1.2 Amount of Substance

Question 1

How do you know a chemical reaction has taken place?

Answer 1

Colour change
Effervescence 
Temperature 
Light
Precipitate formed (cloudy)
Change in mass 
Sound
pH change

Question 2

What do the small numbers represent within an equation?

Answer 2

They say how many atoms of that element are within the molecule

Question 3

What is the Mr?

Answer 3

Relative Molecular Mass

The average mass of a molecule compared to 1/12 of the mass of one atom of carbon-12

Question 4

What is the Ar?

Answer 4

Relative Atomic Mass

Average mass of an atom compared to 1/12 of one atom of carbon-12

Question 5

What is used to compared relative masses?

Answer 5

The carbon 12 scale

Question 6

What unit is used for Mr?

Answer 6

gmol ^-1

Question 7

How do you calculate the Mr?

Answer 7

Add up all the atomic mass numbers in the molecule

Question 8

How to work out percentage of an element within a compound?

Answer 8

Ar of element
Divided by
Mr of compound
Multiplied by 100

Question 9

How do you work out the transition element charges?

Answer 9

They should be given to you as a roman numeral 
I - 1+
II - 2+
III - 3+ 
IV - 4+ 
Etc....

Question 10

Definition of an element?

Answer 10

A substance in which all the atoms contain the same number of protons

Question 11

Definition of an atom?

Answer 11

The smallest part of an element that can take part in a chemical reaction

Question 12

Definition of an ion?

Answer 12

An atom that has either lost electrons to form a positive ion or gained electrons to form a negative ion
Atoms do this to make a full outer shell of electrons

Question 13

Definition of a molecule?

Answer 13

The smallest particle of a compound (a combination of two or more elements)
Also a name for elements that cannot exist as atoms in a free state

Question 14

Which elements cannot exist as atoms in a free state?

Answer 14

Diatomic molecules
Hydrogen - H2
Nitrogen - N2
Chlorine - Cl2
Iodine - I2
Oxygen - O2
Fluorine - F2
Bromine - Br2

Question 15

What is the charge of ammonium?

Answer 15

NH4 ^ 1+

Question 16

What is the charge of chloride, bromide and iodide?

Answer 16

Cl ^ 1-
Br ^ 1-
I ^ 1-

Question 17

What is the charge of hydroxide?

Answer 17

OH ^ 1-

Question 18

What is the charge of nitrate and nitrite?

Answer 18

NO3 ^ 1-

NO2 ^ 1-

Question 19

What is the charge of hydrogen carbonate and hydrogen sulphate?

Answer 19

HCO3 ^ 1-

HSO4 ^ 1-

Question 20

What is the charges of sulphate, sulphite and sulphide?

Answer 20

SO4 ^ 2-
SO3 ^ 2-
S2 ^ 1-

Question 21

What is the charges of oxide, carbonate and phosphate?

Answer 21

O2 ^ 1-
CO3 ^ 2-
PO4 ^ 3-

Question 22

What does aqueous mean?

Answer 22

Dissolved in water

Question 23

What are the symbols for:
hydrochloric acid
Sulphuric acid
Nitric acid
Ethanoic acid

Answer 23

HCl
H2SO4
HNO3
CH3COOH

Question 24

What are the symbols for ammonia
Carbon monoxide
Sulphur dioxide
Methane

Answer 24

NH3
CO
SO2
CH4

Question 26

What is the law of conservation of mass?

Answer 26

Total mass of reactants = total mass of products

Question 27

What are the rules for balancing combustion reactions?

Answer 27

Balance the carbons with CO2 Balance the hydrogen with H2O Balance the oxygen with O2

Question 28

What can you use with balancing equations?

Answer 28

Halves for the big numbers

Question 29

What can you not do when balancing equations?

Answer 29

Use or adjust small numbers to balance

Question 30

What must you remember about significant figures?

Answer 30

Your answer should always be the same number of significant figures as the smallest significant figure in the question

Question 31

How do you do empirical formula?

Answer 31

Divide the % or mass of the element by it’s Ar Divide all the answers by the smallest answer produced The whole numbers produced shows the EF You may have to multiply the ratios to create whole numbers

Question 32

How do you work out the molecular formula?

Answer 32

Mr/EF mass = x x multiplied by EF

Question 33

What does a mole contain?

Answer 33

1 mole of any substance contains 6.02 x10 ^23 particles Or Avagadros number

Question 34

What is Avagadros number? What contains it?

Answer 34

6.02 x10 ^23 The Ar and Mr of a substance in grams contains Avagadros number of particles

Question 35

What equation works out moles?

Answer 35

Mass ——— Moles X RFM

Question 36

What units are used for mass, moles and RFM?

Answer 36

Mass - g Moles - mol RFM (Ar/Mr) - gmol ^-1

Question 37

What do the large numbers represent in balancing equations?

Answer 37

The number of moles

Question 38

How do you calculate reacting masses?

Answer 38

Check equation is balanced Use the mass in the question divided by it’s RFM to work out the moles Use the moles to multiply by the RFM of the substance you are working out If it asks for the molecules multiply Be Avagadros If it asks for atoms multiply by Avagadros then the number of the atoms

Question 39

What is atom economy?

Answer 39

RFM of Useful products ———————————— x100 RFM of ALL the reactants

Question 40

How can any atom economy be improved?

Answer 40

Find a use for the waste/non useful product Sell the waste product

Question 41

What should you remember in atom economy?

Answer 41

Take note of the big numbers when working out the RFM’s

Question 42

What is significant about impure substances?

Answer 42

You cannot work out the moles or masses of impure substances

Question 43

What is the second equation that works out moles?

Answer 43

Moles ————————— Concentration X Volume

Question 44

What is the unit of volume (in mol, conc, vol)? Converting?

Answer 44

Dm^3 Cm^3 / 1000 = dm^3

Question 45

What are the units for concentration?

Answer 45

mol dm^3 Or M

Question 46

What is the equation for gases at room temperature and pressure?

Answer 46

Volumes ——————— Moles X 24dm^3

Question 47

What is the equation for gases at standard temperature and pressure?

Answer 47

Volumes ——————— Moles X 22.4 dm^3

Question 48

What are the conditions for room temperature and pressure?

Answer 48

298K | 100kPa

Question 49

What are the conditions for standard temperature and pressure?

Answer 49

273K | 101.3 kPa

Question 50

What is the ideal gas equation?

Answer 50

V P = n R T ``` V - volume P - pressure n - moles R - ideal gas constant T - temperature ```

Question 51

Units for pressure? Conversions?

Answer 51

Pascals - Pa kPa X 1000 = Pa

Question 52

What is the ideal gas constant?

Answer 52

8.31 J k^-1 mol^-1

Question 53

Units for temperature? Conversions?

Answer 53

Kelvin (K) Celsius + 273 = Kelvin

Question 54

Units for volume (in pv=nrt)? Conversions?

Answer 54

m^3 cm^3 / 1000000 = m^3 dm^3 / 1000 = m^3

Question 55

What is the equation for instrument error percentage?

Answer 55

Number of measurements X Instrument error —————————————— Measurement value All multiplied by 100

Question 56

How can you decrease instrument error?

Answer 56

Increase the measurement value

Question 57

What do you do if you’re bot told which reactant is in excess?

Answer 57

Find the limiting reagent by working out the moles of both

Question 58

How to work out the limiting reagents?

Answer 58

Work out the moles of both Use the moles of one of the reactants to predict the moles of the other reactant Compare the predicted moles to the actual moles If the actual moles is greater than the predicted then that reactant is in excess If the actual moles is smaller than the predicted moles then that reactant is the limiting factor