chemistry error log

Why does 4-nitrophenol have a higher boiling point than 2-nitrophenol?

Compare the bromination of benzene vs. phenol (conditions and reasoning).

• both undergo electrophilic attack

• bromination of phenol is tribromination and bromination of benzene monobromination

• bromination of benzene requires a halogen carrier such as AlBr3 but phenol does not

How does the O−H absorption differ between ethanoic acid and ethanol in an IR spectrum?

ethanoic acid - very broad peak at 2500-3300

ethanol - broad smooth 3230-3550

key distinction is that ethanoic acid has a peak at 1700 due to presence of c=o

How does the OH bond in a carboxylic acid differ from the OH bond in an alcohol in terms of infrared spectroscopy

The OH bond in a carboxylic acid shows a distinct, extremely broad absorption in IR spectroscopy, generally occurring between

2500--3300cm-1

(often overlapping with C-H stretches), whereas an alcohol's OH bond appears as a strong, broad peak at a higher wavenumber, typically

3200-3600

What are the two-stage observations when adding butylamine dropwise, then in excess, to aqueous copper(II) sulfate?

• at first a light blue precipitate is formed

• when excess the precipitate redissolves to form a deep blue solution

Write the equation for the reaction of [Cu(H2​O)6​]2+ with dropwise butylamine (RNH2​). What is the role of the amine here?

[Cu(H20)6}2+ + 2CH3CH2CH2CH2NH2 —> [Cu(H20)4(OH)2 + 2CH3CH2CH2CH2NH3+

• amine acts as a base (accepts proton from water ligand)

Describe the two-stage reaction of adding butylamine to [Cu(H2​O)6​]2+ (Equations and Observations). (excess and drop wise)

dropwise : [Cu(H2​O)6​]2+ + 2CH3​CH2​CH2​CH2​NH2​→ [Cu(H2​O)4​(OH)2​] + 2CH3​CH2​CH2​CH2​NH3+​

excess : [Cu(H2​O)4​(OH)2​] + 4CH3​CH2​CH2​CH2​NH2​→ [Cu(CH3​CH2​CH2​CH2​NH2​)4​(H2​O)2​]2+ + 2OH−+ 2H2​O

explain why different alkanes in crude oil can be separated by fractional distillation?

Different alkanes have different boiling points based on their carbon chain length and molar mass

Why does the reactivity of primary halogenoalkanes increase from chloro- to iodoalkanes? (3 Marks)

• down the group the halogen atom gets larger

• distance between 2 nuclei increases so the C-X bond length increases

• the C-X bond becomes weaker and requires less energy to overcome

"Compare the rates of hydrolysis of 1-chlorobutane and 2-chloro-2-methylpropane."

• 1-chlorobutane is primary; 2-chloro-2-methylpropane is tertiary.

• Tertiary halogenoalkanes react via SN​1, while primary react via SN​2.

• The SN​1 mechanism is faster because it involves the formation of a stable tertiary carbocation.

• Inductive Effect: Mention that the three alkyl groups "push" electron density toward the positive carbon, stabilizing it (the inductive effect).

difference in drawing out the mechanism for a primary and tertiary halogenoalkane?

SN1 VS SN2

sn2 - contains a transition state

sn1 - draw two steps (halogen leaving - carbocation intermediate)

How does the classification (type) of a halogenoalkane affect its rate of reaction?

Tertiary > Secondary > Primary

• Tertiary halogenoalkanes react via the SN​1 mechanism.

• Stability: This mechanism involves a carbocation intermediate.

• Inductive Effect: Tertiary carbocations are the most stable because they have three alkyl groups that donate electron density (positive inductive effect) to reduce the charge density on the carbon atom.

