research task summaries

stuff you should know

HA + M → MA + H2

HA + MCO3 → MA + CO2 +H2O

HA + MOH → MA + H2O

conjugate acid-base pairs: differ by one hydrogen. will be opposite in nature and strength. Ka x Kb = Kw = 10^-14

pKa + pKb = 14

HA + H2O → A- + H3O+

HB +H2O → B+ + OH-

Ka = [H+] [A-] / [HA}

A STRONG ACID has a pKa < -1.74

Kb = [B+] [OH-] / [BOH]

a strong base is just group one metals, or fully soluble

amphriprotic: can act as proton acceptor/donator eg. sodium hydrogen carbonate (Na+/HCO3-) or potassium dihydrogen phosphate (K+/H2PO4-)

strong acid/base: will completely ionise, single arrow. to determine % ionisation: convert pH to [H], divide by molarity, x 100

weak acid/base: incompletely ionised, will reach equilibrium when a certain number H ions released, double arrow

monoprotic acid: only one proton

diprotic eg. sulfuric acid: two stages. first stage will fully ionise, Ka = large. second stage partially, Ka = so small we ignore. if diprotic molar ratio will be 2:1 ie. half the acid molecules will be required to neutralise

triprotic eg. phosphoric (H3PO4) , boric (H3BO3): three stages, increasingly weak. Ka=multiply the three

effect of dilution on pH: strong acid, eg. 10x dilution will increase pH by one unit. for weak acids, pH will not increase as much, consider equilibrium expression

to calculate effects of dilution/mixing calculate limiting reagent/how much will be left

dissolution process is exothermic!!!

pH/conductivity curves

pH

conductivity curves: conductivity relies on free ions. used when turbid/can’t detect colour change/very dilute

aboriginal peoples: yellow clay alkaline, neutralise stomach acid, soap tree acidic and therefore supress bacteria growth

isotactic: all on one of the hydrocarbon chain

syndiotactic: pendant groups have a regular, alternating pattern

atactic: random

titration facts

primary standard: used in volumetric analysis. must be of such high purity and stability that it can be used to prepare a solution of accurately known concentration. must be:

• available in analytical grade quality, with known composition
• high molar mass (reduce error in weighing)
• chemically stable, unaffected by air when weighing
• can’t be hygroscopic (absorb water), efflorescent (release water) or deliquescent (absorb water from surroundings and dissolve in it)
• must be readily soluble in water

HCl not suitable releases fumes and loses HCl gas, sulfuric acid hygroscopic, sodium hyroxide deliquescent

secondary standards: concentrations have been determined using primary standards

conical flask: water only, burette: solution

solution placed in titration flask = whichever is easier to see endpoint

equivalence point: present in equivalent mole ratio and completely reacted. occurs at midpoint of vertical section of curve

end point: colour change

mistakes: avoidable errors

systematic errors: constant bias that can’t be eliminated. unsuitable indicator, inaccurately calibrated pipette, faulty balance

random errors: no pattern. issues with reading meniscus, judging between two scale lines, pin pointing colour change etc

indicators

acid-base indicators normally a weak organic acid or base that will dissociate in aqueous solution finding an equilibrium therefore should only add a few drops eg. methyl orange

HInd (red) +H2O → Ind (yellow) + H3O

back titration: two stage

1. reactant of unknown concentration is reacted with an excess of a reactant of known concentration
2. the amount of the second reactant (standard solution) remaining unreacted is determined via a second titration

soaps and detergents

general structure and properties of soap and detergent (anionic, cationic and non-ionic) molecules

soap: the metal salt of a fatty acid (a long chain carboxylic acid). long hydrocarbon chain with a caboxylate ion

produced via saponification: triglyceride (fat/oil) + alkali (NaOH/KOH) → glycerol + soap (Na or K salt of fatty acid)

saponification is the hydrolysis of a fat or oil in sodium/potassium hydroxide to form a fatty acid which then reacts with the sodium/potassium hydroxide to orm the salt of the fatty acid = salt

hydrocarbon chain is non-polar/hydrophobic, and is attracted to other non-polar substances through dispersion forces.

the ionic head is polar due to the presence of the carboxylate ions/hydrophilic attracted to water through ion-dipole forces and/or hydrogen bonds

as salts of weak acids, soaps are converted by mineral acids into free fatty acids:

C17H35COONa + HCl → C17H35COOH (s) +NaCl

produce scum, therefore ineffective

detergents: have a long hydrocarbon chain, but at the end of the molecule there is a different group such as -SO3-Na+ (instead of the -COO-Na+ group in soap)

originally created in response to lack of fats during ww1.

unlike soaps, detergents are suitable for use in hard water. hard water contains concentrations of Ca and Mg between 20-180 ppm. calcium and magnesium ions bond with the carboxylate ions of soap to form a solid precipitate known as scum. this reduces number of soap ions available to form micelles, reducing effectiveness of soap as a cleaning agent.

