1.2 Amount of Substance

Question 1

What is the symbol for amount of substance?

Answer 1

n

Question 2

What is the unit used to measure amount of substance?

Answer 2

mole

Question 3

What does the Avogadro constant represent?

Answer 3

The number of atoms per mole of the carbon-12 isotope

Question 4

How is the mass of 1 mole of the element calculated?

Answer 4

Mass of 1 mole = relative atomic mass in grams

Question 5

How are the moles when mass and molar mass are given calculated?

Answer 5

Moles (mol) = mass (g) / molar mass (g mol -1)

Question 6

State Avogadro’s law

Answer 6

Under the same temperature and pressure, one mole of any gas would occupy the same volume.

Question 7

How much volume does a gas
occupy, at room temperature
and pressure?

Answer 7

24 dm3

or 24000 cm3

Question 8

Define molar gas volume

Answer 8

The volume per mole of gas molecules

Question 9

Why do different gas particles occupy the same volume?

Answer 9

The gas particles are very spread out, hence individual differences has no effect.

Question 10

How to calculate moles when gas volume is given?

Answer 10

Moles (mol) = volume (dm3) / 24
Or
Moles (mol) = volume (cm3) / 24000

Question 11

What are the ideal ways in which gases behave?

5

Answer 11

● They are in continuous motion
● No intermolecular forces experienced
● Exert pressure when they collide with each other or container
● No kinetic energy is lost in the collisions
● When temperature increases, kinetic energy of gases also increase

Question 12

Write down the ideal gas equation (in words and symbols, including the units)

Answer 12

pV = nRT

Pressure (Pa) x volume (m3) = number of moles (mol) x gas constant (8.314 J mol-1) x temperature (K)

Question 13

1 atmospheric pressure is equal to how many pascal?

Answer 13

1 atm = 101325 Pa

Question 14

0℃ is equal to how many kelvin?

Answer 14

273K

Question 15

What does concentration of a solution mean?

Answer 15

It is the amount of solute dissolved in 1 dm3 of solvent

Question 16

How do you calculate moles when concentration and volume are given?

Answer 16

Moles (mol) = concentration (mol dm-3) x volume (dm3)

Question 17

What is a standard solution?

Answer 17

A solution of known concentration

Question 18

Write down the steps to prepare a standard solution

Answer 18

1. Weigh the solute using the weigh by difference method
2. In a beaker dissolve the solute using the solvent
3. Pour the solution into a volumetric flask
4. Rinse the beaker using the solution and add it to the flask
5. Add solvent to the flask carefully until it reaches the graduation
   line
6. Mix the solution thoroughly to ensure complete mixing

Question 19

What does the terms concentrated and dilute mean?

Answer 19

Concentrated - large amount of solute per dm3 of solvent

Dilute - small amount of solute per dm3 of solvent

Question 20

What is a species in a chemical reaction?

Answer 20

Any particle that takes part in a reaction

Question 21

What does percentage yield mean?

Answer 21

The efficiency of which reactants are converted into products

Question 22

What are the reasons for not obtaining 100% yield? (5)

Answer 22

● Reaction may be at equilibrium
● The reactants may be impure
● Side reactions could happen
● Reactants or products may be left behind while transferring
● Loss of products during separation and purification

Question 23

How is percentage yield calculated?

Answer 23

Percentage yield = (actual amount of product (mol) / theoretical amount of product (mol)) x 100

Question 24

What does atom economy tell us about?

Answer 24

The proportion of desired products compared with all the products formed in the reaction

Question 25

How is atom economy calculated?

Answer 25

Atom economy = (molecular mass of desired product / sum of the molecular masses of all products) x 100

Question 26

Does 100% yield mean 100% atom economy?

Answer 26

No, even if all the reactants are converted into products, not all products of the reaction will be the required products

Question 27

Which type of reaction has 100% atom economy?

Answer 27

Addition reactions