Describe the stages by which a catalytic converter converts polluting gases in a car exhaust system? (3 marks)

• adsorption of gases to catalytic surface

• weakening of bonds on catalytic surface

• desorption of products from catalytic surface

What are the conditions and reactants required for the conversion of benzene to nitrobenzene?

conc. HNO3 and H2SO4 heated under reflux with 50 degrees

COnditions and reactant required for the conversion of nitrobenzene to a phenyl amine

conc HCl and Tin - heated under reflux and add NaOH at the end

What two reactions can be done to nitriles?

hydrolysed and reduction

Conditions and reactant required for the hydrolysis of a nitrile

acidic hydrolysis : dilute HCl heated under reflux to form carboxylic acid and ammonium salt

alkaline hydrolysis : NaOH and h20 heated under reflux to form sodium carboxylate salt and ammonia gas

Write a full redox equation from the half equations for following the two changes combined

MnO4- —> Mn2+

C2O4 2- —> CO2

2MnO4_ + 16H+ + 5C204 2- —> 2Mn2+ + 8H20 + 10CO2

What catalyst must be used in a catalytic converter?

Platinum catalyst

Name the reaction an alkane undergoes

free radical substitution

what is the function of catalytic converters?

Remove CO and NO and unburnt hydrocarbons from exhaust gases and turn them into CO2, N2 and H20 using platinum catalyst

How are sulphur impurities formed?

S + O2 —> SO2 when sulphur impurities are burnt

How are sulphur impurities removed from furnace waste gases in crude oil production?

Flue gas desulphurisation using CaO or CaCO3

Write out the equation for flue gas desulphurisation?

SO2 + CaO —> CaSO3

SO2 + CaCO3 —> CaSO3 + CO2

How do greenhouse gases contribute to global warming?

trap the earths radiated infrared energy in the atmosphere

Describe the alkane reactivity and explain why?

Very unreactive due to the strong C-C and C-H bonds

name the 3 steps in free radical substitution

initiation , propagation, termination

What will happen to CL2 in initiation step of free radical substitution?

• undergoes homolytic fission forming free radicals

• CL2 —> 2CL .

What does the termination step consist of in Free Radical Substitution?

Combination of two free radicals to form an alkane

(can be alkyl radicals combining)

Write out the equation for the termination step using 2 alkyl radicals.

. CH3 + . CH3 —> CH3CH3

What happens if an alkane reacts with excess Cl2​ or Br2​ in the presence of UV light? Describe the products and the name of this process.

• further substitution

• CHCl3, CH2Cl2 , CCl4)

How do you ensure a high yield of a mono-substituted product (e.g., chloromethane) during free-radical substitution?

use an excess of alkane

Define stereoisomer

Same structural formula but a different arrangement of atoms in space

What conditions and reactants are required to convert an alkene to an alkane?

• Hydrogenation - Alkene reacted with hydrogen in presence of nickel catalyst

What conditions and reactants are required to convert an alkene to a diol? (what is observed)

oxidation using acidified potassium manganate (VII) - from purple to colourless

Write out the equation of the formation of a diol from ethene

CH2=CH2 + H20 + [O] —> CH2(OH)CH2(OH)

What conditions and reactants are required to convert an alkene to an alcohol?

• hydration

• phosphoric acid catalyst

• steam

define electrophile

Electron pair acceptor

name the order of stability of carbocations

tertiary > secondary > primary

Define the "Major Product" in an electrophilic addition reaction.

The product formed via the most stable carbocation intermediate.

Predict the major product of but-1-ene + HBr.

2-bromobutane (formed via a secondary carbocation).

What is the role of the H-Br molecule in this reaction? ( electrophilic addition of alkene)

electrophile

Why is H-Br polar?

bromine is more electronegative than hydrogen which creates a dipole

Why does the addition of HBr to propene result in two different products?

Propene is an unsymmetrical alkene, so the H can bond to either C1​ or C2​, creating different carbocation intermediates.

Explain why a secondary carbocation is more stable than a primary carbocation.

It has more alkyl groups attached to the positive carbon, which exert an inductive effect, pushing electron density toward the C+ and spreading the cha

What are the conditions required for the production of a Grinard reagent

heating a halogenoalkane or haloarene with magnesium under reflux in a solvent of dry ether

Why must a Grinard be prepared in a solvent of dry ether?

cannot allow H20 to react with Grinard as it would form an unreactive alkane

What happens to a nitrile if you hydrolyse it?

It becomes a carboxylic acid

Explain why organic reactions are heated under reflux?

heating allows to increase the rate of reaction whilst avoiding organic products with low boiling points from escaping the vessel

Explain why anti-bumping granules are used when heating under reflux?

to prevent the formation of large bubbles and allow for smoother boiling

Can you seal the equipment with a bung during heating under reflux?

