Amount of substance

Question 1

What is meant by relative atomic mass? Ar

Answer 1

• average mass of one atom of an element
• divided by 1/12th mass of a C-12 atom

Question 2

What is meant by relative molecular mass?

Answer 2

• average mass of one molecule
• divided by 1/12th mass of a C-12 atom

Question 3

Moles/mass/Mr equation

Answer 3

Mass (g) = moles x Mr

Question 4

Moles/concentration/volume equation

Answer 4

moles = conc x volume (dm3)

Question 5

State the ideal gas equation

Answer 5

PV = nRT

P = Pascals
V = m3
T = Kelvin
R = 8.31 jk-1 mol-1

Question 6

Kpa into pascals?

Answer 6

multiply by 1000

Question 7

m3 to dm3?

Answer 7

multiply by 1000

Question 8

cm3 to m3?

Answer 8

divide by 1 x 10^6

Question 9

dm3 to m3?

Answer 9

divide by 1000

Question 10

dm3 to cm3?

Answer 10

multiply by 1000

Question 11

m3 to cm3?

Answer 11

multiply by 1 x 10^6

Question 12

m3 to dm3?

Answer 12

multiply by 1000

Question 13

What is meant by empirical formula?

Answer 13

• Simplest whole number ratio of atoms
• of each element in a compound

Question 14

What is meant by molecular formula?

Answer 14

• Actual number of atoms
• of each element in a compound

Question 15

% yield formula?

Answer 15

amount of specific product formed (actual) / theoretical maximum amount of product that could be formed (theoretical) x 100

Question 16

Describe how to make up a standard solution

Answer 16

Stage 1:
- weigh a sample bottle containing solid
- transfer to beaker and reweigh sample bottle
- record difference in mass

Stage 2:
- add distilled water
- stir with glass rod
- until all solid has dissolved

Stage 3:
- Transfer to volumetric flask
- with washings
- make up to 250cm with water
- shake/invert

Question 17

How to calculate percentage error?

Answer 17

% error = error of equipment/amount measured x 100

Question 18

Suggest a reason for removing the funnel after it has been used for filling the burette

Answer 18

• droplet from funnel could enter burette
• affects volume of

Question 19

During the titration, the inside of the conical flask is rinsed with distilled water.
Suggest why rinsing improves the accuracy of the titre

Answer 19

ensures all reactants are able to react

Question 20

During a titration, a chemist rinsed the inside of the conical flask with deionised water. The water used for rinsing remained in the conical flask.
Explain why the water used for rinsing has no effect on the accuracy of the titre.

Answer 20

does not change the number of moles of reactants in the conical flask

Question 21

A teacher noticed that a student had not cleared a large air bubble from below the burette tap in preparing the burette for use before starting the titration. This air bubble was ejected during the first titration of the volumetric flask mixture.
State the effect that this mistake would have on the value of the first titre.

Answer 21

Increase in volume of titre

Question 22

Space will fill during titration and titre will be too high. What is the cause of this?

Answer 22

not filling burette tap before starting titration

Question 23

Ensures all reagents are able to react. What is done in a titration to ensure this?

Answer 23

rinsing the walls of the conical flask with deionised water

Question 24

Less chance of losing liquid on swirling. What is done in a titration to ensure this?

Answer 24

using conical flask instead of a beaker

Question 25

A droplet could enter the burette and increase the titre. What is the cause of this?

Answer 25

leaving the funnel in the burette