Forgottens / return of mistakes that haunt me

Which gas is the most ideal, and why?

Helium, because it has the smallest particles (smaller than hydrogen as a hydrogen molecule consists of two hydrogen atoms, whereas helium is monatomic), so the particles themselves take up the least volume, and the Van der Waals forces are the weakest (as with hydrogen, the charge can be distributed across two atoms, leading to id-id forces).

Water has two polar bonds - why don’t they cancel each other out, so why does water have an overall dipole?

The H-O-H bond angle is 104.5, so water is bent and not linear

If a substance cannot dissolve in water, what is the reason?

There are hydrogen bonds between the water molecules, and the energy released from the formation of hydrogen bonds between the would-be solute and the water would not be sufficient to break the existing hydrogen bonds between water molecules, so hydrogen bonds cannot form between the would-be solute molecules and the water molecules

Sodium melting point

Low!

Why are oxides of nitrogen formed in an internal combustion engine

High temperature provides enough energy to break the NN triple bond

Equation for removal of NO from exhaust gases by a catalytic converter

2NO + 2CO —> N2 + 2CO2

Name of ketone/aldehyde functional group

carbonyl

Three carbons with NH2

Propylamine

CtripleN group name

Nitrile

Aliphatic

organic molecules where the carbon atoms form straight chains, not rings

Conditions for hydrogenation

Hydrogen gas, Pt or Ni catalyst, heat

Why are alkanes generally unreactive (including towards polar reagents)

They have strong C-C bonds and strong C-H bonds, which would therefore require a lot of heat energy to break, and the difference in electronegativity between C and H is very small so the bonds have a relative lack of polarity.

4 electrophilic addition reactions for alkenes

• Hydrogen in hydrogenation (needs hydrogen gas, Pt or Ni catalyst, heat)

• Steam, phosphoric acid catalyst, 300 heat to form alcohol

• A hydrogen halide, room temp

• A halogen molecule

Does a polyalkene decolourise bromine water

No (obviously… the double bond is broken)

Structure of white phosphorus vs red phosphorus

White phosphorus is a tetrahedron - red phosphorus is a lattice made from these tetrahedra.

Two sources of atmospheric sulfur dioxide that arise from human activity

exhaust gases from internal combustion engines; coal-fired power stations

does water have a place in a Kc equation with aqueous solutions

YES!

description of aluminium powder reaction with chlorine

Aluminium glows, chlorine colour disappears, white solid formed

magnesium oxide solubility

slightly soluble

Haber process pressure

200 atm

Reasons for experimentally obtained enthalpy change being less than/different to textbook value

• Heat energy lost to the surroundings

• Density of solution not 1g/cm3

• Specific heat capacity of solution not 4.18

• Standard conditions not used

For a reversible reaction, where the forward reaction is exothermic, when you increase the temperature, do both the forward and backwards rates increase, or just the backwards rate?

both the forward and backwards rates increase (but the backwards increases more, obviously…)

Does a 400 or 500 temperature have a higher equilibrium % of NH3 in the Haber process, and why

400, as the forward reaction is exothermic

What functional groups does Na react with

Alcohol, phenol, carboxylic acid

Density and melting point of iron compared to calcium

• Density - higher as the Ar is greater and the ionic radius is smaller

• Melting point - higher as the electrostatic forces of attraction are stronger, and more electrons are delocalised

What component do you add to the circuit for two galvanic cells

Voltmeter!!

What solutions do you use for the electrolytes for galvanic cells

(metal)SO4, I MOL/DM3

Why are copper (I) salts usually colourless

All ORBITALS in the d subshell are full, so electrons cannot be promoted

When writing an equation for how H2SO4 acts as an acid, how many protons will it lose

one!! Forms HSO4-

More frequent, successful collisions?

PER UNIT TIME.

Why reuse polyethene, instead of bin it

• Save space in landfill

• Prevent eyesore

• Avoid litter

• Non-biodegradable

• Conserves non-renewable resources

• Harmful incineration products

• Harmful to wildlife

Bonding between H2O and NO3-

hydrogen

When writing an equation to show how aqueous solutions of ammonia are alkaline, what would you put with the ammonia in the reactants

water. H2O. Not H+.

Define buffer solution

a solution that resists changes in pH when small amounts of acid or base are added

What do you label the power source on an electrophoresis diagram as

DC power source (also used for electrolysis)

Explain the principles of separation by electrophoresis

• Direction travelled relates to charge

• Distance travelled relates to charge and Mr

How would you expect the enthalpy change to differ in a reaction if nitric acid was swapped with hydrochloric acid

it would be similar, as both are strong acids

Why is the enthalpy change less for neutralisation with a carboxylic acid than with HCl

carboxylic acids are weak acids, so some energy is needed to ionise

What factors affect Kc and Kp

Temperature ONLY

Kpc definition

the ratio of the concentrations of a solute in two different immiscible solvents that are in contact with each other, when equilibrium is reached, at a particular temperature

Kstab definition

the equilibrium constant for the formation of a complex ion in a solvent from its constituent ions or molecules

Kpc between y and z - which one goes on top

Y

What two things are made during fragmentation

a cation and a free radical (the cation is detected)

Magnesium + sulfuric acid?

magnesium sulfate + hydrogen

what do you need to remember when writing an equation for the behaviour of something as an acid/base

THE REVERSIBLE ARROW

Explanation - you have to identify the oxidising/reducing agent and say why - what’s the reason?

it removes/donates electrons

5 consequences of acid rain

• erosion of buildings

• Lowers pH of rivers

• Kills fish

• leaches away soil nutrients

• Leaches aluminium salts from soil

Wording for why something’s a catalyst

it is reformed

terminology to include when deducing the molecular formula from the empirical formula