No, as will cause a pressure build up due to gases expanding and cause an explosion

Draw a diagram of the equipment required for heating under reflux

For simple distillation, where should the thermometer be placed?

thermometer needs to be directly opposite condensing junction as you are measuring the temperature of the gas being collected

Explain why a collection vessel may need to be placed in an ice bath when performing simple distillation

organic distillate is often volatile so ice prevents it from evaporating

Draw the diagram for the equipment required for simple distillation

What flame colour is produced when Ca2+ is used in a flame test?

Brick red

Which two metal ions produce no colour in a flame test?

Mg2+ and Be2+

What happens when you add Sr2+ to H2SO4?

thin white ppt of SrSO4

What can you observe when Mg2+ is added to NaOH?

Thick white ppt of MgOH2

what can you observe when Ba2+ is added to NaOH?

colourless solution of BaOH2

What can you observe when Mg2+ is added to H2SO4?

colourless solution of MgSo4

describe the test for carbonate ions? (CO3 2-)

• add dilute acid (HCl or HNO3)

• effervescence

• bubble the formed gas through limewater to observe white ppt of CaCO3

How can you chemically distinguish between Na2​CO3​ and NaHCO3​ using Magnesium Sulfate (MgSO4​)?

Carbonate forms a white precipitate immediately whilst hydrogen carbonate must be heated before producing white ppt.

To distinguish carbonates from hydrogencarbonates, add MgSO4​. The [...] will form a precipitate immediately, while the [...] requires [...] to form one.

Carbonate | Hydrogencarbonate | Heating.

Why does Mg(HCO3​)2​ not precipitate immediately like MgCO3​ does?

• Back: Magnesium hydrogencarbonate is soluble in water. Heating it causes it to decompose into magnesium carbonate (MgCO3​), which is insoluble (the white precipitate).

How do you test for Sulfates?

• add dilute HCl (remove carbonates) and add Barium Chloride

• observe white ppt formation of BaSO4

How do you test for NH4+ (ammonium ions)

• add sodium hydroxide and warm gently

• ammonia gas is produced

• hold damp red litmus paper over mouth of tube and it turns blue

What reagents are used to test for presence of Group 2 Cations (Mg2+, Ca2+, Sr2+, Ba2+)

NaOH and H2SO4

What do you observe when Iodine gas is present?

purple vapour

What do you observe when bromine liquid is present?

red liquid

What do you observe when Br2 gas is present?

ornage vapour

Why must you dissolve the solid in a beaker before transferring it to the 250cm³ volumetric flask?

The final volume must be exactly 250cm³ of solution. If you add 250cm³ of water to a solid, the final volume will exceed the mark.

Describe the method to prepare 250cm³ of a standard solution from a solid.

• Weighing: Weigh the solid in a weighing boat. Tip it into a beaker and re-weigh the empty boat. Subtract the two masses to find the exact mass transferred (this is the "weighing by difference" or "double zeros" method you mentioned).

• Dissolving: Add roughly 100cm³ of distilled water to the beaker. Stir with a glass rod until the solid is completely dissolved.

• Transferring: Pour the contents into a volumetric flask using a funnel.

• Rinsing: This is a huge mark-earner! Rinse the beaker, glass rod, and funnel with distilled water and add those washings into the flask. This ensures every single molecule of your solute makes it into the flask.

• Making up to the mark: Add distilled water until the bottom of the meniscus sits exactly on the graduation line.

  • Pro-tip: Use a pipette for the last few drops so you don't overshot it!

• Homogenizing: Stopper the flask and invert it several times to mix it thoroughly.

How would you find the number of atoms of H in a 6g sample of MgOh2?

Number of particles = moles x avogadros constant

6/ 58.32 =0.103

0.103 × 2 x (6.022×10 23) =1.24 × 10. 23

What do you exclude in a Kc formula?

Solids and pure liquids

what do you include in a Kp formula?

only gases

difference in electronegativities in ionic vs covalent ?

pure covalent ; equal electronegativity values

polar covalent : one atom is more electronegative than other - pulling electron density towards it creating a partial charge

ionic : large difference in electronegative es

what’s more reactive phenol or benzene?

