Module 2 Teacher 2

Question 1

Equation for moles of a solid:

Answer 1

Mass = moles x RFM

Question 2

Equation for moles of a solution:

Answer 2

Moles = concentration x volume

Question 3

Equation for moles of a gas:

Answer 3

Moles = volume / 24

Question 4

Definition of relative isotopic mass:

Answer 4

Relative isotopic mass is the mass of an atom of an isotope compared with one twelfth of the mass of an atom of carbon-12.

Question 5

Definition of relative atomic mass:

Answer 5

Relative atomic mass is the weighted mean mass of an atom of an element compared with one-twelfth of the mass of an atom of carbon-12.

Question 6

Formula to find the Ar of an element:

Answer 6

(% of A in isotope x relative atomic mass of A) / 100 + (% of B in isotope x relative atomic mass of B) / 100

Question 7

What is the Avogadro’s Constant?

Answer 7

The number of particles per mole of a substance.

Question 8

What is the molar mass?

Answer 8

The mass per mole of a substance in gmol^-1, (the Mr)

Question 9

Equation for the percentage composition of an element in a compound?

Answer 9

% composition = (mass of element / total mass of compound) x 10
= ((number of atoms x relative atomic mass) / relative molecular mass) x 100

Question 10

What equipment can you use to find the mass compositions of a substance?

Answer 10

Mass spectrometer

Question 11

What is the ideal gas equation?

Answer 11

pV=nRT

p = pressure (Pa) (101kPa=1atm)
V = volume (m^3)
n = number of moles (mol)
R = molar gas constant (8.314 JK^-1)
T = temperature (K) (273°K = 0°C)

Question 12

What is the calculation for atom economy?

Answer 12

Molecular mass of desired products / sum of molecular mass of all products (or reactants) x 100

Question 13

How can atom economy benefit society?

Answer 13

We become more aware of the natural environment, waste products can be reduced, more sustainable, less expensive.

Question 14

Calculation for percentage yield?

Answer 14

Actual amount of product collected in mol / theoretical amount in mol x 100

Question 15

Why might a yield not be 100% (5)

Answer 15

-the reaction may be equilibrium and may not go to equilibrium.
-side reactions may occur leading to byproducts.
-the reactants may not be pure.
-some of the reactants or products may be left on the apparatus used in the experiment.
-separation and purification may result in the loss of some of the products.

Question 16

What are the formulae of different common acids and bases?

Answer 16

Acids: HCl, H2SO4, HNO3 and CH3COOH (acetic acid)
Alkalis: NaOH, KOH and NH3

Question 17

What do acids and alkalise release in aqueous solution?

Answer 17

Acids release H+ ions in aqueous solution and alkalis release OH– ions in aqueous solution.

Question 18

What’s the difference between a weak and strong acid?

Answer 18

Strong acids fully disassociate in water. All their hydrogen atoms are ionised.
(HCl + H2O -> H+ + Cl-)
(CH3COOH <-> CH3COO- + H+)

Question 19

What is neutralisation?

Answer 19

H+ and OH– to form H2O

Question 20

What is oxidation?

Answer 20

The loss of electrons shown by an increase in oxidation number.

Question 21

What is reduction?

Answer 21

The gain of electrons shown by the oxidation number decreasing.

Question 22

What are the rules for assigning oxidation numbers?

Answer 22

Combined fluorine: -1
Group 1 metals: +1
Group 2 metals: +2
Combined hydrogen: +1
Hydrogen in metal hydrides: -1
Combined oxygen: -2
Aluminium: +3
Uncombined elements: 0

Question 23

What is an isotope?

Answer 23

Atoms of the same element with different numbers of neutrons and different masses.

Question 24

How do you find the relative isotopic mass from mass spectrometry?

Answer 24

(mass A x %A + mass B x %B) / mass A + mass B

Question 25

How do you make a standard solution?

Answer 25

1. Weigh out a precise amount of solid using a balance.
2. Add a small volume of distilled water to it in a beaker and stir with a glass rod so it dissolves.
3. Transfer to a volumetric flask using a funnel.
4. Rinse the beaker and glass rod with distilled water and add the rinsings to the flask.
5. Make up to the scratch mark with more distilled water.
6. Add a stopper and mix the contents.

Question 26

How do you perform a titration?

Answer 26

1. Do a rough one, then add until 2 cm^3 off of it.
2. Place a white tile under a conical flask so it’s easier to see the colour change.
3. Place a known volume of one solution into the conical flask using a volumetric pipette. The other solution is placed in the burette with the initial reading on it being noted.
4. Add a few drops of indicator to the conical flask.
5. Open the tap on the burette to add some of the solution to the flask until a permanent colour change is observed. (At this point the flow should be dropwise).
6. Repeat until concordant results are acquired (within 0.1cm^3).