Quantitative Analysis - Topic 5

Question 1

How do you calculate percentage yield?

Answer 1

% yield = (actual yield (given in Q) / theoretic yield) x 100

Question 2

What does the % yield compare?

Answer 2

compares the amount of product produced versus the maximum amount of product that could be expected when all the reactants reacted

Question 3

What is the actual yield usually like in comparison to the theoretic yield?

Answer 3

the actual yield usually less than the theoretical yield

Question 4

Why is the actual yield usually less than the theoretical yield?

Answer 4

1. Incomplete reaction - some reactant remained unreacted, reaction not left long enough
2. Practical loss of product during the experiment
3. Competing, unwanted, side reactions which produce different products
4. Impurities in reaction
5. (Reversible and in equilibrium reaction)

Question 5

Calculate the atom economy of a reaction forming a desired product:

Answer 5

% atom economy = mass desired product/total mass of reactants x 100

Question 6

How does atom economy relate to sustainable development?

Answer 6

• due to damage being caused to the planet by human activity, environmentalists are calling for a change of direction towards more sustainable development
• as the amount of available resources decrease it is vital that resources are used as efficiently as possible
• to reduce global impact of all industrial processes, scientists aim to design reactions which have the highest possible atom economy, thereby reducing the raw materials used and the amount of energy needed to produce any product
• more products —> worse atom economy
• 1 product = 100% atom economy

Question 7

Sustainability:

Answer 7

meeting present needs for development without compromising the ability of future generations to meet their own needs

Question 8

What does sustainable development adopt?

Answer 8

• sustainable development adopts strategies that allow for the exploitation of natural resources
• whilst minimising the damage caused by the extraction of resources, or by the production of finished products

Question 9

What will equal volumes of all gases contain?

Answer 9

equal volumes of all gases will contain the same number of molecules as long as the temperature and pressure are the same

Question 10

Avogadro’s number:

Answer 10

6.02 x 10²³

Question 11

How do you find number of molecules of a gas in a volume?

Answer 11

1. Find number of moles
2. Multiply number of moles by Avogadro’s number

Question 12

How do you calculate concentration (g/dm3)?

Answer 12

• concentration (g/dm3) = mass (g) / volume (dm3)
• concentration (g/dm3) = concentration (mol/dm3) x Mr

Question 13

How do you calculate concentration (mol/dm3)?

Answer 13

• concentration (mol/dm3) = number of moles (mol) / volume (dm3)

Question 14

What is 1dm3 in cm3?

Answer 14

1dm3 = 1000cm3

Question 15

What volume does one mole of gas occupy?

Answer 15

24,000cm3 OR 24dm3

Question 16

How do you find the volume that a gas takes up?

Answer 16

Volume gas takes up = no. Of moles x 24dm3 (24,000cm3)

Question 17

How do you find the number of gas molecules in a certain gas?

Answer 17

gas molecules = moles x Avogadro’s number

Question 18

What can you do with the unwanted products in a reaction to maximise profits?

Answer 18

sell the other products from the reaction

Question 19

How do you calculate the number of moles in a certain volume of gas?

Answer 19

moles = vol / 24dm3

Question 20

Molar volume:

Answer 20

• volume of gas occupied by one mole of molecules at room temperature and pressure
• 24,000 cm³ (or 24dm³)

Question 21

Actual yield:

Answer 21

The amount/mass of product produced in the reaction

Question 22

Theoretic yield:

Answer 22

The maximum amount/mass of product produced if all reactants reacted completely with no losses OR the calculated mass of product formed if all reactants used to form products with no losses