Chemistry - Paper 1

atom

the smallest portion of matter made up of a nucleus and orbiting electrons/smallest particle of an element

molecule

a substance that contains 2 or more different types of atom chemically bonded together

why do noble gases not readily react?

* they have 8 electrons in their outer shell (except helium, which has 2) i.e. they have a full outer shell
* they are unreactive and do not easily form molecules, because they have a stable arrangement of electrons.

what is charge of a silver ion

1+

empirical formula

 the simplest whole-number ratio between atoms/ions in a compound

molecular formula

shows the actual number of atoms of each type of element in a molecule

explain why the melting and boiling points of substances with simple molecular structures increase, in general, with increasing relative molecular mass

* intermolecular forces get stronger
* as molecular mass increases
* so more energy needed to break the intermolecular forces
* (so boiling point increases down Group 7)

why is diamond hard and why can it not conduct electricity?

Diamond is made up of only carbon atoms, in a giant 3D lattice, where each of those atoms has a strong covalent bonds to 4 other carbon. Every one of carbon’s 4 outer electrons is involved in one of these strong covalent bonds.

Diamond is extremely hard because it is a __giant covalent structure__ with __many strong covalent bonds.__

why is graphite soft and slippery and why can it conduct electricity?

Graphite is also made of only carbon atoms, and is also a giant structure, but it is formed of layers where each carbon atom has a strong covalent bond to 3 other carbons. This means each carbon atom has one electron not involved in a covalent bond, and these electrons form a sea of delocalised electrons between the layers.

Even though it is a non-metal, graphite can conduct electricity because the delocalised electrons are free to move.

Each layer is a giant structure, with weak forces of attraction between the layers. These layers can easily slide over each other.

Graphite is soft and slippery because it has weak forces of attraction between layers. It is used as a lubricant and in pencils because it is soft and slippery.

what type of structure is C60 fullerene and why can it no conduct electricity?

C60 fullerene which is a simple molecular structure (also known as a buckyball) is also made of only carbon atoms, but it forms molecules of 60 carbon atoms. The molecule has weak intermolecular forces of attraction between them which take little energy to overcome. Hence C60 fullerene has a low melting point, and it is soft.

C60 fullerene cannot conduct electricity. Although in each molecule every carbon is only covalently bonded to 3 others and the other electrons are delocalised, these electrons cannot jump between different molecules.

trend in group 1 metals as you go down the group

* becomes softer
* more dense
* more reactive
* produces alkaline solution
* Lithium - lightly fizzing
* Sodium - fizzing, spins like a ball, turns into a ball, metls
* Potassium - fizzing, spark burnt with lilac flame, explodes, popping sound produced

metal + water =

metal oxide + hydrogen

trend in reactivity in Group 7 elements i.e. halogens

* fluorine - yellow gas - very reactive, poisonous gas
* chlorine - pale-green gas - reactive, poisonous and dense gas
* bromine - red-brown liquid - dense red-brown volatile liquid
* iodine - purple-black solid - shimmery, crystaline solid, sublimes to form a purple vapour
* melting and boiling point increases down the group
* becomes darker down the group

acid + metal

salt + hydrogen

acid + metal oxide

salt + water

acid + metal carbonate

salt + water + carbon dioxide

approximate percentages of 4 most abundant gases in dry air

* nitrogen - 78%
* oxygen - 21%
* argon - 0.9%
* carbon dioxide - 0.04%

describe the combustion of magnesium in oxygen.

* bright white light
* produces white solid
* magnesium + oxygen → magnesium oxide
* universal indicator goes blue mixed with product

describe the combustion of hydrogen in oxygen.

* squeaky pop
* hydrogen + oxygen → water
* universal indicator goes green mixed with product

describe the combustion of sulphur in oxygen.

* burns as blue flame
* white gas (gas is acidic)
* sulphur + oxygen→ sulphur dioxide (covalent bond)
* universal indicator goes red mixed with product

thermal decomposition of copper (II) carbonate word equation

copper (II) carbonate → copper (II) oxide + carbon dioxide

reactivity of metals list starting with most reactive

* potassium
* sodium
* lithium
* calcium
* magnesium
* aluminium
* zinc
* iron
* copper
* silver
* gold

common sodium, potassium and ammonium compounds are…

soluble

how can rusting of iron be prevented?

