C4 Caluculations

Question 1

What is a mole?

Answer 1

mass of a substance that contains 6.02×10 to the power of 23 particles

Question 2

Give the value for Avogadro’s constant.

Answer 2

6.02x10 to the power 23

Question 3

Which formula is used to calculate the number of moles from mass and Mr?

Answer 3

moles = mass/
Mr

Question 4

Which formula is used to calculate the mass of a substance from number of moles and Mr?

Answer 4

mass = moles × Mr

Question 5

What is a limiting reactant?

Answer 5

the reactant that is completely used up in a chemical reaction

Question 6

What is a unit for concentration?

Answer 6

g/dm3 or mol/dm3

Question 7

which formula is used to calculate concentration from mass and volume?

Answer 7

concentration (g/dm3) = mass (g) / volume (dm3)

Question 8

Which formula is used to calculate volume from concentration and mass?

Answer 8

volume (dm3) = mass (g) /concentration (g/dm3)

Question 9

Which formula is used to calculate mass from concentration in g/dm3 and volume?

Answer 9

mass (g) = concentration (g/dm3) x volume (dm3)

Question 10

How can you convert a volume reading in cm3 to dm3?

Answer 10

divide by 1000

Question 11

If the amount of solute in a solution is increased, what happens to its concentration?

Answer 11

increases

Question 12

If the volume of water in a solution is increased, what happens to its concentration?

Answer 12

decreases

Question 13

What is the yield of a reaction?

Answer 13

mass of product obtained from the reaction

Question 14

What is the theoretical yield of a reaction?

Answer 14

maximum mass of the product that could have been produced.

Question 15

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

Answer 15

• reaction may be reversible
• some of the product can be lost on separation
• unexpected side reactions between reactants

Question 16

How is percentage yield calculated?

Answer 16

Actual yield/theoretical yield x 100

Question 17

What is atom economy?

Answer 17

measure of how many atoms of the reactants end up as useful products

Question 18

Why is a high atom economy desirable?

Answer 18

results in less waste/is more sustainable

Question 19

How is percentage atom economy calculated?

Answer 19

Mr of useful product/Mr of all product x 100

Question 20

How can concentration be calculated?

Answer 20

Moles of solute/volume(dm3)

Question 21

What is a titration?

Answer 21

method used to calculate the concentration of an unknown solution

Question 22

What is the end-point?

Answer 22

the point at which the reaction is complete (when the indicator changes colour) and no substance is in excess

Question 23

How should solution be added from the burette close to the end point?

Answer 23

drop by drop, swirling in between

Question 24

Why is a white tile used in titration?

Answer 24

to see the colour change better

Question 25

What is a titre?

Answer 25

volume of solution added from the burette

Question 26

What volume does one mole of any gas occupy at room temperature and pressure?

Answer 26

24 dm3 or 24000 cm3

Question 27

What is the percentage yield?

Answer 27

actual yield as a portion of its theoretical yield