Topic 5: Formulae, Equations & Amounts of Substance

Question 1

Define : mole

Answer 1

A mole is the amount of a substance that contains the same number of carbon atoms in exactly 12g of the carbon-12 isotope

Question 2

What is Avogadro’s constant

Answer 2

Number of atoms of carbon-12 in exactly 12g of carbon-12
(6.02 x10^23)

Question 3

What is the molar mass? (M)

Answer 3

The mass per mole of the substance in g mol-1

Question 4

What is the empirical formula?

Answer 4

Smallest whole number ratio of the atoms of each element in a compound

Question 5

What is the molecular formula?

Answer 5

The actual number of atoms of each element present in a compound

Question 6

When do you use the ideal gas equation instead of the molar volume triangle?

Answer 6

When the gas isn’t at room temp and pressure

Question 7

Define net ionic equation

Answer 7

A simplified ionic equation that shows only the species involved in the chemical reaction

Question 8

What does the big N in the avogadro triangle stand for

Answer 8

Number of particles
Once you calculate this if it asks for number of atoms/ ions , multiply by the amount of species present eg. C2H4 is 2+ 4 = 6 so x6

Question 9

What is the molar volume

Answer 9

The volume of gas that contains one mole of that gas
at room temp and pressure one mole of gas will occupy 24dm^3

Question 10

Define: solute

Answer 10

A substance that is dissolved

Question 11

Define solvent

Answer 11

A substance that dissolves a solute

Question 12

Define solution

Answer 12

A solute dissolved in a solvent

Question 13

Primary standards will ideally be…

Answer 13

Chemically stable
Not absorb or react easily with substances in the atmosphere
Be soluble in water
React quickly and steadily with other solutions
Be inexpensive
Have a high degree of purity
Solids with a high molar mass

Question 14

Describe the steps in making a standard solution

Answer 14

Find the mass of solute needed
Add approximate mass of suite to weighing boat and transfer as much as possible to the beaker
Reweigh the weighing boat to improve accuracy
Calculate the actual mass of solute
Add deionised water to beaker and dissolve solute using a stirring rod
Wash the stirring rod with distilled water over the beaker to catch traces
Place the funnel into the volumetric flask and pour in solution
Rinse the beaker over the funnel with distilled water, catching rinsings in the flask
Add deionised water to the graduation mark on the flask
Add stopper and invert multiple times to mix

Question 15

What is an error

Answer 15

Something that affects results, which was not plausible to avoid or account for (given the conditions of the experiment)
Therefore accounts for the difference between an experimental value and the correct value

Question 16

What is a mistake

Answer 16

Something that affects the results, which should reasonably been avoided

Question 17

Define accuracy

Answer 17

A measure of how close the values are to the accepted/correct value

Question 18

Define precision

Answer 18

A measure of how close the values are to each other

Question 19

Define random error

Answer 19

Errors caused by unpredictable variations in conditions

Question 20

Define systematic error

Answer 20

Errors are constant and predictable, usually due to the apparatus being used

Question 21

Define measurement uncertainty

Answer 21

The potential error involved when using a piece of apparatus

Question 22

Define theoretical yield

Answer 22

The maximum possible mass of a product in a reaction assuming a complete reaction and no losses

Question 23

Define actual yield

Answer 23

The actual mass of a product obtained in a reaction

Question 24

Why is it very rare to get 100% yield

Answer 24

Reaction may be at equilibrium and therefore never reach completion
Side reactions could occur producing by-products
Impure reactants
Reactants or products left behind in previous apparatus

Question 25

Why do we use atom economy?

Answer 25

Considers not only the desired products but also the by-products, describing the efficiency of a reaction in terms of all atoms involved
Encourages companies to reduce waste

Question 26

Acid + metal ——>

Answer 26

Salt + hydrogen
(Classified as neutralisation and redox)

Question 27

Metal oxide + acid ——>

Answer 27

Salt + water
(Neutralisation)

Question 28

Metal hydroxide + acid —->

Answer 28

Salt + water
(Neutralisation)

Question 29

What is a displacement reaction

Answer 29

Chemical reactions in which a more aq metal (one which more readily loses electrons) displaces a less reactive metal from an aq solution of one of its salts
All displacement reactions are REDOX

Question 30

How does reactivity change as you go down group 7 (halogens)

Answer 30

Reactivity decreases down the group

Question 31

What are the uses of halogen displacement

Answer 31

Purification of water
Production of halogenated compounds

Question 32

What is a precipitation reaction

Answer 32

Substances in a solution are mixed and an insoluble product is formed.
The insoluble product is called a precipitate and can be seen as a solid forming in the reaction mixture

Question 33

What does qualitative mean

Answer 33

Measuring non-numerical data
Allows us to understand the characteristics of substances

Question 34

What does quantitive mean?

Answer 34

Measuring numerical data
Allows us to find kamounts’

Question 35

Describe a concentration test

Answer 35

Form precipitate, centrifuge, collect pellet, measure mass, calculate conc

Question 36

Describe a cation test

Answer 36

Flame tests
OR
add NaOH - precipitate forms, qualitative colour analysis :
Green= iron (II)
Brown= iron (III)
Blue = copper
If white, add excess NaOH , still white ? Aluminium, gone colourless? Calcium

Question 37

Acid + base ——>

Answer 37

Salt + water

Question 38

Acid + metal carbonate —->

Answer 38

Metal salt + carbon dioxide + water