2.1.3 Amount of Substances

Question 1

Definition of amount of substance

Answer 1

its the quantity that has moles as its unit. Chemist use ‘amount of substance’ as a way of counting atoms.

Question 2

Define mole (symbol mol)

Answer 2

its the unit for amount of substances

Question 3

Definition of Avogadro constant, na

Answer 3

the number of particles per mole

Question 4

What is the Avagardo constant

Answer 4

6.02 X 10^23 mol^-1

Question 5

Definition of molar mass

Answer 5

Its the mass per mole of a substance, units g mol^–1

Question 6

Definition of molar gas volume

Answer 6

Its the volume per mole of a gas, units dm^3 mol^–1

Question 7

Definition of Empirical Formula

Answer 7

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

Question 8

Definition of Molecular Formula

Answer 8

Its the number and type of atoms of each element in a molecule

Question 9

What is one mole?

Answer 9

Its the amount of substances that contains 6.02 X 10^23 mol^-1 particles.

Question 10

what is the triangle for moles from a mass?

Answer 10

Mass / moles X Mr

Question 11

How do you find out the empirical formula?

Answer 11

1. divide the amount of each element present by its molar mass
2. divide the answer for each element by the smallest number

Question 12

How do you find out the molecular mass?

Answer 12

1. Add the relative atomic mass
2. Mr / relative atomic mass
3. answer to 2 x the compound

Question 13

what is the triangle for moles from a gas volume in dm^3?

Answer 13

v / moles X 24.0

Question 14

what is the triangle for moles from solution in dm^3?

Answer 14

moles / conc X volume

Question 15

what is the triangle for moles from a gas volume in cm^3?

Answer 15

v / moles X 24’000

Question 16

what is the triangle for moles from solution in cm^3?

Answer 16

moles / conc X (volume / 1000)

Question 17

What is the ideal Gas equation?

Answer 17

pV = nRT

Question 18

How do you find out the percentage yield?

Answer 18

1. Calculate the amount, in mol, of product used
2. Calculate the amount in mol, of expected product - by checking if the equation is a 1:1 ratio
3. Find the actual amount, in mol, of product made
4. Actual amount, in moles
   ———————————- X 100
   Expected amount , in moles

Question 19

How do you find out the atom economy?

Answer 19

molecular mass of the desired product
——————————————————— X 100
Sum of molecular masses of all product

Question 20

Why is percentage yield more likely to be less than 100%?

Answer 20

> Reactant may not be pure
Seperation and Purification may result in loss of the product
Some reactant may be left behind in the apparatus used in the experiment
Side reaction may occur, leading to by-products

Question 21

How does high atom economy benefit the society?

Answer 21

> Hight atom economy reduce the amount of waste produced

> Reactions with high atom economy make processes much more sustainable