2.1.3 - Amount Of Substances

Question 1

What is the definition of a mole?

Answer 1

The amount of any substance that contains as many particles as there are carbon atoms in exactly 12g of the carbon-12 isotope

Question 2

How do you work out the number of particles in an molecule?

Answer 2

Avagadros constant x moles

Question 3

How do you work out the amount of moles in a substance?

Answer 3

Mass / Mr

Question 4

What is an empirical formula?

Answer 4

The simplest whole number ratio of atoms of each element present in a compound

Question 5

What is the molecular formula?

Answer 5

The actual number of each type of atom that makes up each molecule

Question 6

How do you work out the empirical formula?

Answer 6

1. Work out the molar ratio (mass/mr)
2. Divide each ratio by the smallest ratio
3. The number is = to the number of each element

Question 7

How do you work out the molecular formula?

Answer 7

1. Work out the mass of the empirical formula (CH2 = 14)
2. Mr / mass
3. The number of each element x answer

Question 8

What does hydrated mean?

Answer 8

Something containing water

Question 9

What does anhydrous mean?

Answer 9

Something that does not contain water

Question 10

What is water of crystallisation?

Answer 10

The water molecules that are bonded into a crystalline structure of a compound

Question 11

How do you work out the number of water molecules in a hydrated salt?

Answer 11

1. Calculate the mass of H2O
2. Calculate the moles of H2O and the other substance
3. Divide by the smallest mole to find the ratio

Question 12

How do you work out the moles in a solution?

Answer 12

Concentration x volume

Question 13

How do you work out the concentration of a dilute solution?

Answer 13

Concentration 1 x Volume 1 = Concentration 2 x Volume 2 (both volumes added together)

Question 14

How do you convert mol dm-3 —> g dm3?

Answer 14

Moles x Mr

Question 15

How do you work out the amount of moles in a gas?

Answer 15

Volume / 24 (dm3) or Volume / 24000 (cm3)

Question 16

What is the ideal gas equation?

Answer 16

Pressure x Volume = Moles X 8.314 X Tenperature or pV=nRT

Question 17

How do you convert kPa to Pa (pressure)?

Answer 17

X10^3

Question 18

How do you convert degrees to kelvin (temp)?

Answer 18

+273

Question 19

How do you convert dm3 to m3?

Answer 19

X10^-3

Question 20

How do you convert cm3 to m3 (volume)?

Answer 20

X10^-6

Question 21

What is room temp and pressure?

Answer 21

25 degrees and 101kPa

Question 22

What does stoichiometry mean?

Answer 22

A balanced equation

Question 23

How do you work out the mass of different elements in a compound?

Answer 23

1. Calculate the moles
2. Find the molar ratio
3. Moles x Mr = mass