Topic 5: Formulae, equations and amounts of substance

Question 1

an empirical formula shows

Answer 1

the smallest whole-number ratio of atoms of each element in a compound

Question 2

a molecular formula shows

Answer 2

the actual number of atoms of each element in a molecule

Question 3

the molar mass is

Answer 3

the mass per mole of a substance. it has the symbol M and the units g mol-1

Question 4

a mole is

Answer 4

the amount of substance that contains the same number of particles as the number of carbon atoms in exactly 12g of the carbon-12 isotope

Question 5

the avogadro constant is

Answer 5

the number of atoms of carbon-12 in exactly 12g of carbon-12, which is 6.02 x10 (23)

Question 6

coefficients are

Answer 6

the numbers written in front of species when balancing an equation

Question 7

spectator ions are

Answer 7

the ions in an ionic compound that do not take part in a reaction

Question 8

hydrates are

Answer 8

compounds containing water of crystallisation, represented by formulae such as CuSO4 . 5H2O

Question 9

avogadro’s law states that

Answer 9

equal volumes of gases under the same conditions of temperature and pressure contain the same numbers of molecules

Question 10

molar volume is

Answer 10

the volume occupied by 1 mol of any gas

Question 11

a solute is

Answer 11

a substance that is dissolved

Question 12

a solvent is

Answer 12

a substance that dissolves a solute

Question 13

a solution is

Answer 13

a solute dissolved in a solution

Question 14

the mass concentration of a solution is

Answer 14

the mass (in g) of the solute divided by the volume of the solution

Question 15

the molar concentration of a solution is

Answer 15

the amount (in mol) of the solute divided by the volume of the solution

Question 16

a standard solution is

Answer 16

a solution whose concentration is accurately known

Question 17

primary standards are

Answer 17

substances used to make a standard solution by weighing

Question 18

the equivalence point is

Answer 18

the point at which there are exactly the right amounts of substances to complete the reaction

Question 19

the end point is

Answer 19

the point at which the indicator just changes colour. ideally, the end point should coincide with the equivalence point

Question 20

the meniscus is

Answer 20

the curving of the upper surface in a liquid in a container. the lowest horizontal part of the meniscus should be read

Question 21

the tire is

Answer 21

the volume added from the burette during a titration

Question 22

concordant titres are

Answer 22

those that are close together (usually 0.2 cm3 of each other)

Question 23

an error is

Answer 23

the difference between an experiment value and the accepted or correct value

Question 24

accuracy is

Answer 24

a measure of how close values are to the accepted or correct value

Question 25

precision is

Answer 25

a measure of how close values are to each other

Question 26

random erros are

Answer 26

errors caused by unpredictable variations in conditions

Question 27

systematic errors are

Answer 27

errors that are constant or predictable, usually because of the apparatus used

Question 28

a measurement uncertainty is

Answer 28

the potential error involved when using a piece of apparatus to make a measurement

Question 29

the percentage uncertainty in an experiment is

Answer 29

the actual measurement uncertainty multiplied by 100 and divided by the value recorded

Question 30

the theoretical yield in a reaction is

Answer 30

the maximum possible mass of a product, assuming the complete reaction and no losses

Question 31

the actual yield in a reaction is

Answer 31

the actual mass obtained

Question 32

the percentage yield is

Answer 32

100 x the actual yield divided by the theoretical yield