Chemistry Topic 9 - Separate Chemistry II

flame test

A method of identifying a metal cation by the colour it produces in a non-luminous Bunsen flame.

How to carry out a flame test

- Dip clean nichrome wire in concentrated hydrochloric acid to avoid contamination

- Then dipped in solid sample and placed in clean blue flame

Why is Nichrome wire used in flame tests?

Because it's unreactive

Lithium ion colour (flame test)

red

Sodium ion colour (flame test)

yellow

potassium ion colour (flame test)

lilac

Calcium ion colour (flame test)

orange-red

copper ion colour (flame test)

blue-green

copper ion precipitate colour (upon adding NaOH), soluble in excess?

light blue , no

calcium ion precipitate colour (upon adding NaOH), soluble in excess?

white, no

aluminium ion precipitate colour (upon adding NaOH), soluble in excess?

white, yes

Iron(II) ion precipitate colour (upon adding NaOH), soluble in excess?

green, no

Iron(III) ion precipitate colour (upon adding NaOH), soluble in excess?

red brown, no

How to distinguish between calcium and aluminium ions

Start adding a little NaOH to solution then start increasing the NaOH added, if the precipitate dissolves then its aluminium otherwise it's calcium

Test for ammonium ions

add sodium hydroxide, warm gently, damp red litmus paper turns blue and a pungent smell is produced

Ammonium ion symbol

NH4+

NH4+ (aq) + OH- (aq)→

NH3 (g) + H2O (l)

Test for carbonate ions

1.Add dilute acid and test the gas released.

Effervescence should be seen and the gas produced is 2.CO2 which forms a white precipitate of calcium carbonate when bubbled through limewater:

CO3²⁻ (aq) + 2H+ (aq) →

CO2 (g) + H2O (l)

Test for sulfate ion (SO₄²⁻)

Add some dilute hydrochloric acid (to remove any unwanted anions such as carbonate ions) and then add some barium chloride solution. A white precipitate of barium sulfate should form.

Test for halide ions (generic)

Acidify with dilute nitric acid (HNO3) followed by the addition of silver nitrate solution (AgNO3).

Colour will vary depending on the halide

Silver chloride colour

white

Silver bromide colour

cream

Silver iodide colour

yellow

Why do we add nitric acid for halides and hydrochloric acid for sulfates?

To remove carbonate ions

Ba2+ (aq) + SO42- (aq) →

BaSO4 (s)

Advantages of instrumental methods over traditional methods

Greater accuracy

Faster and easier to use

Automated and can perform multiple simultaneous sampling and testing

Modern instruments are very sensitive and can work with multiple sample sizes

functional group

the portion of a molecule that is active in a chemical reaction and that determines the properties of many organic compounds

Displayed formula

A formula showing the relative positioning of all the atoms in a molecule and the bonds between them.

Homologous series

A series of organic compounds with the same functional group but with each successive member differing by CH2. Therefore, they have similar chemical properties and there is a trend in physical properties

molecular formula

a chemical formula of a molecular compound that shows the kinds and numbers of atoms present in a molecule of a compound

Hydrocarbons

Compounds composed of only carbon and hydrogen

Alkanes

a homologous series of saturated hydrocarbons that only contain carbon and hydrogen connected by simple bonds (no double bonds) and end in -ane, general formula: CnH2n+2

Why are alkanes considered to be saturated?

They contain no C=C double bond

methane, ethane, propane, butane (molecular formulae)

CH4, C2H6, C3H8, C4H10

Alkene

A homologous series of unsaturated carbons with a C=C double bond and end in -ene, general formula: CnH2n

What does having a C=C bond mean for alkenes?

It means they can form more bonds with other atoms by releasing their C=C double bond and each carbon atom will form 4 single bonds instead of 2 single and 1 double bond.

Ethene, propene, butene, pentene (molecular formulae)

C2H4, C3H6, C4H8, C5H10

isomers

Compounds with the same formula but different structures.

Example of isomer

but-1-ene and but-2-ene

What does but-1-ene mean?

The C=C bond is between the first 2 carbon atoms

What does but-2-ene mean?

The C=C bond is at the 2nd point between 2 carbons from the left, in other words it is between the second and third carbon.

combustion equation

Hydrocarbon + O2 --> CO2 + H2O

How to distinguish between alkanes and alkenes

Bromine water test: Shake the test tube with bromine water added to both Orange bromine water stays orange with alkanes (C-C single bonds) but becomes clear with alkenes (C=C double bonds). This is because unlike the alkane the alkene reacted with the bromine water to form a colourless product

Addition reactions of alkenes

atoms are added across the C=C double bond so that the double bond becomes a single carbon-carbon bond.

meth/eth/prop/butane + bromine goes to

1,2-dibromometh/eth/prop/butane

polymer

a substance of high average relative molecular mass made up of small repeating units called monomers

What is each monomer in a polymer called?

A repeat unit

How are monomer units connected together?

Through covalent bonds

Examples of polymers

carbohydrates, proteins, and nucleic acids(naturally occurring polymers)

plastics (synthetic polymer)

What is the process called by which monomers join to make a polymer?

