

Question 15

organic acids

Answer 15

ethanoic acid- weak (salts become metal ethanoate)
sulphuric, nitric, hydrochloric acids ae strong

Question 16

Bases

Answer 16

Metal oxides (react slower and may need to react with hot water as they aren’t soluble
Metal hydroxides
Metal carbonates

Question 17

Proton transfer rx

Answer 17

Proton transfer rx. are acid-base rx.

Question 18

concentration

Answer 18

how much solute is dissolved per dm3

Question 20

Electrolysis, electrode, electrolyte definitions

Answer 20

Electrolysis, breaking ionic compounds down using electricity
Electrode- inert rod that can conduct electricity. usually graphite bc it has a high melting point and can conduct electricity but they must be replaced frequently because they can burn with ocygen at high temperatures.
Electrolyte- ionic solution that can conduct electricity, can be broken down by electroylsis.
To test if chlorine is produced at the anode, damp litmus paper will turn red in the presence of H20

Question 21

Extraction of alumnium from aluminium oxide

Answer 21

uses: aeroplanes and car bodies, pans, drink cans, window frames,
molten aluminium oxide, cryolite is added to lower the melting point of Al2O3
electrolysed at 950 degrees , lots of energy, high temp required.

Question 22

electroylsis of ionic solutions

Answer 22

in electrolysis of ionic solutions, less reactive ion will discharge
hydroxide ions will discharge if there are no halides present:
4OH- –> 2H2O + O2 + 4e-

Question 23

ionic strucutres electric conductivity

Answer 23

in a molten state, some ionic bonds are broken and the ions are no longer fixed in a 3D lattice so they can move through the strucutre to carry charge. ions are alternatively arranged

Question 24

NPK fertilisers (macronutrients)

Answer 24

salts: mixture of compounds containing nitrogen, phosphorous, potassium, Ratio of NPK value is useful so farmers can choose fertilisers with required properties.
phosphate comes from phosphate cotaining rock but it can not be used straight on the soil as it is insoluble so it can’t be absorbed by roots:
phosphate rock + nitric acid –> phosphoric acid + calcium nitrate
phosphate rock + sulfuric acid –> single superphosphate (made of calcium sulfate + calcium phosphate)
phosphate rock + phosphoric acid –> triple superphosphate (made of calcium phosphate)

potassium salts e.g. potassium chloride and potassium sulfate are mined and are soluble so they are separated from impurities and used directly.

Haber process forms ammonia which can react with nitric acid, sulfuric acid and phosphoric acid to from ammonium salts in NPK fertilisers.

nitrogen - needed for proteins in leaves and stalks
phosphorous- speeds up the growth of roots and helps fruit to ripen.
potassium- speeds up seed growth and improves resistance to disease

Question 25

Haber process

Answer 25

high temp (450 degrees) and high pressure (200atm) nylon catalyst
Nitrogen from air: air is liquefied by colling to -200 degrees and enters fractional distillation , air is compresed by high pressure pumps.
Hydrogen from natural gas: methane + steam -> hydrogen + carbon dioxide.
Ammonia is cooled and condensed and liquefied.
unreacted hydrogen and nitrogen is recycled.

Question 26

Making fertilisers in the lab

Answer 26

when amonia dissolves in water, it produces an alkalilne solution (NH4OH) so it can react with acids to produce ammonium salts through neutralisation
e.g.nitric acid + ammonia –> ammonium nitrate (which is the best nitrogenous feritiliser)
You can make a fertiliser in the lab using a titration with diluted sulfuric acid with ammonia solution.
every time 1 cm3 of acid is added, dip a glass rod into the solutiion and test a small drop on a small piece of blue litmus paper on a spotting tile. keep adding until the litmus paper turns pink. Then pour the solution into the evaporating basin.

Question 27

Lab vs industry produced

Answer 27

Lab: small quanitaties of reactants to make batch of ammonium sulfate, concentrations are dilute,titration carried out slowlly and carefully, crystals slowy crystallised and collected. material is made of glass
Industry: raw reactants in large quantities, neutralisation occurs in a fertiliser plant.
sulfuric acid is concentrated so is hazardous (could be explosions), strong steel reaction vessels that can withstand high pressures, it is heated using energy from the exothermic rx. and the air is blown up the base of the ammonium sulfate to get fertilser granules not crystals which can block nozzles of spraying equipment.

Question 28

Advantages and disadvantages of industrially manufactured fertilisers

Answer 28

Advantages: crop yields increased, food prices decreased, more land can be set aside for nature conservation and recreation, eliminates need for fields to lie fallow, eliminates need for crop rotation so it enhances land productivity.
Disadvantages: Eutrophication , fertilisers can contaminate drinking water suppies causing blue baby syndrome and can react with oxygen in the blood, reducing the ability of the blood to carry oxygen.

Question 29

john dalton

Answer 29

all matter is made of tiny hard spheres that can not be split, atoms can rearrage and combine with other atom. Atoms of the same element are identical (atoms of different elements are different).

Question 30

separating funnel, chromatography

Answer 30

separating funnel:separates immiscible liquids
chromatography: more soluble dissolved solids travel further and are more attracted to the mobile phase rather than the stationary phase. Rf is distance moved by solute/distance moved by solvent.
If the ink is submerged: it could split up or mix with the spots, dissolve or colour the solvent, it could wash off paper, the ink could run.

Question 31

crude oil fractions

Answer 31

fuel gases (calor gas)
Gasoline( petrol for cars)
Naptha (petrochemicals)
Kerosene (jet fuel)
Diesel/gas oil (fuel for diesel engines)
Residue (lubricating oil/bitumen)
lighter crude oil fractions are more useful, combust better, easily transportible.

Question 32

chemical test for water:

Answer 32

cobalt chloride paper will turn from blue to pink in the presence of water.
anhydrous copper sulfate will turn from white to blue in the presence of water.

Question 33

Earths atmosphere

Answer 33

4.6 billion years ago- volcanic activity, molten rock, lots of CO2, nitrogen, ammonia and methane, water vapour
3.8 billion years ago, earth cooled, water vapour condensed and fell as rain, filing up hollow craters in he earths crust, absorbed a lot of CO2, water vapour decreased, carbon also formed precipirates which became sediments. nitrogen is main gas
2.7 billion years ago- algae and green plants began to form and photosyhtnesise, Co2 absorbed and ocygen increase, nitrogen is main gas. CO2 trapped in dead plants and matter and compressed under high heat + pressure to form sedimentary rock like limestone. Methane and ammonia react with oxygen.
Last 200 million years- with oxygen present, more complex organisms were formed and respired, nitrogen increased due to denitrifying bacteria in the soil. Nitrogen- 78%, Oxygen-21%, water vapour, noble gases and co2 (<1%) Argon- 0.9%

Question 34

atmospheric pollutants

Answer 34

nitrogen oxides- from oxidation of air in vehicle engines, can trigger asthma and cause acid rain, use catalytic converter in cars.
carbon dioxide- complete combustion of fuel containing carbon, causes global warming, burn less fossil fuels
sulfur dioxide- sulfur impurites reacting with oxygen, can cause respiratory issues and contribute to acid rain, remove sulfur impuriteis by reacting it with calciuum oxide
carbon monoxide- incomplete combustion of fuel containing C, toxic, reduces the oxygen-carrying capacity of blood, ensure a good supply of air
particulates/soot- from incomplete combustion of fuel containing C, damages people’s lungs and causes global dimming, blackens buildings, ensure there is a good supply of air.

Question 34

stores of carbon