EFM - empirical formula mass

What factor is important in thermal stability of group 2 carbonates/nitrates

IONIC RADIUS

Does Ecell need a sign change

yes….

what does a ligand do with its lone pair

DONATE it to form a coordinate bond

how can you confirm that a reactant is first order

draw a graph of concentration against time - if it is 1st order, the half-life will be constant

Br2 — 2Br in terms of atomisation energy

2X ATOMISATION ENERGY

Why does the bond angle change going from benzene to cyclohexane

pi bonds transformed into sigma bonds

Why do polyamides normally biodegrade more readily than polyalkenes

C-C bonds non-polar, whereas polyamides can be broken down by hydrolysis

Rate of reaction definition

change in concentration of a product or reactant per unit time

why is a step the rate determining step

the components of the step are [the same as in the rate equation]

Calcium flame colour

red

barium flame colour

green

why is it difficult to tell if thermal decomposition has taken place for MgCO3

gas is colourless, white solid becomes white solid

Cu(OH)2 ppt colour

Blue

if you want to write Cu(OH)2 instead of the whole thing, what do you HAVE TO react with the hydrated copper in the reactants, even if the reactant is NH3

OH-

How to make an benzene-ester using an acyl chloride

add the acyl chloride to phenol in NaOH

how to distinguish between methanoic acid and another carboxylic acid

tollen’s/fehlings. Methanoic acid gives a positive result with both.

Why are diazonium salts produced with phenylamine stable

positive charge is delocalised by the ring

What do you use to maintain temperature, and what do you use when handling corrosive substances (not related at all)

• thermostatically controlled water bath

• Chemically resistant gloves

VSEPR explanation for water

• 2 lone pairs and 2 bonding pairs

• So 4 regions of electron density so geometry is based on tetrahedral structure

• Molecular geometry is bent as there are only two bonding pairs

• Lone pairs repel more than bonding pairs

• So the angle is 104.5

• This allows maximum separation with minimum repulsion

Al2O3 reaction with NaOH

Al2O3 + 2NaOH + 3H2O —> 2NaAl(OH)4 - REMEMBER THE WATER

explain, using the boltzmann distribution, why adding a catalyst increases the rate of reaction

Area under the curve with an energy greater or equal to the new, lower activation energy is higher, so there is a greater proportion of particles with sufficient energy to react, which means that there are more frequent, successful collisions

Why does ethene react with electrophiles but not polyethene

Ethene pi bond is an area of high electron density

Differences in electronegativity and their corresponding types of bonding

• <0.5 - pure covalent

• 0.5 - 1.7 - polar covalent

• >1.7 - ionic

Why does SiCl4 have a low boiling point

it has a simple molecular structure, so there are weak id-id forces between molecules which require only a little heat energy to overcome

How to use initial rates to show if a reactant is 1st order

Plot a graph of rate of reaction against concentration of reactant - if the graph is a straight line through the origin, it is first order

why would you use a large excess of a reactant when experimentally determining the order of another reactant

So that the concentration of this reactant does not change significantly, so that it doesn’t affect rate

bromine gas colour

orange-BROWN

what type of isomerism dooes [Co(NH3)3(NO2)3] show

geometrical / cis-trans

Why does strontium hydroxide produce a more alkaline solution than calcium hydroxide

strontium hydroxide is more soluble than calcium hydroxide, and it is a stronger base

If you are asked to show the polarity of a bond how do you draw it

Draw in d- and d+

why does SiH4 react in air without heating, but CH4 needs to be ignited

S-H bond is weaker than the C-H bond, so it has a lower activation energy

how does silicon dioxide behave when it reacts with NaOH

Acidic behaviour

why do gases behave less ideally at high pressures

• Size and volume of molecules becomes significant

• IMFs become significant

Why do gases behave less ideally at low temperatures

• IMFs become significant

• Collisions are not elastic

nucleophile definition

lone pair donor

A transition element is an element that can form multiple stable ions with incomplete d orbitals?

ONE OR MORE STABLE IONS

do you include water in kstab equations

NO

Can enthalpy change of neutralisation be positive

NO - always negative

describe and explain the shape of a benzene ring

• Carbon atoms have trigonal planar geometry, with 120 bond angles

• Carbon atoms are sp2 hybridised

• Sigma bonds between C-C and C-H due to head-on overlap between sp2 orbitals

• Sideways overlap between p orbitals from each carbon atom above and below ring to form pi bonds

• forming a pi system with delocalised electrons

Why is a weak O-H bond a better acid

more likely to ionise and lose a proton

what type of reaction is forming an azo dye from a diazonium salt

electrophilic substitution

Equation for regeneration of the AlCl3 catalyst

AlCl4- + H+ —> AlCl3 + HCl

Colour of bromine at rtp

red-brown liquid

Why are pi bonds weaker than sigma bonds

electrons in the bond are further away from the nucleus, so there is weaker attraction between the nucleus and electrons

How does a heterogenous catalyst work

• Reactant molecules adsorb onto the surface

• Bond weakening

• Desorption of products

can octahedral complexes show cis-trans isomerism

yes

Enthalpy change of solution: when one mole of a ___ dissolves in water to an infinite dilution

SOLUTE

how can some substances have a high solubility even though their enthalpy of solution is endothermic

• large increase in entropy

• So gibbs free energy is negative

what is released at the cathode in the electrolysis of KI solution

H2 gas

What does optically active mean

able to rotate the plane of plane-polarised light

why are amides weaker bases than amines

the lone pair of electrons on the nitrogen atom is delocalised with the C=O group, which is electron withdrawing, so the lone pair is less available to accept a proton via the formation of a dative bond