Polymerisation

How does addition polymerisation of alkenes work

Double bonds break and join together with the adjacent monomer

Requirements for polymerisation reactions

high pressures

use of a catalyst

How to write out a polymer structure and a repeat unit and a monomer

For polymer:

1.Draw two C atoms that were in a double bond with a single covalent bond

2.Draw brackets and label n

3. Add the links outside the brackets

4.Add the atoms that were attached to each atom of the C bonds

For repeat unit it is the same as a polymer but without brackets or n

Monomer: put the normal molecule with a double bond in brackets preceded by n

properties of polyethene

Flexible, cheap, good electrical insulator

uses of polyethene

plastic bags, plastic bottles, wire insulation, cling film, polytunnels

properties of polypropene

Flexible, does not shatter/strong

uses of polypropene

buckets, bowls, crates, ropes, carpets

properties of polychloroethene (PVC)

tough, cheap, long lasting, good electrical insulator

Uses of polychloroethene (PVC)

window frames, gutters, water pipes insulation for electrical wires

properties of polytetrafluoroethene(PTFE)

tough and slippery

Uses of polytetrafluoroethene (PTFE)

non-stick coating for frying pans, stain-proofing clothing, carpets

condensation polymers

Polymers formed by the elimination of small molecules(mainly water) when monomers bond together.

How does condensation polymerisation work?

- each molecule has a functional group at each end

- each functional group can react with the functional group of another monomer creating long chains of alternating monomers

- for each new bond that forms, a small molecule (e.g. water) is lost

alcohol + carboxylic acid→

ester + water

how does alcohol and a carboxylic acid release water

The H from the OH and the OH from the O=COH join to make water

ester link

The O=C-O group which is found between monomers in a polymer.

How many water molecules are lost per ester link?

1

Problems with polymers - supply

Made from alkenes which are obtained from crude oil which is a finite resource so this means the price is increasing

Problems with polymers - recycling

Polymers can be recycled but different polymers must be separated from each other

This process is difficult and expensive

Problems with polymers - landfills

Waste polymers are disposed of in landfill sites but this takes up valuable land, as polymers are non-biodegradable so micro-organisms such as decomposers cannot break them down

This causes sites to quickly fill up

Problems with polymers - incineration

Polymers release a lot of heat energy when they burn and produces carbon dioxide which is a greenhouse gas that contributes to climate change

Polymers that contain chlorine such as PVC release toxic hydrogen chloride gas when burned

If incinerated by incomplete combustion, carbon monoxide will be produced which is a toxic gas

Advantage of non biodegradability

Long-lasting

Advantages of recycling polymers

1) Reduces amount of non-biodegradable items in landfills.

2) Reduces emissions of greenhouse gases.

3) Uses up less water/energy.

4) Reduces use of crude oil.

5) Saves money as polymers don't have to be made from scratch

6) Creates jobs

Disadvantages of recycling polymers

1. Sorting plastics by type of polymer is a tedious and labour intensive process which is costly

2. Recycling counts on what is collected in as the raw material, therefore production of certain types of polymers may not be possible due to a lack of starting ingredients

3. Melting polymers produces toxic gases that are harmful to plants and animals

4. Polymers can only be recycled a number of times before they lose their properties and become useless

5. Recycling runs the risk of mixing different polymers together, which again will affect their properties. This is particularly risky for polymers designed for specialist use such as aircraft or automobile parts, where safety is of utmost importance

Alcohol

a homologous series with a functional group of -OH and end in -ol. Alcohols are colourless liquids that dissolve in water to form neutral solutions.

General Formula: CnH2n+1OH

Uses of alcohols

Fuels

Solvents

Alcoholic drinks

methanol, ethanol,propanol, butanol

CH3OH

C2H5OH

C3H7OH

C4H9OH

alcohols experiment

Aim: Investigating which fuel releases the most energy

equipment : set up 100 cm3 of water in a conical flask using a support under a spirit burner for each alcohol. A thermometer should be in the water and everything should be inside a draught screen for insulation

Method: - Record initial temp and mass of water

- Heat each time until temp reaches 40 degrees, measuring time taken for each alcohol

- Then calculate the energy change by multiplying mass in grams x 4.2 x change in temperature

the highest energy change is the most effective fuel

carboxylic acid

a hoomologous series whose fucntional group is carboxyl, COOH.

Their name is alkan-oic acid

methanoic ethanoic propanoic butanoic acids formulae

HCOOH, CH3COOH,C2H5COOH,C3H7COOH

What do -oic acids go to in ion form?

-oate ion

General formula for carboxylic acids

CnH2n+1COOH

chemical properties of carboxylic acids

- react with bases to form salt and water

- react with metals to form salt and hydrogen

- soluble in water

- react with carbonates to form water co2 and salt

alcohol + oxidising agent (eg acidified potassium dichromate) =

carboxylic acid + water

All members of a homologous series have:

The same general formula

The difference in the molecular formula between one member and the next is CH2

Gradation in their physical properties

Same functional group

Similar chemical properties

fermentation reaction

Glucose (+ yeast enzymes)--> ethanol + carbon dioxide

Conditions for fermentation reaction and why

15 - 35 degrees (not too low for slow RoR and not too high for enzyme denaturation)

in the absence of oxygen (so that yeast can anaerobically respire - if it wasn't anaerobic then only CO2 and H2O would be produced)

What is the concentration of ethanol produced as a result of the fermentation reaction

15%

How to get more concentrated solution of ethanol

Fractional distillation

BP of ethanol(brutal)

78

3 types of particles based off of diameter

coarse particles(aka particulate-matter/dust)

fine particles

nanoparticles

size of nanoparticles

1-100 nm

usually contain only a few hundred atoms

diameter of fine particles

diameters of 100-2500 nm

nanoscience

the research into the production and application of nanoparticles

Is the SA:V ratio of a nanoparticle low or high?

Very high

As particle size decreases what happens to their SA:V ratio?

It increases

fullerenes

nanoparticles made of carbon

What is the main industrial application of nanoparticles and why

Inn catalysis

This is due to their high SA:V ratios and the higher the ratio then the more SA is available for reaction hence the better the catalyst

What is the nanoparticle form of titanium dioxide used in and why?

Sunscreens

This is because it blocks UV light but leaves no white marks on the skin