1. Stoichiometric Relationships

Question 1

What is a mole?

Answer 1

A unit that measures the amount of substance.

Question 2

How many elementary entities are in one mole?

Answer 2

6.02 x 10^23

Question 3

What is an elementary entity?

Answer 3

Any particle. Eg: an atom, molecule or ion.

Question 4

N= ?

Answer 4

n x NA

Question 5

What is the molar mass?

Answer 5

The mass of one mole of an element/ compound.

Question 6

n= ?

Answer 6

m/ M

Question 7

N/ NA = ?

Answer 7

m/ M

Question 8

Define ‘molecular formula’.

Answer 8

The actual number of atoms in a compound.

Question 9

Define ‘empirical formula’.

Answer 9

The simplest whole number ratio of atoms in a compound.

Question 10

What are the units for molar mass?

Answer 10

gmol-1

Question 11

How do you find the limiting reactant?

Answer 11

Divide the given moles by the stochiometric coefficient.

Question 12

Define ‘theoretical yield’.

Answer 12

The mass of product formed if reactants react completely, according to molar ratios.

Question 13

Define ‘actual yield’.

Answer 13

The mass of product obtained in a reaction.

Question 14

Define ‘percentage yield.’

Answer 14

A measure of the reaction efficiency.

Question 15

What is the formula for percentage yield?

Answer 15

(Actual yield/ theoretical yield) x100

Question 16

Give 5 reasons why a reaction may not be 100% efficient.

Answer 16

• Transfer losses (left in glassware)
• Side reactions.
• Reaction reaches equilibrium.
• Reactants may be impure.
• Reaction is slow.

Question 17

Define ‘atom economy’.

Answer 17

A measure of efficiency that assesses how many reactant atoms are transformed to the desired products.

Question 18

What is the formula for atom economy?

Answer 18

Atom economy= (Mr of desired product/ sum of Mr of all products) x100

Question 19

Give 2 ways that atom economy can be improved.

Answer 19

• Undesired products can be recycled within a chemical plant.
• Undesired products can be bought by another company for another process.

Question 20

For gases, moles= ?

Answer 20

volume / molar volume

Question 21

State Avogadro’s Law.

Answer 21

The volume of gas is directionally proportional to the number of moles.

Question 22

At stp, how much volume does one mole of gas occupy?

Answer 22

22.7 dm-3

Question 23

What are the values of standard temperature and pressure?

Answer 23

273K and 100KPa

Question 24

What is a homogeneous reaction?

Answer 24

A reaction where all of the species are in the same phase.

Question 25

What is a heterogeneous reaction?

Answer 25

A reaction where the species are in different phases.

Question 26

Density= ?

Answer 26

Mass/ volume

Question 27

State the 5 assumptions of an ideal gas.

Answer 27

• Gas molecules are in a constant, random motion.
• Molecular collisions are perfectly elastic.
• The volume occupied by gas molecules is negligible.
• There are no intermolecular forces.
• Kinetic energy is directionally proportional to temperature in Kelvin.

Question 28

At which temperatures do real gases act least like ideal gases?

Answer 28

At low temperatures, kinetic energy falls. Upon collision, attractive forces form and collisions are not elastic.

Question 29

At which pressures do real gases act least like ideal gases?

Answer 29

At high pressures, there are more molecules in the space so the volume of particles becomes more significant.

Question 30

In which conditions does a gas behave like an ideal gas?

Answer 30

High temperatures and low pressures.

Question 31

(P1V1) / T1= ?

Answer 31

(P2V2) / T2

Question 32

PV= ?

Answer 32

nRT

Question 33

What is the formula for percentage uncertainty?

Answer 33

(Total uncertainty/ measured uncertainty) x100

Question 34

What are the units for Avogadro’s constant?

Answer 34

mol-1

Question 35

concentration= ?

Answer 35

moles x volume

Question 36

How many dm3 is 1cm3

Answer 36

0.001

Question 37

What is the formula for ppm?

Answer 37

Ppm= (mass/ total mass of solution) x 1,000,000

Question 38

C1V1= ?

Answer 38

C2V2