Phenol

how do you obtain alcohol from halogenoalkane?

react with aqueous KOH ( nucleophilic substitution)

how do you obtain alkene from halogenoalkane?

heat with Ethanolic KOH

how do you obtain alkene from alcohol?

heat with H3po4/h2so4 - dehydration

convert ester to carboxylic acid?

add excess dilute Hcl and excess dilute NaOH - heat under reflux / hydrolysis

"Explain how the colour of a transition metal complex arises."

The d-orbitals split into two energy levels;

electrons absorb energy (ΔE=hf) from visible light to be promoted to a higher d-orbital,

remaining frequencies of light are transmitted as the complementary color.

Why does SiCl4​ have a higher boiling point than Cl2​?

• both experience London forces only

• SiCL4 contains more electrons than CL2, therefore stronger London forces experienced.

• more energy required to overcome stronger London forces.

What is the nature of NO2​ gas and its effect on Universal Indicator?

It is an acidic oxide. It dissolves in the water of the indicator to form an acidic solution (pH < 7), turning the indicator red/orange.

Why do Mg and Zn both form stable 2+ ions?

• there is a large jump in IE between 2nd and 3rd IE

• the 3rd electron would be removed from a new sub shell

Define amphoteric

A substance that react both as an acid or as a base

State the observations when NaOH is added dropwise to [Cr(H2​O)6​]3+, then added in excess.

Drops: Green precipitate (Cr(OH)3​(H2​O)3​).

• Excess: Redissolves to Dark Green solution ([Cr(OH)6​]3−).

How do you distinguish between [Cr(H2​O)6​]3+ and [Cr(OH)6​]3− using one reagent?

Add acid and watch as green ppt reforms from [Cr(OH)3(H20)3] due to amphoteric nature of Cr3+ (no change for Cr(H20)6]3+

define transition metal

An element that forms at least one stable ion with a partially filled d-subshell.

Explain, in terms of its electronic configuration, why Copper is classified as a transition metal, but Zinc is not. (2 marks)

• Cu forms a Cu2+ which has a partially filled 3d9 sub shell whilst Zn forms Zn2+ which has a full d sub shell.

• Define a transition metal (IUPAC/Edexcel) and explain why Sc and Zn are excluded.

An element that forms at least one stable ion with a partially filled d-subshell.

• Sc3+ is [Ar]3d0 (empty).

• Zn2+ is [Ar]3d10 (full).

Why does the precipitate formed by Fe2+ and NH3​ not redissolve in excess NH3​, unlike Cu2+?

Ammonia is not a strong enough ligand to displace OH− or H2​O ligands from Fe2+. Ligand exchange is not favorable/stable enough.

Explain why [Cu(H2​O)6​]2+ + EDTA4−→[Cu(EDTA)]2−+6H2​O is feasible.

• entropy increases as more particles (2 → 7)

• enthalpy change remains similar as 6 bonds made and 6 broken

• therefore, Gibbs free energy (ΔG=ΔH−TΔS) . since ΔS is positive then ΔG is negative = feasible

Name 4 properties of Transition metals

1 ) Variable oxidation states

2) form complex ions

3) form coloured compounds

4) have catalytic properties

General rule for the effect of pH on the redox of transition metals?

acidic conditions favour reduction : alkaline conditions favour oxidation

Which reagents/conditions are needed to oxidize Cr3+ to CrO42−​? Give the color change.

Reagents: Hydrogen peroxide (H2​O2​) and alkali (e.g., NaOH).

• Color Change: Green solution ([Cr(OH)6​]3−) → Yellow solution (CrO42−​).

• Reason: Oxidation is easier in alkaline conditions.

Why is dilute H2​SO4​ added to potassium manganate(VII) titrations?

• To provide H+ ions because reduction is favored in acidic conditions.

  • It ensures MnO4−​ is reduced to Mn2+ (Pale pink/colorless).

  • Without acid, MnO2​ (brown ppt) forms instead.

A solution absorbs light with wavelengths corresponding to red, yellow and green light.

Which ion is most likely to be in the solution?

Why is HCl never used to acidify a KMnO4​ titration?

the Cl- would be oxidised by the very strong oxidising agent MnO4- into Cl2 gas which is toxic

(titre observed would be anomalously high) - as more Mno4- required as its also oxidising cl-