5 - formulae equations and amounts

Question 1

empirical formula

Answer 1

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

Question 2

molecular formula

Answer 2

shows the actual number of atoms of each element in a molecule

Question 3

molar mass

Answer 3

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

Question 4

mole

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

avogadro constant

Answer 5

the number of atoms of 12C in exactly 12g of carbon-12

Question 6

coefficients

Answer 6

the numbers written in front of the species when balancing an equation

Question 7

spectator ions

Answer 7

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

Question 8

hydrates

Answer 8

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

Question 9

avogadros law

Answer 9

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

Question 10

molar volume

Answer 10

the volume occupied by 1 mol of any gas

Question 11

solute

Answer 11

a substance that is dissolved

Question 12

solvent

Answer 12

a substance that dissolves a solute

Question 13

solution

Answer 13

a solute dissolved in a solution

Question 14

mass concentration

Answer 14

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

Question 15

molar concentration

Answer 15

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

Question 16

standard solution

Answer 16

a solution whose concentration is accurately known

Question 17

primary standards

Answer 17

substances used to make a standard solution by weighing

Question 18

equivalence point

Answer 18

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

Question 19

end point

Answer 19

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

Question 20

meniscus

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

titre

Answer 21

the volume added from the burette during a titration

Question 22

concordant titres

Answer 22

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

Question 23

error

Answer 23

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

Question 24

accuracy

Answer 24

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

Question 25

precision

Answer 25

a measure of how close values are to each other

Question 26

random errors

Answer 26

errors caused by unpredictable variations in conditions

Question 27

systematic errors

Answer 27

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

Question 28

measurement uncertainty

Answer 28

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

Question 29

percentage uncertainty

Answer 29

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

Question 30

theoretical yield

Answer 30

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

Question 31

actual yield

Answer 31

the actual mass obtained

Question 32

percentage yield

Answer 32

is 100x the actual yield divided by the theoretical yield

Question 33

atom economy

Answer 33

the molar mass of the desired product divided by the sum of the molar masses of the products, expressed as a percentage

Question 34

displacement reaction

Answer 34

a reaction in which one element replaces another element in a compound

Question 35

precipitation reaction

Answer 35

where an insoluble solid is one of the products