WEAKNESSES - practicals + mistakes

why do you need to relight the hydrogen immediately if it goes out?

to prevent hydrogen from escaping which is flammable and could cause an explosion.

what colour is copper carbonate?

green

what colour is copper oxide?

black

what are short chain alkenes used to make?

polymers

why is ethane considered a saturated compound?

• made of single carbon-carbon bonds only

• no other atoms can be added

• no addition reactions

how to collect gas in electrolysis

• fill measuring cylinder with solution/water

• place over electrode

• collect the gas by displacement of the water/solution

how to test for carboxylic acids

• add metal/carbonate

• effervescence

definition of dynamic equilibrium

• rate of the forward reaction is equal to the rate of the reverse reaction

• the concentration of the reactants and products remains constant

ethanol molecular formula

C2H6O

isotope definition

atoms with the same number of protons but different number of neutrons

compound definition

atoms of two different elements chemically bonded together

why does it take a while for the ammonium chloride ring to form

gases move in random directions and collide with the walls and themselves

why does solid sodium oxide not conduct electricity

• ions fixed in the lattice and cannot move

• no delocalised electrons

what is the colour of silver chloride

white precipitate

advantage of mixing solutions containing the same amount of moles

make sure they fully react

highest possible yield

problems caused by the disposal of addition polymers

• toxic gases when burned

• lack of space in landfill sites

why do you use pencil to draw baseline in chromatography?

insoluble

Rf calculation

solute distance

---

solvent distance

why do you heat the crucible before adding the magnesium in combustion

to clean it of impurities

what do you add into HCl for the cross disappearing experiment temperature rate of reaction thing

sodium thiosulphate

what catalyst could you add for a rate of reaction experiment

manganese oxide

copper oxide

zinc oxide

calculation for percentage of oxygen in measuring cylinder

start volume - finish volume

---

start volume x 100

what is the substance inside the double gas syringe

phosphorus

reaction of magnesium with acid

vigorous

reaction of zinc and iron with acid

slow

what also do you add to make an ester other than carboxylic and alcohol

sulfuric acid

proportion of alcohol to carboxylic acid in making esters

equal volume

what do you pour the solution over to form the ester layer

sodium carbonate solution

what is the name of the paper used for chromatography

chromatography paper

what is the name for the distance moved by the solvent

solvent front

when asked to explain the shape of a graph, what are the steps to take?

1. describe the shape e.g steepest gradient, less steep curve, curve levels off

2. explain why e.g fewer particle collisions

niche marks for explaining why magnesium chloride has a much higher melting point than hydrogen chloride (2)

• strong electrostatic attraction between oppositely charged ions

• much more energy is required to break the ionic bonds in MgCl2 than the intermolecular forces in HCl

how can the student prove manganese oxide is a catalyst and not a reactant

• filter out

• dry it

• reweigh it, should be the same mass

explain why diamond is hard but graphite is soft (5)

• diamond has a tetrahedral lattice

• every carbon atom is bonded to four other carbons

• in diamond the bonds need a lot of energy to overcome and break

• graphite is arranged in layers

• the layers can slide over each other

why does chlorine have the highest boiling point (out of the gases in the table)

chlorine has the strongest forces of attraction between its molecules

how long do you wait in a chromatography practical?

until the solvent has risen up the paper nearly to the top

correct way to write copper sulphate

copper (11) sulphate

bonding and structure of sulfur dioxide

• structure - simple molecular

• bonding - weak intermolecular forces, require little energy to overcome and break

how to physically identify a pure solid vs a mixture (3)

• measure the melting point

• if fixed melting point the substance is pure

• if melts over a range the substance is a mixture

explain how positions of chlorine, bromine and iodine depends on electronic configuration
(3)

• all in group 7

• all have 7 electrons in outer shell

• number of shells determines period they are in

if it says how a specific compound can be separated from crude oil what do you do

• describe the process of fractional distillation

• say which fraction it is and where it will leave

  • eg top of column as a refinery gas

colour copper (11) sulphate solution

blue

actual yield less than expected (3)

• spillages

• impurities

• not all reacted

soluble salt method: (8)

• heat acid

• add base and mix

• filter to obtain soluble salt solution

• heat solution

• until crystals start to form

• leave to cool

• filter out crystals

• dry crystals in a warm oven

arrangement and movement of particles in a gas

• arrangement - random arrangement, far apart

• movement - move freely, quickly

why does the lead iodide take less time to form at higher temperatures (3)

• crystals dissolve faster

• particles move faster

• particles collide after a shorter period of time

why do both isotopes have the same chemical properties

same electronic configuration

why is carbon monoxide poisonous to humans

decreases the capacity of the blood to transport oxygen

explain why the ammonium chloride ring forms closer to the hydrochloric acid end (2)

• hydrogen chloride has a higher formula mass

• hydrogen chloride diffuses slower

equation for the ammonium chloride reaction

NH3(g) + HCl(g) —> NH4Cl(s)

why could metal x be silver? (2)

• silver is less reactive than copper

• no reaction

why can octane be used as a fuel (3)

• petrol for cars

• undergoes combustion

• releases heat

method for calculating actual yield from percentage yield.(3)

• find moles of anything given in question and do ratio

• times the one you want by the Mr

• times the theoretical yield by the percentage

why could a percentage yield be greater than 100% (3)

• crystals not fully dried

• acid used more concentrated

• higher volume of acid than stated

rust chemical name

iron (111) oxide

appearance of copper metal

pink-brown/orange-brown

why is the empirical formula for the alkenes CH2 (2)

• twice as many hydrogen atoms as carbon atoms

• general formula is CnH2n

explain why the compound is an unsaturated hydrocarbon (3)

• made up of hydrogen and carbon atoms

• only

• contains C=C double bonds

complete combustion of alcohols equation

look at the sneaky O in the alcohol too

why are the spots placed above the baseline (2)

• they will not dissolve in the solvent

• the dyes can travel up the paper

incomplete combustion what state is the water produced?

liquid