Chemistry EOY stuff I didn't already know

What happens to atomic radius across a period?

Decreases as no. of protons increase but there is a similar level of shielding

What happens to first ionisation energy across a period?

Increases as there is similar shielding but more protons so greater nuclear attraction

Why is there a drop in ionisation energy between group 2 and 3?

Group 3 has an electron in a higher energy level so it is easier to remove than to remove group 2’s outermost electron

Why is there a drop in ionisation energy between group 5 and 6?

Group 6 has paired electrons in the p-orbital, leading to increased electron-electron repulsion, making it easier to remove an electron compared to group 5.

How does the strength of metallic bonding change as you go up the group?

Increases as there are smaller ionsand less distance between the positive ions and delocalised electrons.

What happens to a group 2 element when reacting with oxygen?

It burns with a bright white flame, leaves a white solid

Why is Barium stored in oil?

So it doesn’t react with the air

Mg + warm water → observations and products

slow reaction, no flame , produces Magnesium hydroxide and hydrogen gas

Mg + steam → observations and products

faster reaction, bright white flame, produces Magnesium oxide and hydrogen gas.

Other Group 2 metals + cold water → observations and products

produces metal hydroxide + hydrogen gas → if metal hydroxide is soluble , makes the water very alkaline

effervescence, metal dissolves, solution heats up, if M(OH)2 was insoluble forms a white precipitate

Titanium extraction 3 steps

1.TiO2 is melted and is reacted with Cl2 at 900 degrees( in the prescence of carbon!)

2. Purify TiCl4 by fractional distillation in an argon atmosphere

3. Extract Ti with Mg at 500 degrees

Why is TiCl4 fractionally distillated in an argon atmosphere?

To remove moisture from the air as TiCl4 is susceptible to hydrolysis

What is the role of Magnesium in the extraction of Titanium?

Reducing agent

What is Mg(OH)2 used for?

Medicine - for indigestion tablets as it is insoluble

What is Ca(OH)2 used for?

Used to neutralise acidic soils - partially soluble

What does F2 look like at room temp?

A pale yellow gas. → Highly reactive

What does Cl2 look like at room temp?

A greenish-yellow gas. → very reactive

What does Br2 look like at room temp?

red liquid with dense brown/orange fumes

What does I2 look like at room temp?

A shiny grey solid that sublimates to form purple vapour

What happens to Melting and boiling points down the group of Halogens?

Increase as there are more Van der Waal’s due to more electrons

What is an oxidising agent?

electron acceptor

What colour is Iodine solution?

Dark Brown

What colour is Bromine solution?

Yellowish-brown

What colour is chlorine solution?

Pale green

What is a displacement reaction

More reactive element displaces a less reactive element in a compound

Which is the most reactive out of Chlorine and Bromine and Iodine?

Chlorine then Bromine then Iodine (ability to attract a positive ion → less shielding = more reactive)

Why do we need to add Nitric acid in Silver nitrate tests for halides?

Nitric acid reacts with any carbonate impurities in the solution otherwise Ag might react with CO3 and form AG2CO3 which is a white precipitate - could be confused for a positive result for chloride ions

What happens to the strength of reducing agents as you go down the group 7?

Increases - they oxidise (lose an electron) more easily as they have more shells so more shielding etc.

What is an acid

proton donor

What is a reducing agent

electron donor

What is electron impact ionisation?

When high energy electrons are fired at the vaporised sample by an electron gun which knocks off an electron from each of the molecules in the sample

What is the 2nd step in TOF mass spectrometry

Acceleration - positive ions are accelerated by an electric field

R.A.M definition

The average weighted mass of an atom of an element relative to 1/12th the mass of a C12 atom taking into account all naturally occuring isotopes

What does the position of the equilibrium show?

The composition of the mixture

What are the conditions for the industrial hydration of ethene?

What mechanism is it?

300 - 600 degrees and 70 atm , forward reaction is exothermic ,

catalyst of conc. phosphoric acid

electrophilic addition

Why isn’t the pressure higher for the industrial hydration of ethene to produce and alcohol?

Increasing pressure increases equilibrium yield but too much pressure would lead to the unwanted polymerisation of ethene

What are the conditions of methanol from CO?

400 degrees, 50 atm , chromium + zince oxide catalysts (forward reaction is exothermic)

What does it mean if Kc is more than 1?

More of the products are being made

What does it mean if 0 < Kc < 1?

More of the reactants are being made

What is the oxidation number of Aluminium

+3

What is the oxidation number of Oxygen in Peroxides / Superoxides

-1

What are reducing agents?

electron donors (they oxidise easily and cause another species to be reduced)

What is the definition of disproportionation reactions?

where the same element from the same species is both reduced and oxidised in one reaction

What happens if I increase the pressure on a reaction where the no. of moles of gas is the same on both sides?

No change to equilibrium yield but it increases RoR

Size of positive ions vs negative ions and why

Positive ions are smaller because they have one less shell and also have more protons than electrons so there is stronger nuclear attraction

Negative ions are bigger as they have fewer protons / electron so there is weaker nuclear attraction per electron

What happens to ionic radius across the period if they all have the same elctronic structure?

Decreases due to proton : electron ratios - same shielding but more protons

Charge of H3O ion

1+

Charge of CO3 ion

2-

Charge of Ag ion

1+

What happens to metallic bonding across a period?

Gets stronger as there are more protons and more electrons but smaller sized ions are there is similar shielding

Are simple molecules soluble in water?

