2.1.3: 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 to calculate the mass of 1 mole of the element?

Answer 4

Mass of 1 mole = relative atomic mass in grams

Question 5

How to calculate moles when mass and molar mass are given?

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?

Answer 11

● They are in continuous motion.
● No intermoleculer 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

273 K.

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 are the four common state symbols?

Answer 21

1. Solid (s).
2. Liquid (l).
3. Gaseous (g).
4. Aqueous (aq).

Question 22

What does the percentage yield mean?

Answer 22

The efficiency of which reactants are converted into products.

Question 23

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

Answer 23

● 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 24

How is percentage yield calculated?

Answer 24

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

Question 25

What does atom economy tell us about?

Answer 25

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

Question 26

How is atom economy calculated?

Answer 26

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

Question 27

Does 100% yield mean 100% atom economy?

Answer 27

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

Question 28

Which type of reaction has 100% atom economy?

Answer 28

Addition reactions (two or more reactants are combined to form a product).