chemistry past papers

isotopes are

same number of protons different number of neutrons

oxygen is more electronegative as

it has smaller atomic radius

greater nuclear charge

carbon dioxide is non polar

because it is symmetrical so the bond polarities cancel out

you can maximise the formation of product by

surrounding the flask with cold water to prevent sublimation

disproportionation is when an element is

simultaneously being oxidised and reduced

the quicker it takes for a solution to go cloudy

the faster decomposition

rate of decomposition depends

on the metal ion size and charge density

faster decomposition=

smaller radius

greater charge density

trends in boiling temperature down group 7

boiling temp increases

more electrons

more strength of london forces

more energy required to separate molecules and break intermolecular forces

solid halides form different products with concentrated sulfuric acid as

iodide is a better reducing agent as it loses electrons more easily

issues with technicians method common

mass of solid acid not accurately weighed out- use more precise balance

some acid left in beaker-rinse out beaker and add washings to volumetric flask

insufficient mixing of solution-invert the volumetric flask several times

the shape of a 2s orbital is

spherical

the difference between 2 subatomic particles in the 2s orbital

a pair of electrons in the opposite spin

a relative formula mass instead of a relative atomic mass as

salt is a giant ionic structure not a molecular structure

a relative formula mass has no mathematical units as

it is compared to 1/12th of mass of an atom of carbon-12

flame test results on solid by addition of aqueous sodium hydroxide

lilac flame-potassium ions

no flame-magnesium ion

white precipitate-magnesium

no precipitate-potassium

when atoms of metal and group 7 react together

increases in oxidation number and gains electrons to form negative ion

how trend in bond length relates to trend in bond strength down group 7

bond length increases bond strength decreases

bonding electrons increases as less energy required to break the bonds less attracted as further from nucleus

experiment to show reactivity of chlorine and iodine

solution of chlorine water and potassium iodide mixed

pale green for chlorine solution

if contains iodine turns red brown

equation: Cl2+2i-=i2+2Cl-

why does the structure of magnesium give it a high melting temperature

giant metallic structure strong electrostatic attraction between metal ions

electronegativity is the

ability of an atom to attract the shared pair of electrons in a covalent bond

trend in group 7 electronegativity

less electronegative down the group because pair of electrons in covalent bond further from nucleus with more shielding electrons

continum of bonding type means

it has two extreme bonding types (ionic and covalent) electronegativity differences between two atoms of intermediate value result in intermediate bonding

data demonstrated in a table of continum bonding type

sodium/magnesium chloride-ionic compound so conducts electricity when molten

chlorine-simple covalent structures so has melting temperatures

aluminium chloride-ionic with covalent character so has low sublimation temperature/does not conduct electricity

deduce order of increasing size of ion Br- Ca2+ Cl- K+

Ca2+ Cl- K+ have same no. of electrons

Br- has one more shell of electrons than the other ions

Cl- to K+ to Ca2+ there are more protons in the nucleus so order of increasing size of ion is Ca2+<K+<Cl-<Br-

change in acid that would reduce the volume of gas

decrease in concentration of weak acid

decrease in reaction rate=slower formation of co2

prevent loss of gas

use a pot to contain the acid and separate

replace bung and shake so substances mix

prevent significant solubility in water of co2

use gas syringe bubble co2 through nitric acid/add pinch of calcium carbonate

how does the nuclear structure and the electronic structure of group 2 affect ionisation energy

down the group ionisation energy becomes less endothermic

electrons removed from shell further from the nucleus

electrons more shielded

despite nuclear charge no of protons being greater

2nd ionisation energy more endothermic because electron is removed from the same shell and less repulsion by electrons

the changing value of the sum of the 1st and 2nd ionisation energy descend down group 2

sum of first 2 ionisation energy decrease

reactivity increases

because group 2 elements form ionic bonds

three errors of flame test account

emitted replace with absorbed

ions move up to electrons move up

is always in visible region to sometimes

different flame test shades

calcium chloride-brick red

lithium carbonate-crimson red

strontium bromide-red

sodium chloride is less soluble in menthanol than water

hydrogen bonding between water and methanol

same strength to bonding in either component on its own

hydration of Na+ and Cl-

the ionic bonding is stronger than the bonding between sodium and methanol

why is melting temperature of silicon oxide much higher than iodine even though bonding in both is covalent

