2.1.3 Amount of Substance

Question 1

What is a mole?

Answer 1

The unit for amount of substance (mol)

Question 2

What is the Avogadro constant?

Answer 2

The number of particles per mole (6.02 x10^23)

Question 3

What is the molar mass?

Answer 3

Mass per mole (g/mol)

Question 4

What is the molar gas volume?

Answer 4

The gas volume per mole (dm3/mol)

Question 5

What does empirical formula mean?

Answer 5

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

Question 6

What does molecular formula mean?

Answer 6

The number and type of atoms of each element in a molecule

Question 7

What does anhydrous mean?

Answer 7

Contains no water

Question 8

What does hydrated mean?

Answer 8

Contains water

Question 9

What does water of crystallisation mean?

Answer 9

When water is bonded to the lattice

Question 10

How do you calculate moles?

Answer 10

Moles = mass/molar mass
Gas volume = moles x 24dm3
Concentration = moles/volume

Question 11

What is the ideal gas equation?

Answer 11

pV = nRT

p - pressure (Pa)
V - volume (m3)
n - moles (mol)
R - gas constant
T - temperature (K)

Question 12

What are the standard conditions?

Answer 12

• 273K (standard) and 293K (room temp)
• 1atm = 101000Pa

Question 13

How do you calculate the percentage yield?

Answer 13

Percentage yield = actual mass/theoretical mass x 100

Question 14

What does the theoretical yield assume?

Answer 14

• No products are lost
• All reactants have reacted fully
• Therefore percentage yield is never 100%

Question 15

How do you calculate the atom economy of a reaction?

Answer 15

Atom economy = mass of useful products/total mass of products

Question 16

Why are high atom economies useful?

Answer 16

• Produce less waste
• Raw materials are used more efficiently
• Less by-products are formed so less time and money spent separating them
• Addition reactions always have 100% atom economy