* barrier methods -
* Rust can be prevented by coating iron with barriers (paint, grease, oil, plastic) that prevent the iron from coming into contact with water and oxygen
* However, if the coatings are washed away or scratched, the iron is once again exposed to water and oxygen and will rust
* galvanising
* Iron can be prevented from rusting making use of metals higher in reactivity than iron
* **Galvanising** is a process where the iron to be protected is coated with a layer of zinc
* ZnCO3 is formed when zinc reacts with oxygen and carbon dioxide in the air and protects the iron by the barrier method
* If the coating is damaged or scratched, the iron is still protected from rusting because zinc preferentially corrodes as it is higher up the reactivity series than iron
* Compared to iron it loses its electrons more readily:



**Zn → Zn2+ + 2e–**


* The iron stays protected as it accepts the electrons released by zinc, remaining in the reduced state and thus it does not undergo oxidation
* The electrons donated by the zinc react with hydrogen ions in the water producing hydrogen gas:



**2H+ + 2e– → H2**


* Zinc therefore reacts with oxygen and water and corrodes instead of the iron


* sacrificial protection


* Galvanising is **coating the iron with a layer of zinc** in order to prevent it from rusting. However, sacrificial protection is attaching a piece of zinc to the iron object. Both methods use the same principle to work. Even if the iron is exposed to water or oxygen in the air, the water and oxygen react with zinc, as it is more reactive.

main compound present in rust

hydrated iron (III) oxide

oxidation

gain of oxygen and loss of electrons

reduction

loss of oxygen and gain of electrons

redox reaction

a reaction involving oxidation and reduction

oxidising agent

a substance that gives oxygen and removes electrons (it itself is reduced)

reducing agent

a substance that removes oxygen ang gives electrons (it itself is oxidised)

what is a source of hydrogen ions?

acids in aqueous solutions

what is a source of hydroxide ions?

alkalis in aqueous solutions

universal indicator colour (strong acid to strong alkali)

red, orange, green, blue, purple

red litmus paper colour (strong acid to strong alkali)

red, red, red, blue, blue

blue litmus paper colour (strong acid to strong alkali)

red, red, blue, blue, blue

methly orange colour (strong acid to strong alkali)

red, orange, yellow, yellow, yellow

phenolphthalein colour (strong acid to strong alkali)

colourless, colourless, colourless, pink, pink

all nitrates are…

soluble

common chlorides…

are soluble, except for lead (II) chloride and silver chloride

common sulphates…

are soluble, except for lead (II) sulphate, barium sulphate and calcium sulphate

common carbonates are…

insoluble, except for those of sodium, potassium and ammonium

common hydroxides are…

insoluble except for those of sodium, potassium and calcium (calcium hydroxide is slightly soluble)

what is an acid?

a proton donor and release H+ ions when in aqueous solution

what is a base?

a proton acceptor

alkali + acid

water + salt (AAWS)

base + acid

water + salt (BAWS)

what is an alkali?

bases that are soluble in water

what can act as bases?

* metal oxides
* metal hydroxides
* ammonia

describe an experiment to prepare a pure, dry sample of soluble salt, starting from an insoluble reactant

* acid + insoluble base; neautralisation reaction
* copper oxide + sulphuric acid
* mix the chemicals with excess of CuO (insoluble base)
* filter (to remove excess CuO)
* heat until crystals form around a glass rod when its dipped in
* leave to crystallise (as it cools, crystals will form)
* filter to obtain crystals
* dry by leaving in a warm place

test for hydrogen

* test gas with a lighted splint
* squeaky pop

test for oxygen

* test gas with a glowing splint
* splint reignites

test for carbon dioxide

* bubble the gas produced into limewater
* limewater turns cloudy

test for ammonia

* test gas with damp, red litmus paper
* red litmus goes blue
* (pungent gas NH3)

test for chlorine

* test gas with damp, blue litmus paper
* blue litmus goes red then bleaches

describe how to carry out a flame test.

