M2 - Amount of Substance

Question 1

How is the molecular formula found?

Answer 1

Find empirical formula.
Divide molar mass of a molecule by molar mass of empirical formula.
Multiply empirical formula by the result.

Question 2

What is the equation for the number of moles of a substance?

Answer 2

n=m/Mr
n - number of moles (mol)
m - mass (g)
Mr - molar mass (g/mol)

Question 3

Define empirical formula (1)

Answer 3

Simplest whole number ratio of atoms

Question 4

What is the percentage yield?

Answer 4

The actual yield divided by the theoretical yield expressed as a percentage.

(actual yield / theoretical yield ) X100

Question 5

What is the concentration of a solute?

Answer 5

The amount of solute (in moles) dissolved in each 1dm^3 of solution

Question 6

What is the value of gas molar volume at room temperature and pressure?

Answer 6

1 mole of any gas takes up 24 dm^3/mol at rtp

Question 7

What is gas molar volume?

Answer 7

The volume per mole of a gas.

Measured in dm^3/mol

Question 8

What are the benefits of a high atom economy?

Answer 8

Produce a larger proportion of desired products and few waste products.
Important for sustainability, the best use of natural resources.

Question 9

How is the empirical formula found?

Answer 9

E   Element
M  Mass or %
---  ----------------
M  Molar mass
A   Answer (moles)
     ------------------------
     Smallest answer
R   Ratio

Question 10

What is atom economy?

Answer 10

The molar mass of desired product divided by the sum of the molar masses of all products expressed as a percentage.

(mr of desired products/ mr of total products) X100

Question 11

What is a titration?

Answer 11

A technique used to accurately measure the volume of one solution that reacts exactly with another solution.

Question 12

Answer 12

D

Question 13

When can a mean titre be worked out?

Answer 13

When two or more concordant results are obtained.

Question 14

What is relative formula mass?

Answer 14

The weighted mean mass of the formula unit of a compound compared with 1/12th of an atom of carbon-12

Question 15

What is stoichiometry?

Answer 15

The balancing numbers giving the ratio of the amount, in moles, of each substance in a balanced equation.

Question 16

Answer 16

A

Question 17

What is the empirical formula?

Answer 17

The simplest whole-number ratio of atoms of each element in a compound.

Question 18

What is the equation to calculate moles of a gas at RTP?

Answer 18

n = v / 24

molar gas volume = 24 (dm^3/mol)
n - number of moles (mol)
V - volume (dm^3)

Question 19

Answer 19

C

Question 20

What are titrations used for?

Answer 20

titrations are used for Finding the concentration of a solution.
Identification of unknown chemicals.
Finding the purity of a substance.

Question 21

What are the standard conditions for temperature and pressure?

Answer 21

T = 298K or 25C
P = 1atm or 100kPa

101kPa or 1 atm of pressure

Question 22

What is the limiting reagent?

Answer 22

The reactant that is not in excess.

Question 23

What is the molecular formula?

Answer 23

The number of atoms of each element in a molecule.

Question 24

Answer 24

D

Question 25

What is the equation for finding a solution’s concentration?

Answer 25

c=n/v
c - concentration (mol/dm^3)
n - number of moles (mol)
v - volume (dm^3)

Question 26

In hydrated salts, what is the name given to water molecules?

Answer 26

Waters of crystallisation

Question 27

Why is the theoretical yield so hard to achieve?

Answer 27

The reaction is incomplete.
Competing side reactions giving different products.
Loss of product in handling and purification.
Reversible reaction.

Question 28

Answer 28

B

Question 29

What is a mole?

Answer 29

The amount of any substance containing as many particles as there are particles in 12g of the carbon-12 isotope.

Question 30

What is relative molecular mass?

Answer 30

The mass of a molecule compared with the mass of an atom of carbon-12.

Question 31

Explain what is meant by molecular formula (1)

Answer 31

Number and type of atoms making up a molecule

Question 32

Answer 32

C

Question 33

What are concordant results?

Answer 33

Within 0.10 cm^3 of each other.

Question 34

What are the assumptions made about an ideal gas?

Answer 34

Random motion
Elastic collisions
Negligible size
No intermolecular forces

Question 35

What is Avogadro’s Constant?

Answer 35

The number of atoms in one mole of the carbon-12 isotope. found in data sheet 6.02X10^23

Question 36

Outline the steps to prepare a 250 cm3 standard solution

Answer 36

step 1: find mass of chemical compound you want
step2:
weigh the solid and then
dissolve it, with stirring, in distilled water
pour solution into a 250cm3 volumetric flask
rinse beaker with distilled water into the flask
add distilled water to flask - bottom of meniscus on graduation line
place stopper on flask and invert

Question 37

Answer 37

B

Question 38

What is meant by the term mole? (1)

Answer 38

Amount of substance that has the same number of particles as there are atoms in 12g of carbon 12

Question 39

What is the ideal gas equation?
State the standard units for each.

Answer 39

pV=nRT
p - pressure (Pa)
V - volume (m^3)
n - number of moles (mol)
R - gas constant, 8.314 (J/mol/K)
T - temperature (K)

Question 40

What term is given to the .n H2O part of a formula? (1)

Answer 40

Waters of crystallisation

Question 41

What are the balanced equations used to find?

Answer 41

The quantities of reactants required to prepare a required quantity of a product.
The quantities of products that should be formed from certain quantities of reactants.

Question 42

Answer 42

B

Question 43

Answer 43

C