Mistakes chem

How do you identify the group of an element from its ionisation energy data?

Look for a big jump in ionisation energy—this indicates a change in shell. Count backwards to find the group.

What components are required for a buffer solution?

A weak acid and its conjugate base, or a weak base and its conjugate acid.

Why are transition metal ions coloured?

Ligands cause d orbitals to split into two energy levels. Light in the visible region is absorbed to promote electrons between these levels; the remaining light is transmitted, giving the ion its colour.

Is ammonia a strong or weak base?

A weak base.

How do you find X in a formula like XH₂O?

Find moles of given mass. Calculate Mr of the whole compound. Subtract Mr of the compound without XH₂O. Divide the remainder by 18 to find X.

How do you find the oxidation state of vanadium using gas volumes?

Use gas volumes to find moles of Cl₂. 1 mole of Cl₂ = 2 electrons. Multiply moles of Cl₂ by 2 for electrons transferred. Divide by moles of vanadium to find electrons per V. Subtract from original oxidation state to get new oxidation state.

Why is a C=C bond weaker than a C–C bond?

C=C has a π and a σ bond, while C–C has two σ bonds. π bonds are weaker than σ bonds.

What is the colour change in a potassium manganate(VII) and sulfuric acid titration?

Colourless to pale pink.

Why is sulfuric acid added to the conical flask in this titration?

To provide H⁺ ions needed for the redox reaction.

What should you always remember when approaching a titration question?

Draw the titration diagram and remember that the substance in the conical flask is the one you're finding the amount of first.

What should you show in the dot-and-cross diagram of magnesium hydroxide?

Mg²⁺ with 8 electrons (full outer shell), two OH⁻ ions each with one O⁻ carrying a negative charge.

What makes an element a d-block element?

The last added electron enters a d subshell.

What does a large Kc value indicate?

The equilibrium lies to the right; products are favoured.

What happens to entropy in a system where 7 moles of product become 2 moles of reactant?

ΔS system is negative (decrease in entropy).

When can two substances with London forces mix?

When they are of similar size and have similar numbers of electrons.

Why are some substances with London forces insoluble in water?

They can't form hydrogen bonds.

Are ionic compounds soluble in water? Why?

Yes, because hydration enthalpy is greater than lattice energy.

Why are ionic compounds insoluble in non-polar solvents?

Because of strong ionic bonds that aren’t overcome by interactions with non-polar molecules.

What is the observation when magnesium nitrate is heated?

A white solid remains and it melts.

Which bond has the shortest bond length in methanol?

O-H bond.

Do you need brackets when drawing 2 repeat units of a polymer?

No, brackets aren’t needed for 2 repeat units.

Number of isomers: 1 carbon

1 isomer.

Number of isomers: 2 carbons

1 isomer.

Number of isomers: 3 carbons

1 isomer.

Number of isomers: 4 carbons

2 isomers.

Number of isomers: 5 carbons

3 isomers.

Number of isomers: 6 carbons

5 isomers.

Number of isomers: 7 carbons

9 isomers.

How many bonds in cyclohexene?

10 sigma C-H bonds, 6 sigma C-C bonds (16 sigma total), and 1 pi bond.

How to calculate increase in volume from a balanced equation?

Find total final volume and subtract the initial volume.

How many bonds does carbon form?

Carbon forms 4 bonds.

How to work out mole ratio when not given?

Use stoichiometry; if a diatomic molecule reacts with another molecule, use a 1:2 ratio.

What is it called when hydroxide ions react in ethanol?

Elimination reaction.

Why might a product not be optically active?

It forms a racemic mixture due to a planar carbocation allowing attack from both sides.

How do you know if it's an SN1 mechanism?

If there’s 1 species in the rate-determining step.

What must an alcohol be converted into before reacting with KCN in ethanol?

A halogenoalkane.

What are the steps in a Grignard reaction?

React Mg with halogenoalkane in dry ether. Add CO₂, methanal, aldehyde, or ketone. Add dilute HCl.

How to structure a 6-marker on NMR?

State number of peaks for ¹³C and ¹H NMR. Relative peak areas. Mention splitting. Add together peaks for identical environments.

What is a singlet in NMR?

A single peak; often seen when O-H does not split.

Where does Eₐₜ go on an energy profile diagram?

Before the activation energy peak.

What is on the vertical axis of an energy profile diagram?

Number of molecules with activation energy.

What does lowering the temperature do to collision and energy?

Reduces the fraction of molecules with energy ≥ activation energy.

If a reaction has a 31% yield and you are asked to find the volume of a different organic compound, what is the calculation?

Use mass / percentage yield × 100.

What should you say in bond angle questions about separation?

Electron pairs repel to maximise separation and minimise repulsion.

Why can phosphorus form PCl₅ but nitrogen cannot form NCl₅?

Phosphorus can expand its octet using the available 3d orbital; nitrogen cannot because it has no d orbitals in the n=2 energy level.

Why does fluorine form stronger dipoles compared to chlorine?

Fluorine forms larger dipoles due to its higher electronegativity, resulting in stronger dipole–dipole forces.

What is the name of the reference peak in NMR and what is its purpose?

Tetramethylsilane (TMS); it is a reference standard.

In electrophilic substitution, what should you remember about the carbocation?

Always place the positive charge on the correct carbon—usually the first carbon if two are shown.

What does retention time in gas chromatography depend on?

Retention time depends on the compound's attraction to the stationary phase. Greater attraction = longer retention time.

How does a catalyst increase the rate constant?

