Chapter 3 - Amount Of Substance

Question 1

Define the Avagardo Constant (Na)?

Answer 1

The number of atoms per mole of the carbon-12 isotope (6.02 x 10^23 mol^-1

Question 2

Define a mole?

Answer 2

Any substance containing as many particles as there are particles (atoms/molecules/ions/electrons) in 12 g of the carbon-12 isotopes

Question 3

Calculate the molar mass?

Answer 3

Molar mass (gmol^-1) = mass (g) / mole (mol)

Question 4

Define the relative formula mass?

Answer 4

Weighted mean mass of the formula unit compared to 1/12 of an atom of carbon-12

Question 5

Define what is meant by the empirical formula?

Answer 5

Simplest whole number ratio of atoms of each element present in compound

Question 6

Define what is meant by molecular formula?

Answer 6

The actual number of atoms of each element in a molecule

Question 7

How do you calculate the empirical formula?

Answer 7

Use EMMA R
•E = element
•M = mass (or %)
/
•M = molar mass (Ar)
•A = answer
•R = ratio (found by diving the answers by the smallest answer)

Question 8

What does •xH2O mean?

Answer 8

The water of crystallisation

Question 9

What does CoMMA R stand for?

Answer 9

• Co = compound
• M = mass
/
• M = molar mass
• A = answer
• R = Ratio

Question 10

What is stated in Avagadro’s Hypothesis?

Answer 10

Measuring one mole of a gas is the same as the volume

Question 11

Define what is meant by the molar volume?

Answer 11

The volume per mol of gas (dm^3mol^-1). At room temperature the molar volume is 24 dm^3mol^-1

Question 12

How do you convert amount in moles and gas volumes?

Answer 12

Volume = mol x 24 dm ^3 mol^-1

Question 13

What’s the ideal gas law equation?

Answer 13

Pressure (Pa) x volume (m^3) = mole x ideal gas constant (8.31 Jk^-1mol^-1) x temperature ( C° + 273)

pV = nRT

Question 14

How do you calculate the concentration in a solution?

Answer 14

Concentration (moldm^3) = mole/volume (dm^3)

Question 15

Define stoichiometry?

Answer 15

Molar relationship between the relative quantities of substances taking part in a reaction

Question 16

What could be limiting reagent?

Answer 16

• worked by moles
• not in excess
• calculations based on limiting reagent

Question 17

Calculate the percentage yield?

Answer 17

Percentage yield = ( actual yield/theoretical yield) x 100

Question 18

Why is it difficult to achieve 100% yield?

Answer 18

• reaction not gone to completion (equilibrium)
• different products formed
• loss of product during handling
• reversible reaction
• loss of product during purification

Question 19

Calculate the atom economy?

Answer 19

Atom economy = (molar mass desired/ molar mass of all products) x 100

Question 20

What’s the assumption for the molecules making up the ideal gas?

Answer 20

• random motion
• elastic collision
• negligible size
• no intermolecular forces

Question 21

What’s does hydrated mean?

Answer 21

A crystalline compound containing water molecules

Question 22

What does anhydrous mean?

Answer 22

Containing no water molecules