silicon oxide-giant structure-contains many strong covalent bonds

iodine-only weak london forces must be broken so more energy required to break stronger bonds in silicon oxide

iron and potassium chloride both conduct electricity when molten however iron conducts electricity when solid

molten potassium chloride can conduct electricity as ions move so carry charge

in solid and molten state iron conducts as it contains delocalised electrons that move and carry charge

solid potassium chloride contains ions in solid lattice so cannot move

why group 1 carbonates are more thermally stable than group 2 carbonates

group 2 ions have large charge than group 1 ions

group 2 ions distort bonds in carbonate ion more efficiently

the C=O bond is weakened

why do isotopes have the same chemical reactions

they have the same electronic configuration

relative abundance of two isotopes can be found by

comparing no. of particles of each isotope detected in the mass spectrometer

how to make standard solution with given hydrate

dissolve solid in distilled water using glass rod

pour solution in volumetric flask use funnel

rinse beaker and transfer washings to conical flask rinse funnel and glass rod

transfer solid to volumetric flask through solid funnel

rinse container and funnel with distilled water and transfer washing

dissolve solid in less than 250cm3

make up to 250cm3

mix flask

difference between H-N-H bond angle in ammonia and amide ion

H-N-H bond angle is smaller in amide ion as amide has more lone pairs of electrons which repel the bond pairs more than one lone pair of electrons in ammonia

sodium amide is stored in oil as

reacts violently with water/oxygen

trend in values of first ionisation energy for group containing sulfur

first ionisation energy decreases down the group even if no.of protons increase

electron being removed is further from the nucleus giving more shielding from nucleus

first ionisation energy in sulfur is lower than chlorine

sulfurs nuclear charge is less by one and the electron being removed is further from the nucleus

first ionisation energy in sulfur is lower than phosphorous

electron being removed from orbital contains 2 electrons= increase in repulsion between electrons so lost easily

diamond has a higher melting point than iodine

iodine is simple molecular which molecules are held together by weak london forces

diamond is giant covalent where carbon atoms held together by strong covalent bonds

require more energy to break than intermolecular forces

feature of bonding of carbon atoms in graphite to give electrical conductor

one electron free to move within layer to carry current

carbon atoms layered so allows flow of electricity through

reaction does not react further

oxidation number does not change further

reactions of potassium chloride, bromide and iodide with conc sulfuric acid provide evidence for as you go down group 7 hydrogen halides become better reducing agents

sulfur in sulfuric acid is reduced further by hydrogen iodide than bromide/ chloride

SO2 is produced in reaction with bromide

S produced in reaction with iodine

ionic bond is

strong electrostatic attraction between oppositely charged ions

procedure to identify nitrates of lithium rubidium and strontium using the effect of heat on three solids

brown gas for lithium and strontium no brown gas for rubidium

dissolve in distilled water

add solution of sodium hydroxide

white precipitate for strontium not for lithium and rubidium

the two arrows in the first box

two electrons in the same orbital with opposite spins

arrows all pointing in the same direction in the 3p box

three electrons with same spin because in different orbitals

a covalent bond

is the electrostatic attraction of two nuclei with a shared pair of electrons

hydrazine is a good rocket fuel when reacted with hydrogen peroxide

as large quantities of gas produced from liquids and reaction is very fast

whats the difference between relative isotopic mass and relative atomic mas

relative isotopic mass refers to mass of an atom of that isotope

relative atomic mass refers to mean mass of an atom

both relative to 1/12th the mass of a c-12 atom

ions deflection

greater mass deflected less

deflected by magnetic field and detected

smaller mass deflected more

a mass spectrometer must be operated under vacuum

to prevent collisions with particles that would deflect the ions

hydrogen iodide with ammonia solution

white

smoke

HI+NH3=NH+I-

how to get potassium iodate from reaction mixture

cool reaction mixture

filter off the less soluble potassium iodate

leave to dry

show iodine ions are present in an aqueous solution

add silver nitrate solution

yellow

precipitate

what happens when an excess of dilute hydrochloric acid is added to a sample of pure solid malachite