A catalyst provides an alternative reaction pathway with a lower activation energy. This increases the proportion of molecules with energy ≥ Ea, speeding up the reaction.

What is the unit for the gradient when calculating the rate constant k from a graph?

The unit is simply k; it depends on the order of the reaction and rate equation.

What does a very sooty flame indicate

There is a benzene ring

How can you use 24 d photo distinguish between

• forms orange ppt

• Filter off using filter paper

• Compare melting point to literature value

Why are there two different M/Z values

Presence of carbon 13 isotope

Give a test to confirm silver halide is bromide

• use conc H2SO4

• and solid silver bromide

• Gives red-orange bromine gas

Which absorption is broad and why

Very broad due to H bonding

To identify a halide ion when reacted with silver nitrate when give. Moles and mass

• work out total mr

• Take this away from mr of silver

• Then you can identify the halide ion

Why would a wooden block be lifted up

• endothermic reaction

• Wooden block is lifted so water does not freeze

Remember when doing buffer calculations

• only do reacted thing when unknown

• Otherwise continue steeps without takeing away the moles

Why would the pH of a hider barely change when a few drops of NaOH are added

• OH- reacts with H+ to form water

• This causes the weak acid dissociate to replace H+ used up

What are 2 reasons why delta s system would be positive

• More moles of product than reactant

• Change of state

What’s the atomic spectroscopy provides evidence for the existence of

Quantum shells

what’s relative mass of an electron

1/1840

How do I find the molar volume

• divide number of moles by given volume

What’s the colour at cathode

• blue

What’s colour at anode

• yellow

What’s an ionic compound

NaCl

What conducts electricity when molten and solid

• copper

When drawing hydrogen bonding what’s it important to do

• lone pair of electrons on oxygen

Why does ice have a density at 0 degreees

• 3D lattice

• Spaces in lattice

• H-binds longer than covalent

What needs to be same for enthalpy change of a reaction

• pressure and temperature

Give a reason in terms of ionisation energy why chromium can show variable oxidation numbers

• The successive ionisation energies increase

Why do solutions differ in colour

• a chnage in colour could be due to changing oxidation state or ligand

• D orbitals split causes electrons to be promoted to higher level and light energy absorbed

• Have different colour as they absorb different wavelengths of light

Is it endo or exo when a bond if formed

Exo

What’s a free radical

• species with unpaired electron

• Homolytic fission

Why would copper carbonate be added to reaction is small amounts

• to react with remaining unreacted

How are atoms in Sulfur ionised

BomBardment of electrons

Why a copper compounds hazardous

Irritants

What type of catalyst is V2O5

• heterogenous catalyst

• SO2 absorbs and bonds weakened

• SO3 desorbs from the catalytic surface

• Oxygen reacts with VO2 regenerates the V2O5 catalyst

Reactions with Fe2+ as catalyst

• 2Fe2+ + S2O82- = 2Fe3+ + 2SO42-

• 2Fe3+ + 2I- = 2Fe2+ + I2

What happens on the Fe2+ and Fe3+ reaction

• S2O82- ions are reduced by Fe2+ and I- ions

• I- ions can be oxidised by Fe3+ ions

Remember is transition metal with an ion with 2+ charge

• electrons in 4S orbital removed

Why is Fe2+ ions readily oxidised to Fe3+ ions but Mn2+ ions are not readily oxidised to Mn3+

• fe3+ is 3d5 half filled more stable then 3d6

• Mn2+ is alr 3d5 which is more stable than 3d4

What colour is formed when VO2+ and VO2+ react

Green

What type of bonds are present in transition metal ion

• dative covalent

• Covalent

Depreciation

• water ligands removed H+ from anoth type of ligand

What do we say instead of light energy

• energy in visible region

What’s a condition needed in a. Half cell

Pt elected

Why is copper (I) complex not coloured

• full d orbital

Why does an not produce H2 with HNO3

• less positive e cell value

• NO3- is a stronger reducing agent than H+

Why would iodine not be liberated

• if it’s a solid

• Equilibrium shift to right

A colour change I. Air is due to what

• oxidation

• Oxygen in air

What indicator is used for titration with sodium thiosulfate and iodine

• starch

• Blue black to colourless

Explain how hydrogen bonds arise in water and why they do not occur in hydrogen sulfide

• Delta positive hydrogen is attracted to small oxygen atom

• Silicon is too large for H bonding

Why would a blue turn to white solid

• water ligands lost form copper 2 ion

• No spillitinv of d orbitals

• No electron transitions

Why does anhydrous solid get hot when water is added to it

• bonds formed between water ligand and copper in

• Bond formation is ectothermic

Why does the solubility of hydroxides of group 2 increase down the group

• hydration enthaply is less exoteric

• Lattice enthrall y becomes less eco

Why does water react rapidly with silicon chloride but not CCl4

• - Si has energy available

• Lone pair of water to attack

• Bit carbon has no energetically available d orbitals

• Strong C-Cl bond would need to break first

• C atom surrounded by large Cl atoms

• Steric hindrance

• Water cannot get close enough to form a bond via its lone pair

• Large silicon atom will slow attack since chlorine atoms are further apart

Steric hindrance

• large groups of atoms physically block acces to a site

Suggest why sodium chloride to water gives a neutral solution but addition of sodium propanoate to water gives an alkaline solution

• NaCl dissolves to give ions that react with water

• Propagate ions react with water to give propanoic acid and OH- ions

• [H+] is less than [OH-]