Module 2 - Amounts 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

mol

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? (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

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)

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)