Amount of substance

Question 1

Avogadro constant

Answer 1

The Avogadro constant (L) is the number of atoms, molecules, ions or other chemical entities in one mole of a substance. L = 6.02 x 1023 (it’s in your data book)

Question 2

Molar concentration

Answer 2

Molar concentration is the number of moles of a solute per litre of solution. (mol dm-3)

Question 3

Concentration

Answer 3

Concentration is amount per unit volume. (usually mol dm-3 but could be g dm-3)

Question 4

Stoichiometry

Answer 4

Stoichiometry is the ratio in which reactants react and products are produced, in whole numbers.

Question 5

Law of conservation of mass

Answer 5

The Law of conservation of mass states that mass cannot be created or destroyed.

Question 6

Limiting reactants

Answer 6

Limiting reactants are reactants that restrict the amount of product that a reaction can produce. Usually (at least) one reactant will be in excess (too much) and another will be limiting.

Question 7

Empirical formula

Answer 7

The Empirical formula shows the simplest ratio of atoms of each element present in a compound.

Question 8

Molecular formula

Answer 8

The Molecular formula is the actual number of atoms of each element present in one molecule of a compound.

Question 9

Standard conditions

Answer 9

Standard conditions are 100kPa pressure and 298K temperature. (0oC = 273K)

Question 10

Titration

Answer 10

Titration is a technique used to find the concentration of an unknown solution by adding a known solution.

Question 11

Endpoint of a titration

Answer 11

The endpoint of a titration is the point at which enough of the solution from the burette has been added to react completely with the unknown solution.

Question 12

Equivalence point

Answer 12

The equivalence point of a titration is the point at which equal moles of acid and alkali are present.

Question 13

Titre

Answer 13

The titre is the amount of solution added to reach the endpoint.

Question 14

An acid

Answer 14

An acid is a substance which forms solutions with a pH of <7, and is a “proton donor” (provides H+ ions in solution in water)

Question 15

A base

Answer 15

A base is a substance which will act as a “proton acceptor” for an acid (accepts H+ ions)

Question 16

An alkali

Answer 16

An alkali is a base which dissolves in water. It gives a pH of >7.

Question 17

An indicator

Answer 17

An indicator is something that changes colour to show the progress of a chemical reaction. It is a weak acid that changes colour depending if it is in acid or alkaline conditions

Question 18

A strong acid/alkali

Answer 18

A strong acid/alkali dissociates or ionises fully in solution in water to give H+ / OH- ions.

Question 19

A weak acid/alkali

Answer 19

A weak acid/alkali dissociates or ionises partially in solution in water to give H+ / OH- ions.

Question 20

Standard solution

Answer 20

A standard solution is one of a known concentration.

Question 21

A primary standard

Answer 21

A primary standard is a substance that is suitable for making a standard solution. (high molar mass, high solubility, stable, not hygroscopic)

Question 22

Yield of a reaction

Answer 22

The Yield of a reaction is the amount of product you get from the reaction.

Question 23

Atom economy of a reaction

Answer 23

The Atom economy of a reaction is a measure of how many atoms (in terms of atomic mass) in reactants end up in your desired product.