Exam Cards - Unit 1: Atoms & Reactions

Question 1

Define isotopes.

Answer 1

Atoms of an element with the same number of protons but different numbers of neutrons.

Question 2

Define relative atomic mass (A_r).

Answer 2

The mass of each atom in 1 mole of an element compared to every atom in 1 mole of carbon-12.

Question 3

Define relative isotopic mass.

Answer 3

The mass of each atom in 1 mole of an isotope compared to every atom in 1 mole of carbon-12.

Question 4

Define relative molecular mass (M_r).

Answer 4

The average mass of a molecule compared with one atom of carbon-12.

Question 5

How is the relative molecular mass calculated?

Answer 5

By adding up the relative atomic mass values of all the atoms in the molecule.

Question 6

How is relative atomic mass calculated from isotopic abundances?

Example: 76% of Cl atoms have a relative isotopic mass of 35, while 24% of Cl atoms have a relative isotopic mass of 37. What is the relative atomic mass (A_r)?

Answer 6

1. Multiply each relative isotopic mass by its % relative isotopic abundance and add up the results: (76 x 35) + (24 x 37) = 3548
2. Divide by 100: 3548/100 = 35.5 (1 d.p)

Question 7

What is Avogadro’s Constant?

Answer 7

6.02 x 10²³

Question 8

What is the formula for calculating the number of moles from the number of atoms or molecules?

Answer 8

Number of moles = Number of particles you have/Number of Particles in a mole (N_a)

Example: There are 1.5 x 10²⁴ carbon atoms. How many moles of carbon is this?

Number of moles = 1.5 x 10²⁴/6.02 x 10²³ = 2.49 moles

Question 9

What is molar mass (M) and what is it equal to?

Answer 9

Molar mass is the mass of one mole of something. It is equal to relative molecular mass (M_r).

Question 10

How do you calculate the number of moles using the mass of a substance and molar mass?

Answer 10

Number of moles = mass of substance/ molar mass

n = m/M

Question 11

How do you calculate the number of moles using concentration and volume?

Answer 11

Number of moles = concentration x volume (in dm³)

n = cv

Question 12

How do you calculate the number of moles of a gas at r.tp?

Answer 12

Number of moles = volume in dm³/24

or Number of moles = volume in cm³/24000

Question 13

Define empirical formula.

Answer 13

The smallest whole number ratio of atoms in a compound.

Question 14

Define molecular formula.

Answer 14

The actual numbers of atoms in a molecule.

Question 15

How do you work out the molecular formula of a molecule using the empirical formula?

Example: A molecule has a empirical formula of C₄H₃O₂ and a molecular mass of 166g. Work out the molecular formula.

Answer 15

1. Work out the empirical mass. Example: (4 x 12) + (3 x 1) + (2 x 16) = 83g
2. Divide the molecular mass by the empirical mass. Example: 166/83 = 2 empirical units
3. Multiply the empirical formula by the empirical units. Example: C₄H₃O₂ x 2 = C₈H₆O₄

Question 16

How do you caluculate the empirical formula from experimental results?

Example: When a hydrocarbon is burnt in excess oxygen, 4.4g of carbon dioxide and 1.8g of water are produced. What is the empirical formula of this hydrocarbon?

Answer 16

1. Work out the number of moles of the product. Example: n (CO₂) = 4.4/44 =0.1mol n (H₂O) = 1.8/18 = 0.1mol
2. 1 mol of H₂O contains 2 H atoms, so you must have started with 0.2mol of H atoms
3. C:H = 0.1:0.2
4. Divide by the smallest = 1:2
5. Empirical formula = CH₂

Question 17

How do you work out the empirical formula from percentages?

Answer 17

1. Assume you have 100g of substance so the percentages can be converted t mass
2. Work out the number of moles in each element
3. Divide each number of moles by the smallest number to find a ratio

Question 18

Are acids proton donors or acceptors and why?

Answer 18

Proton donors because they produce H⁺ ions in an aqeuous solution.

Question 19

Are bases proton donors or acceptors and why?

Answer 19

Proton acceptors because they remove H⁺ions from an aqeuous solution.

Question 20

What are the products when an acid reacts with a metal?

Answer 20

Acid + Metal -> Metal Salt + Hydrogen

Question 21

What are the products when an acid reacts with a metal carbonate?

Answer 21

Acid + Metal -> Metal Salt + Carbon Dioxide + Water

Question 22

What is the difference between a hydrated and anhydrous salt?

Answer 22

Hydrated salts contain water of crystallisation and anhydrous salts do not.

Question 23

Define alkali.

Answer 23

A base which dissolves in water.

Question 24

Define oxidation.

Answer 24

The loss of electrons.

Question 25

Define reduction.

Answer 25

The gain of electrons.

Question 26

What term is used for a reaction which has oxidation and reduction happening simultaneously?

Answer 26

A redox reaction.

Question 27

What is the oxidation state for an uncombined element?

Answer 27

0

Question 28

What is the oxidation state for a simple monatomic ion? (e.g. Na⁺)

Answer 28

The oxidation state is equal to its charge (e.g. Na⁺ = 1)

Question 29

What is the oxidation state of compounds or compound ions? (e.g. SO₄^2-)

Answer 29

The oxidation number is the ion charge. (e.g. SO₄^2- = -2)

Question 30

What is the oxidation state for a combined oxygen?

Answer 30

-2 (except in O₂, where it’s 0)

Question 31

What is the oxidation state for a combined hydrogen?

Answer 31

+1 (except in H₂, where it’s 0)

Question 32

What do all ions with the suffix -ate contain?

Answer 32

Oxygen.

Question 33

What is a reducing agent?

Answer 33

Something that donates electrons and gets oxidised.

Question 34

What is a oxidising agent?

Answer 34

Something that accepts electrons and gets reduced.