* nichrome wire
* clean the wire using HCl
* dip wire into sample
* hold in roaring flame

Li+ flame colour

red

Na+ flame colour

yellow

K+ flame colour

lilac

Ca2+ flame colour

orange-red

Cu2+ flame colour

blue-green

test for NH4+

* add NaOH (sodium hydroxide solution)
* warm gently
* pungent gas
* turns damp red litmus paper blue (ammonia)

test for Cu2+, Fe2+ and Fe3+

* NaOH
* Cu2+ - blue ppt
* Fe2+ - green ppt
* Fe3+ - brown ppt

describe the halide test and results

* add nitric acid
* add acidified silver nitrate solution
* Cl- white ppt
* Br- cream ppt
* I- yellow ppt

test for SO4 2-

* add HCl
* add acidified barium chloride solution
* white ppt

test for CO3 2-

* add HCl acid
* bubble the gas formed through limewater
* limewater gas cloudy
* if CO3 2- was solid it will disappear
* fizzing

test for water

add anhydrous cp\[\[er (II) sulphate and see if white powder turns blue

test for pure sample of water

use thermometer to check if boiling point is exactly 100 degrees Celsius

what is an exothermic reaction?

a chemical reaction in which heat energy is given out

what is an endothermic reaction?

a chemical reaction in which heat is taken in

what is a catalyst

a substance that increases the rate of reaction, by providing an alternative reaction pathway with lower activation energy, but remains chemically unchanged at the end of the reaction

what is the purpose of the cotton wool plug in the neck of the flask?

* to prevent acid spitting out, as this will result in additional loss of mass

why may the loss of mass not be the same in both experiements?

* CaCO3 may have not finished reacting

effect of SA of solid on rate of reaction and why

* greater contact area between the reactions
* therefore collisions are more frequent

effect of increased concentration of a solution on rate of reaction and why

* more HCl molecules available for CaCO3 to collide with so more frequent collisions

why does the reaction gradually slow down and stop in both reactions?

* conc of HCl decreases
* collisions less frequent as less HCl

why is sulphuric acid not suitable for marble chip reaction?

* CaCO3 would react with sulphuric acid to form CaSO4 on surface of marble chips, which is insoluble, preventing any further reaction

a higher concentration means…

more particles in the same volume

hydrocarbon

* a compound of hydrogen and carbon
* only

homologous series

a family of similar molecule with:

* same chemical properties
* trend in physical properties
* same functional group
* same general formula

functional group

* the atoms and bonds that determine the chemical properties of a compound
* determines which homologous series a molecule belongs to

isomerism

two molecules that share the same molecular formula but have different displayed formulae

why is carbon monoxide poisnous?

reduces the capacity of blood to carry oxygen

describe how the industrial process of fractional distillation separates crude oil into fractions.

* crude oil is heated. most of the crude oil becomes a gas/vapour. crude oil is pumped into the bottom of the fractionating column.
* fractionating column is hottest at the bottom and coolest at the top
* bubble caps let gases rise up the fractionating column but don’t let liquids fall back down
* gases rise up the fractionating column
* each fraction is collected when it condenses

what is fuel?

a substance that, when burned, releases energy

refinery gases use

domestic heating/cooking

gasoline use

fuel for cars

kerosene use

aircraft fuel

diesel use

fuel for lorries and buses

fuel oil use

fuel for ships and power stations

bitumen use

road surfacing/roofing

how are oxides of nitrogen produced in car engines?

nitrogen and oxygen from the air react at high temperatures

why are oxides of nitrogen produced in a car engine but not in air at room temp?

* high temp in car engine
* greater fraction of particles collide with energy>=activation energy

effects of acid rain

* kill plants
* kill fish
* damage buildings

how are long chain alkanes converted to alkenes and shorter-chain alkanes by catalytic cracking?

* using a silica catalyst
* at a temperature of 650 degrees Celsius

why is cracking necessary?

* greater demand for short chained alkanes
* there is an excess of long-chained alkanes
* cracking also produces alkenes
* alkenes are used to produce (addition) polymers/plastics

how is an additional polymer formed?

by joining up many small molecules called monomers

problems in disposal or additional polymers

* inertness and inability to biodegrade - uses up land/takes up space
* production of toxic gases/greenhouse gases when burned

describe, in terms of structure and bonding, what happens when chloroethene molecules are converted into poly(chloroethene)

* one bond in the double bond breaks
* monomers/chloroethene molecules join together
* to form a long chain
* polymer contains only single bonds

state changes that occur in the formation of an addition polymer from its monomer

* monomers join up
* double bond becomes single bond
* increase in chain length

explain how the combustion of some impurities in hydrocarbon fuels results in the formation of sulphur dioxide

* sulphur is a common impurity in hydrocarbon fuels. when these fuels are burnt, this sulphur reacts with oxygen in the air and sulphur dioxide is formed.
* suphur dioxide can dissolve in rain water, in clouds, reacting with water to form an acidic solution of suphuric acid.
* power stations that burn fossil fuels contain devices in their chimneys that ‘scrub’ the gases before they are released, which means SO2 is removed