HSC Chemistry Module 6

indicator

a compound that can reversibly change color depending on pH,

neutralisation

the reaction between an acid and a base producing a salt and water

Arrhenius' theory

this theory states that acids ionise in water to give H+ ions and bases ionise to produce OH- ions, when an acid is neutralized a salt & water is produced

Lewis theory

an acid accepts electron pairs and a base donates electron pairs

Bronsted-Lowry theory

defines an acid as a proton donor, and a base as a proton acceptor

amphiprotic

a species that can either accept or donate a proton

pH

a measure of the power of hydrogen in a system

weak acid

an acid that only undergoes partial ionisation in water

weak base

a base that only undergoes partial ionisation in water

strong acid

an acid that fully ionises in water

strong base

a base that fully ionises in water

solubility rules

a set of rules used to predict whether an ionic compound will be soluble or insoluble in water

alkali

a soluble base

acid dissociation constant

Ka, the ratio of the concentrations of the dissociated and undissociated acid parts

base dissociation constant

Kb, the ratio of the concentrations of the dissociated and undissociated base parts

ionisation constant of water

Kw, the ionic ratio between H3O and OH in water

buffer solution

a solution made from a weak acid and its conjugate base that neutralizes small amounts of acids or bases added to it

buffer capacity

the amount of acid or base a buffer solution can absorb without a significant change in pH, the greatest buffer capacity with a high concentration and equal concentration of weak acid & conjugate base.

amphoteric

A substance that can act as both an acid and a base, (Ex. water dissociation of acid to form hydronium ion/ dissociation of base to form hydroxide)

acidic solution

a solution in which \[H3O+\] > \[OH-\]

titration

a measured amount of a solution of unknown concentration is added to a known volume of a second solution until the reaction between them is just complete

equivalence point

the point in a titration where the amount of titrant added is enough to completely neutralise the analyte solution and number of moles of acid and base completely react

end point

the point in a titration at which an indicator changes color

primary standard

a standard solution that has a known concentration and is prepared by the chemist

secondary standard

A solution that has been prepared in a laboratory and has been titrated against a primary standard solution

hygroscopicity

the ability to absorb water from the atmosphere

analyte

the unknown concentration but known volume of the substance being analysed

titrant

the standard being titrated against

titre

the volumes of the titrant measured in the burette

conductometry

a measurement of electrolytic conductivity to monitor a progress of chemical reaction

buffer

compound that is able to resist a change in pH when small amounts of acid or base are added.

acidic buffer

a buffer solution with a pH less than 7, made from a weak acid and it's conjugate base.

basic buffer

a buffer solution with a pH greater than 7, made from a weak base and it's conjugate acid.

buffer region

The portion of a titration curve in which the concentration of an acid is approximately equal to that of its conjugate base; pH remains relatively constant through this region

conjugate pair

two substances related to each other by the donating or accepting of a single proton

making primary standard

1. weigh solid on electronic balance in clean beaker

2. dissolve solid in distilled water, pour into clean volumetric flask, rinsing to ensure all dissolved solid is in flask

3. add sufficient distilled water so meniscus is on calibration line

monoprotic

an acid that can donate only one proton (H+ ion) per molecule (e.g., HCl)

diprotic

acid that can donate two protons (H⁺ ions) per molecule (e.g., H2SO4)

differentiating strong & weak acids

• pH probe

• electrical conductivity conductometer

• titration with a strong base (weak base will have higher equivalence point)

• magnesium strip (strong acid will have more fizzing)

enthalpy of neutralisation

enthalpy change when one mole of water is formed in a reaction between an acid and an alkali under standard conditions

universal indicator

a mixture of indicators which show different colours in solutions of different pHs

**pH range:** 1-14

phenolphthalein

indicator with **pH range:** 8.3-10

**colour change:** clear to pink/purple

bromothymol blue

indicator with **pH range:** 6-7.6

**colour change:** yellow to blue

litmus

indicator with **pH range:** 4.5-8.3

**colour change:** red to blue

methyl orange

indicator with **pH range:** 3.1-4.4

**colour change:** red to yellow

conjugate base

acid - proton(H+)

conjugate acid

base + proton (H+)