2RCOO- + Mg2+ → (RCOO)2Mg (s)

detergents don’t form scum as their calcium/magnesium salts are more water soluble. however effectiveness is still reduced

Four main types:

• anionic: like soaps, have a negatively charged hydrophilic polar head eg. SO3-. most widely used in high foaming cleaning products such as laundry powders and shampoos. suitable for hard water.
• cationic: have a positively charged hydrophilic polar head eg. a positively charged alkyl ammonium ion. positive attracts to negatively charged substrates like hair/fabrics. hydrocarbon tails gives substrate a slippery feel, so they are used as selective conditioning agents, but not for surface cleaning. also function as germicides, as ammonium ions disrupt the cell walls of some pathogens
• non-ionic: do not have a negatively or positively charged head, rather a functional group like a hydroxyl or carboxylic acid as their hydrophilic polar head. used for cleaning where sudsing would interfere with machine function.
• zwitterionic/amphoteric: have a hydrophilic head consisting of both cationic and anionic centres in equal amounts = zero net charge

the mode of action and uses of soaps and detergents

for the cleaning processes, surface tension of water must be reduced so it spreads out and wets the surface to be cleaned. surfactants break apart H-bonding between water molecules.

soaps/detergents are emulsifiers as the non-polar, hydrophobic tail is miscible with grease allowing it to be carried by water

micelle = hydrophobic tails group together away from the polar water molecules. hydrophilic heads face outwards and are surrounded by water molecules

• soap molecules surround dirt/grease on a surface, with tails embedded into grease
• hydrophilic heads bond with surrounding water with ion-dipole forces
• when agitated, water molecules pull on the soap molecule through the ion-dipole which lifts the grease/dirt away from the surface, allowing more soap molecules to surround the dirt = micelle
• each micelle is surrounded by negatively charged heads so they repell each other/don’t aggregate. due to their small size, micelles remain suspended in the water forming an emulsion and do not resettle.
• when wash water is drained, micelles are drained as well
• amphipathic

societal impact

• reduced spread of infection
• can dry and irritate skin
• early detergents contaoned phosphate, causing eutrophication/algal blooms
• early detergents produced long lasting foam
• detergents take a long time to biodegrade

addition polymers

the monomers, structures quality, properties and uses of the following addtion polymers:

polymers: long chain macromolecules formed when many smaller monomers join by covalent bonds

monomer: a low molecular weight molecules that is capable of forming at least two covalent bonds, one with each neighbouring molecule

many polymers are carbon based due to fact carbon is able to form strongly bonded straight and branched chains

addition polymerisation:

each monomer must include a double or triple bonded carbon (unsaturated) as this is site of reaction. the polymer backbone will only contain carbon. during polymerisation there is no loss of any atom/byproducts produced. therefore addition poymers can be recognised by noting that the polymer has the same empirical formula as the monomer, but

a higher molecular mass

strucuture of polymer molecules and intra and intermolecular bonding alther the properties

thermoplastics: contain hydrogen, dipole-dipole or dispersion forces between chains. when heated, these are overcome and polymers soften. don’t burn as strong covalent bonds remain between carbon molecules eg. cling wrap, plastic shopping bags

thermoset: bonds between polymers are strong covalent. can decompose/burn. eg. bowling balls, saucepan handles, light switches

elastomers: occasional cross links. can stretch but return to original shape eg. tyres

polyethylene (PE)

non-polar C-H and C-C covalent bonds = non-polar polymer molecule. strong C-C and C-H bonds = no free electrons. only cross-linked polyethylene thermoset. Cross-linking the polyethylene also enhances the chemical and oil resistance at elevated temperatures eg. saucepan handle

polyvinyl chloride (PVC)

monomer = vinyl chloride (common name) or chloroethane (systematic name)

produces randomly orientated chlorine molecules along the chain. high degree of branching = amorphous, although unusually rigid. this is because chlorine is highly electronegative, so creates a polar C+-Cl- bond. these dipole-dipole forces add to dispersion forces between chains, holding polymer chains together strongly. large Cl atom also restricts ability of chain to ‘flop’ = rigid

plasticisers: small molecules inserted between polymer chains to hold them further apart/weaken intermolecular forces between chains. more plasticiser = more flexible. plasticised PVC is difficult to recycle because when heated, the plasticiser decomposes into compounds that destroy polymer structure

heat stabilisers and uv inhibitors can also be added to make heat/uv resistant

polystyrene (PS)

ethenyl benzene.benzene ring orientated randomly along the chain. mainly amorphous due to the way the rings stick out from the chain and their large size. dispersion forces only forces between chains, strengthened by the bulky C6H5 group. also prevent chain ‘flopping’ = chain stiffening. generally clear, rigid and brittle, readily softened/moulded when heated.

syndiotactic polystyrene far stronger, but more brittle. more expensive than atactic polystrene.

polytetrafluoroethylene/teflon (PTFE)

similar to polyethylene, except with fluorine atoms in place of ALL hydrogen atoms.

condensation polymers

condensation polymerisation: occurs with the elimination of a small molecule such as H2O or HCl, and the creation of a new functional group

due to loss of a small molecule, monomer and polymer have different chemical and empirical formulae

polymer backbone has atoms other than carbon, and must contain two functional groups

the monomers, structures, properties and uses of the following condensation polymers:

nylon 6,6 (polyhexamethylene adipamide)

hexanedioic acid/adipic acid + 1, 6 hexamethylene diamine/hexanediamine form amide linkages. n is the total number of each of the two monomers in the polymer, 2n-1 is the number of water molecules released. not biodegradable even though structure similar to natural polymers. difficult to recycle, when heated forms hazardous smoke eg. containing nitrous oxide.

polyethylene terephthalate (PET)

ethane 1,2 diol + bezene 1,4 diocacid OR dicarboxylic acid (carboxylic acid with benzene ring) + diol form ester linkages. water is eliminated due to reaction between OH of carboxylic acid and H atom on the alcohol. non biodegradable, easily recycled due to low softening temperature.

problem solving skills

6.2.2, 6.2.4, 6.2.6, 6.3.2

practical solution making/titration skills

6.3.1, 6.3.6, 6.4, 6.5