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

Answer 3

They have the same number of protons and electrons.

Question 4

What is the empirical formula of a compound?

Answer 4

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

Question 5

What is the ideal gas equation?

Answer 5

PV=nRT

Question 6

Define oxidation number.

Answer 6

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

Question 7

What is the oxidation number of an element?

Answer 7

0

Question 8

When is a reaction classified as redox?

Answer 8

In terms of electrons: Electrons are lost and gained

In terms of oxidation numbers: Oxidation numbers increase and decrease

Question 9

What are the oxidation number exceptions?

Answer 9

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

Question 10

Define disproportionation.

Answer 10

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

Question 11

How many electrons does an orbital hold?

Answer 11

Two, which spin in opposite directions.

Question 12

What are the exceptions when writing electron configuration?

Answer 12

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 13

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

Answer 13

• S: Spherical
• P: Dumbbell shaped

Question 14

Which elements don’t follow the octet rule?

Answer 14

1. 8 > Boron
2. 8 < Sulfur

Question 15

Define coordinate / dative covalent bonding.

Answer 15

When one atom provides both electrons in a covalent bond.

Question 16

How does solubility change as ionic charge increases?

Answer 16

It decreases.

Question 17

Are metals soluble in water?

Answer 17

No, they don’t dissolve, they react.

Question 18

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

Answer 18

Shape: Linear
Angle: 180

Question 19

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

Answer 19

Shape: Trigonal planar
Angle: 120

Question 20

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

Answer 20

Shape: Non-linear
Angle: 119

Question 21

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

Answer 21

Shape: Tetrahedral
Angle: 109.5

Question 22

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

Answer 22

Shape: Trigonal pyramidal
Angle: 107

Question 23

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

Answer 23

Shape: Non-linear
Angle: 104.5

Question 24

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

Answer 24

Shape: Trigonal bipyramidal

Question 25

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

Answer 25

Shape: Octahedral

Question 26

Define electronegativity.

Answer 26

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

Question 27

Define bond polarity.

Answer 27

Difference in electronegativity between two bonded atoms.

Question 28

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

Answer 28

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 29

What are the three types of intermolecular forces?

Answer 29

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

Question 30

What types of bonds result in hydrogen bonds

Answer 30

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

Question 31

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 31

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

Question 32

What is an acid?

Answer 32

Proton donor

Question 33

What is a base?

Answer 33

Proton acceptor

Question 34

What is an alkali?

Answer 34

Water soluble base, releases hydroxide ions in water

Question 35

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

Answer 35

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

Question 36

What does amphoteric mean?

Answer 36

Something that can behave as an acid or a base

Question 37

What are the uses of titration?

Answer 37

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

Question 38

What is a standard solution?

Answer 38

A solution of known concentration

Question 39

What are concordant titres?

Answer 39

Titres with 0.1cm³ of each other

Question 40

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

Answer 40

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

Question 41

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

Answer 41

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

Question 42

What indicators are used in titrations?

Answer 42

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

Question 43

Why should solutions containing salts be allowed to evaporate rather than boiling off the water?

Answer 43

When the solution evaporates, a hydrated crystal forms, when it's boiled, an anhydrous salt forms