No - they are generally poor unless polar

Are macromolecular substance and metals soluble in water?

No

How is macromolecular conductivity when solid and when molten?

Solid - cannot conduct

Molten - Poor

Except Graphite

What is a polar covalent bond

when there is unequal distribution of electrons in a bond due to differences in electronegativity which produces a charge seperation.

Why do longer chain alkanes have a higher mp than branched/cyclic alkanes?

Longer chain alkanes have a larger surface area of contact between molecules to form vdWs

do vdW’s occur in ionic substances?

No

What kind of bonding is in NH4OH

Ionic

Is vaporisation exothermic or endothermic?

Endothermic → IMFs are overcome

What is the definition of Mean bond enthalpy?

energy needed to break a gaseous covalent bond averaged out over a range of compounds

What happens to the oxidising power of Halogens down a group and why?

Decreases - There is more shielding so harder to attract electrons

What happens to the temperature of the fractionating column as you move up it?

It decreases

How are the superheavy fractions distilled?

In a vacuum as decreasing pressure over a substance decreases its bp → this way you don’t have to increase the temperature even more as this might lead to unintentional cracking

Why do we use glass beads in our fractionating column in the lab?

Increases the surface area to give maxiumum surface area for the vapours to condense on → thermometer should be at or below the boiling point of the most volatile substance in the mixture

Where are branched and cyclic alkanes used?

in Motor fuels to give them a higher octane number

Products of thermal cracking

Mainly alkenes an sometimes Hydrogen

Products of catalytic cracking

branched and cyclic alkanes, aromatic hydrocarbons

How do we desulfurise flue gas

using a basic calsium oxide on a scrubber for a neutralisation reaction

Why is NO harmful?

it is toxic

Why is NO2 harmful?

It produces acid rain

How does the greenhouse effect work?

UV (shortwave) radiation enters the earth and reaches the earth’s surface → it is reemitted as longer wave IR radiation which is absorbed by the C=O in CO2. It’s then trapped in the atmposhere and passed onto other molecules in the air due to collisions between them

What kind of reaction is Alkenes with Br2/ Cl2 in UV light?

Free radical substitution

What is a free radical?

neutral , highly reactive species wth an unpaired electron

What is elimination?

the removal of a small molecule from organic molecules

What are uses of Halogenoalkanes?

Refrigerants, pesticides + herbicides, aerosol propellants, solvents, PTFE (teflon - non stick pans), Plastics (PVC - chloroethene), anaesthetics ( Halothane)

Alkenes bond angle + shape

120 degrees , planar

What’s special about the alkene pi bond

they have expose elctrons that are vulnerable to attack by electrophiles.

The pi bonds repel the electron pair in nearby molecules which induces a dipole

Br2 near an alkene

becomes polar and electrophilic due to the partial charges

electrophile

electron pair acceptor

why is the tertiary carbocation more stable

things are often formed on the tertiary carbocations more than the other carbocations as as the tertiary carbocation intermediate is more stable due to the positive inductive effect caused by the alkyl groups

conditions for hydration of alkenes (not industrially)

room temp initially but must warm the mixture for the hydrolysis , prescence of conc sulphuric acid catalyst

characteristics of pure PVC

rigid plastic (due to strong IMFs), electrical insulator, waterproof, unreactive with acids

what happens when you add plasticiser to PVC

weakens IMFs so it’s more flexible → can then be used electrical wire insulation and waterproof clothing

What is the test for OH- ions?

Red litmus paper turns blue ( shows alkaline)

What is the bond angle in H-C-H and C-C-O bonds in alcohols?

109.5 degrees → repel equally to minimum repulsion/maximum seperation

H-O-C bonds in alcohol bond angle

104.5 degrees → lone pairs repel more than bonding pairs …

Order of melting points ( highest first)

Carboxylic acid → alcohols → ketones → aldehydes → ethers → alkanes → alkenes

why do alcohols have a strong boiling point?

H bonds

What are the conditions needed for partial oxidation of primary alcohols and what are the products?

• prescence of potassium dichromate (VI) , alcohol in excess , dilute sulfuric acid catalyst

• warm gently and destill immediately

• Aldehyde + water!

What are the conditions needed for full oxidation of primary alcohols and what are the products?

• prescence of potassium dichromate (VI) in excess, dilute sulfuric acid

• heat under reflux + distill

• carboxylic acid + water (2[O])

What are the conditions needed for oxidation of secondary alcohols and what are the products?

• potassium dichromate solution , dilute sulphuric acis

• heat under reflux

• ketones + water

Why are tertiary alcohols not oxidised by most oxidising agents?

It would involve breaking a C-C bond

Why must fermentation be anaerobic?

so ethanol isn’t oxidised into ethanoic acid

What extra step do we have to do after producing ethanol through fermentation?

product isn’t pure so we must fractionally distillate it

What is a nucleophile?

Electron pair donor

What does the rate of nucleophilic substitution depend upon?

Strength of C-Halide bond → C-I bond is longest and therefore weakest and so it’s the fastest substitution

What does hydrolysis mean?

splitting apart molecules by reaction with water

What can you observe with methanol and sodium?

White precipitate, effervescence, sodium dissolves

What are the conditions for nucleophilic substitution for :NH3

in ethanol , heat under pressure ( in a sealed tube)

What are the conditions for nucleophilic substitution for :CN-

in ethanol, heat under reflux

What are the conditions for nucleophilic substitution for :OH-

aqueous , heat gently