solid malachite disappears

effervescence

green/blue solution produced

how do atoms of different elements produce different flame colours when heated

electrons move up energy levels are excited

electrons return to lower energy level

energy emitted from atom as flame colour

different energy gaps released in different elements so different colours emitted

what is periodicity

a trend of repeating physical and chemical properties with increasing atomic number

atomic radii decrease across the period

the pattern is repeated in period 3

trend in melting temperatures across elements of period 2

at the start Li-Be bonding is metallic

metallic bonding gets stronger as no.of delocalised electrons in metal atom increase

in middle of period have a giant structure of atoms

alot of energy needed to break strong covalent bond in graphite and diamond

at the end simple molecules

weak london forces between molecules

thermal decomposition of sodium nitrate and calcium nitrate

sodium nitrate- NaNO3= NaNO2+1/2O2

calcium nitrate-Ca(NO3)2= CaO+2NO2+1/2O2

thermal stability of caesium nitrate is greater than sodium nitrate

Na+ causes more distortion

has greater charge density

distorts electron clouds

a high decomposition temperature is required

strong bonds within the carbonate ion

how to compare thermal stability of two different group 2 nitrates

first one to relight glowing splint

use light meter to measure colour of gas

use gas syringe and measure rate of production of gas

bubble gas into indicator solution and record time to change colour

collection of gases over water and volume measured

same heat applied

same amount of each nitrate in separate test tube

safety keep in fume cupboard

show sulfate is present in solution of iron sulfate in water

add hydrochloric acid

then add barium chloride solution

white precipitate

how to conduct a flame test

dip nichrome wire into clean HCL acid

dip wet wire into solid and place over luminating Bunsen flame

origin of flame test colours

energy from the flame

electrons promoted to higher energy levels

electrons return to lower energy levels

light in visible region is emitted

magnesium ion does not produce a flame colour

as no emission of light in visible region

why volume of gas collected in experiment smaller

gas test before bung replaced

magnesium coated with oxide so water formed instead of hydrogen

enable collection of gas easier

arrange equipment so magnesium ribbon drops into acid after delivery tube replaced

clean the magnesium ribbon

difference in melting temperature between magnesium oxide and potassium bromide

MgO- double charged ions

KBr- single charged ions

Mg2+ is smaller than K+ in ionic radii

more energy needed to overcome electrostatic attraction in MgO than KBr

the electrical conductivity of solid potassium bromide is poor but aqueous solution of potassium bromide solution is a good electrical conductor

solid- does not conduct because ions are not free to move

in solution-conducts because ions are free to move and carry charge

graphene and graphite are good electrical conductors but not diamond

graphene-single layer of hexagons

has delocalised electrons which are mobile

graphite- has layers

each carbon bonded to 3 others

has delocalised electrons mobile between the layers

diamond-has each carbon bonded to 4 other carbons

no delocalised electrons

why is density of iron greater than graphites

iron has greater mass than carbon atoms

packed closer than carbon atoms in graphite

why is there two different values for the compressive strength in graphite

lower value= weak london forces between layers

higher value=strong covalent C-C bond within layers

predict shape and bond angle of ClO3-

trigonal pyramidal

107 degrees

three pairs of bonding electrons and one lone pair

electron pairs repel to positions of minimum repulsion

method to show how compounds produced in decomposition of potassium chlorate can be separated

use of water only as solvent

add mixture of solids to water only

filter off the undissolved potassium chlorate

explain one disadvantage of lower than 1ppm of chlorine and higher than 3ppm in chlorine

lower than 1 ppm

-HClO will be lower

-ineffective as disinfectant

higher than 3 ppm

-HCl will be higher

-irritant

ethanol is soluble in water chloroethane is insoluble

compare types of intermolecular forces

ethanol forms hydrogen bonds with water

chloroethane forms permanent dipole-dipole attractions and london forces with water