Module 2: Foundations in Chemistry

Question 1

Define relative molecular mass.

Answer 1

The mass of that specific molecule, relative to the mass of 1/12 of a carbon-12 atom.

Question 2

Define relative atomic mass.

Answer 2

The weighted average mass of an atom of an element taking into account all of its naturally occurring isotopes relative to the mass of 1/12 of a carbon atom.

Question 3

Why is the mass of an atom not proton+neutron+electron?

Answer 3

Due to the strong nuclear force holding protons and neutrons together, some mass is lost, and this is called mass defect.

Question 4

Why are the radii of two isotopes of the same element the same?

Answer 4

They have the same number of protons and electrons.

Question 5

What is the empirical formula of a compound?

Answer 5

The simplest whole number ratio of atoms present in a molecule of a compound.

Question 6

What is the ideal gas equation?

Answer 6

PV=nRT

Question 7

Define oxidation number.

Answer 7

The number of electrons involved in bonding an element to another.

Question 8

What is the oxidation number of an element?

Answer 8

0

Question 9

When is a reaction classified as redox?

Answer 9

In terms of electrons: Electrons are lost and gained

In terms of oxidation numbers: Oxidation numbers increase and decrease

Question 10

What are the oxidation number exceptions?

Answer 10

• Hydrogen in metal hydrides: -1
• Oxygen in peroxides: -1
• Oxygen when bonded to fluorine: +2

Question 11

Define disproportionation.

Answer 11

When a single element is both oxidised and reduced in a reaction.

Question 12

How many electrons does an orbital hold?

Answer 12

Two, which spin in opposite directions.

Question 13

What are the exceptions when writing electron configuration?

Answer 13

1. 4s is filled before 3d, because it has less energy, however it also loses electrons before 3d.
2. For chromium and copper, the 4s sub-shell only has one electron while the 3d sub-shell has five and ten electrons respectively. This is because this is more stable.

Question 14

What is the shape of an S sub-shell and a P sub-shell?

Answer 14

• S: Spherical
• P: Dumbbell shaped

Question 15

Which elements don’t follow the octet rule?

Answer 15

1. 8 > Boron
2. 8 < Sulfur

Question 16

Define coordinate / dative covalent bonding.

Answer 16

When one atom provides both electrons in a covalent bond.

Question 17

How does solubility change as ionic charge increases?

Answer 17

It decreases.

Question 18

Are metals soluble in water?

Answer 18

No, they don’t dissolve, they react.

Question 19

What shape and angle does a molecule with 0 LPs and 2 BPs have?

Answer 19

Shape: Linear
Angle: 180

Question 20

What shape and angle does a molecule with 0 LPs and 3 BPs have?

Answer 20

Shape: Trigonal planar
Angle: 120

Question 21

What shape and angle does a molecule with 1 LPs and 2 BPs have?

Answer 21

Shape: Non-linear
Angle: 119

Question 22

What shape and angle does a molecule with 0 LPs and 4 BPs have?

Answer 22

Shape: Tetrahedral
Angle: 109.5

Question 23

What shape and angle does a molecule with 1 LPs and 3 BPs have?

Answer 23

Shape: Trigonal pyramidal
Angle: 107

Question 24

What shape and angle does a molecule with 2 LPs and 2 BPs have?

Answer 24

Shape: Non-linear
Angle: 104.5

Question 25

What shape does a molecule with 0 LPs and 5 BPs have?

Answer 25

Shape: Trigonal bipyramidal

Question 26

What shape does a molecule with 0 LPs and 6 BPs have?

Answer 26

Shape: Octahedral

Question 27

Define electronegativity.

Answer 27

An atom's ability to attract the **electron density** in a covalent bond to itself.

Question 28

Define bond polarity.

Answer 28

Difference in electronegativity between two bonded atoms.

Question 29

What is a dipole and when does a molecule have permanent dipole?

Answer 29

A dipole is the difference in charge as a result of bond polarity and a molecule had a permanent dipole when the **charges don't cancel out**.

Question 30

What are the three types of intermolecular forces?

Answer 30

1. Induced dipole-dipole interactions (London forces) 2. Permanent dipole-dipole interactions 3. Hydrogen bonds

Question 31

What types of bonds result in hydrogen bonds

Answer 31

1. O-H 2. N-H 3. F-H

Question 32

What modifications can be made to the method of an experiment where you are trying to find the water of crystalisation to make it more accurate?

Answer 32

-Use a greater mass of hydrated salt -Use a scale with a higher resolution -Keep heating until mass no longer changes

Question 33

What is an acid?

Answer 33

Proton donor

Question 34

What is a base?

Answer 34

Proton acceptor

Question 35

What is an alkali?

Answer 35

Water soluble base, releases hydroxide ions in water

Question 36

What is the difference between a strong acid and a weak acid?

Answer 36

A strong acid fully dissociates, while a weak acid partially dissociates

Question 37

What does amphoteric mean?

Answer 37

Something that can behave as an acid or a base

Question 38

What are the uses of titration?

Answer 38

- Finding concentration of solution - Identification of unknown solution - Finding the purity of a substance

Question 39

What is a standard solution?

Answer 39

A solution of known concentration

Question 40

What are concordant titres?

Answer 40

Titres with 0.1cm⁻³ of each other

Question 41

Why is it important to fill the space below the tap in the burette before beginning an accurate titration?

Answer 41

It will fill during titration and cause titre to be too high and appear to have more moles of acid.

Question 42

Why does rinsing the inside of the conical flask with water improve the accuracy of each titre?

Answer 42

Ensures no solution is lost / ensures all reagents are in the reaction mixture.

Question 43

What indicators are used in titrations?

Answer 43

Phenolphthalein: Pink in strong alkalis, colourless once neutralised Methyl orange: Orange in strong acids, colourless when neutralised