Amount of Substance

Question 1

what is a mole?

Answer 1

mass of a substance that has the same number of particles as there are in 12g of carbon 12

Question 2

what is Avogadro’s constant? what can it be used for?

Answer 2

• 6.022 x 10²³
• used to find the number of particles present in a sample of a substance with known mass

Question 3

give an equation to find the number of particles present in a sample of a substance with a known mass

Answer 3

number of particles = moles x Avogadro’s constant

Question 4

what is one mole of an atom equal to?

Answer 4

Ar of the atom in grams

Question 5

what is one mole of a molecule equal to?

Answer 5

Mr of the molecule in grams

Question 6

give an equation that links mass, mr and moles

Answer 6

mass = mr x moles

Question 7

give an equation that links pressure, volume, moles and temperature. state the units.

Answer 7

pv=nrt
- p = pressure in pa
- v = volume in m³
- n = moles
- R = gas constant
- t = temperature in K

Question 8

how do you convert dm³ to m³?

Answer 8

divide by 1000

Question 9

how do you convert cm³ to m³?

Answer 9

divide by 1,000,000

Question 10

what does Boyle’s law state?

Answer 10

• at a constant temp, the products of pressure and volume is a constant
• p x v = constant

Question 11

what does Charles’ law state?

Answer 11

• at a constant pressure, volume is proportional to temperature
• v/t = constant

Question 12

what does Gay-Lussac’s law state?

Answer 12

• at a constant volume, pressure is proportional to temperature
• p/t = constant

Question 13

explain how to calculate empirical formula?

Answer 13

1) find masses
2) look up Ar values
3) divide masses by Ar
4) find ratio

Question 14

explain how to work out the percentage composition (what percentage of a molecule is made up by an atom)

Answer 14

1) find Ar of atom and Mr of molecule
2) divide Ar by Mr (Ar/Mr)
3) multiply by 100

Question 15

explain how to calculate reacting masses

Answer 15

1) find masses
2) calculate Mr
3) calculate moles
4) find ratio from balanced equation
5) moles x mr

Question 16

explain how to calculate percentage atom economy

Answer 16

[(mr of desired product)/(total mr of reactants)] x 100

Question 17

explain how to find the molecular formula from the empirical formula

Answer 17

(Mr of molecule)/(empirical Mr) = multiplier

Question 18

explain how to calculate percentage yield

Answer 18

(actual yield)/(theoretical yield) x 100

Question 19

why is it good to have as high of an atom economy as possible?

Answer 19

• little to no waste product
• more economically viable
• uses less natural resources and therefore often uses less energy