Module 2: Chapter 4 - Acids and Redox

Question 1

What are concordant results?

Answer 1

Results within 0.10 cm³ of each other

Question 2

What is the general ionic equation for a precipitation reaction?

Answer 2

Aqueaous Ions (aq) -> insoluble solid (s)

Question 3

What is a precipitation reaction?

Answer 3

A reaction between soluble ions which form an insoluble solid known as a precipitate

Question 4

What is the general ionic equation for a neutralisation reaction beween an acid and an alkali?

Answer 4

H⁺ (aq) + OH⁻ (aq) -> H₂O(l)

Question 5

What is the general ionic equation for a neutralisation reaction beween an acid and a carbonate?

Answer 5

2H⁺ (aq) + CO₃²⁻ (aq) -> H₂O (l) + CO₂ (g)

Question 6

What is the general ionic equation for a neutralisation reaction beween an acid and a hydrogencarbonate?

Answer 6

H⁺ (aq) + HCO₃⁻ (aq) -> H₂O (l) + CO₂ (g)

Question 7

What is hydrogencarbonate (HCO₃⁻) more commonly known as?

Answer 7

Bicarbonate

Question 8

What is a strong acid?

Answer 8

An acid that releases all its hydrogen atoms into solution as H⁺ ions and completely dissociates in aqueous solution.

Question 9

What is a weak acid?

Answer 9

An acid that only releases a small proportion of its available hydrogen atoms into solution as H⁺ ions. It partially dissociates in aqueous solution.

Question 10

What is the equation for ethanoic acid dissociating?

Answer 10

all state symbols should be (aq)

Question 11

What is a base?

Answer 11

A substance which neutralises an acid to form a salt

Question 12

What are the types of bases?

Answer 12

• Metal oxides
• Metal hydroxides
• Metal carbonates
• Ammonia solution

Question 13

What is an alkali?

Answer 13

A base that dissolves in water, releasing hydroxide ions into the solution

Question 14

How do you name a salt from a neutralisation reaction?

Answer 14

The start of the name comes from the base, the ending comes from the aci8d

Question 15

Sulfuric acid is a strong acid, explain why it does not dissociate as expected.

Answer 15

H₂SO₄ is a strong acid, therefore it first dissociates by the following equation:
H₂SO₄ (aq) -> H⁺ (aq) + HSO₄⁻(aq).
However, the resulting HSO₄⁻ ion is a weak acid and therefore dissociates by the following equation:
HSO₄⁻(aq) ⇌ H⁺ (aq) + SO₄²⁻(aq)

Question 16

What are the equations for sulfuric acid dissociating?

Answer 16

1. H₂SO₄ (aq) -> H⁺ (aq) + HSO₄⁻(aq)
2. HSO₄⁻(aq) ⇌ H⁺ (aq) + SO₄²⁻(aq)

Question 17

Is phosphoric acid a strong acid or a weak acid?

Answer 17

A strong acid

Question 18

What are the equations for phosphoric acid ionising?

Answer 18

Question 19

What is titration?

Answer 19

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

Question 20

What can titration be used for?

Answer 20

• Finding the concentration of solution
• Identification of unknown chemicals
• Finding the purity of a substance

Question 21

What is a burette reading to?

Answer 21

Always to 2 decimal points, ending in a 5 or a 0 as it is measured to the nearest half division

Question 22

What colour is phenolphtalein in an alkaline solution?

Answer 22

Pink/Purple

Question 23

What colour is phenolphtalein in a neutral solution?

Answer 23

Colourless

Question 24

What colour is phenolphtalein in an acidic solution?

Answer 24

Colourless

Question 25

What colour is methyl orange in an alkaline solution?

Answer 25

Yellow

Question 26

What colour is methyl orange in a neutral solution?

Answer 26

Orange

Question 27

What colour is methyl orange in an acidic solution?

Answer 27

Red

Question 28

Answer 28

n = 1

Question 29

What is the equation for % uncertainty?

Answer 29

(number of readings x uncertainty) / reading

Question 30

What is the oxidation state/number?

Answer 30

A measure of the number of electrons that an atom uses to bond with atoms of another element.

Question 31

What are the rules for assigning oxidation states?

Answer 31

* On simple ions, the oxidation state is the charge on the ion * In elements, the oxidation number is 0 * The total of the oxidation states must equal to the overall charge on the species * In molecules and more complex ions, the more electronegative element is assumed to be the negative ion (meaning a normally negative ion can have a positive oxidation number) * H is **nearly** always +1 and oxygen -2 * Fluorine is always -1

Question 32

When is the oxidation number of H not +1?

Answer 32

When bonded with metals or Boron, the oxidation number is then -1

Question 33

When is the oxidation number of O not -2?

Answer 33

When bonded with Fluorine (where it is +2) or in H2O2 (where it is -1)

Question 34

What is oxidation?

Answer 34

* The gain of oxygen * The loss of electrons * Increase in oxidation number

Question 35

What is reduction?

Answer 35

* The loss of oxygen * The gain of electrons * Decrease in oxidation number

Question 36

What happens to the oxidation number when something is oxidised?

Answer 36

The oxidation number increases

Question 37

What happens to the oxidation number when something is reduced?

Answer 37

The oxidation number decreases

Question 38

How can you use oxidation numbers to determine whether a reaction is redox or not?

Answer 38

Identify all the oxidation numbers of products and reactants. Use these to see if any atoms have gained electrons (reduced) or lost electrons (oxidation). If there has been both a reduction and an oxidation reaction then it is a redox reaction

Question 39

What is a disproportionation reaction?

Answer 39

A disproportionation reaction is a redox reaction in which the same element is both oxidised and reduced

Question 40

What is the oxidising agent?

Answer 40

A reagent that oxidises another species by taking electrons from them and is therefore reduced itself

Question 41

What is the reducing agent?

Answer 41

A reagent that reduces another species by adding electrons to it and is therefore oxidised itself

Question 42

How do you write a half equation?

Answer 42

1. Calculate the oxidation states on each side of the equation 2. Balance the element changing oxidation state 3. Balance electrons in respect to changing oxidation states (always do +e) 4. Sort out O's, for every O gained/lost add an H₂O molecule 5. Sort out H's, for every H gained/lost add an H⁺ ion 6. Check to see if the total electric charge on the left is equal to the total electric charge on the right

Question 43

Write the half equation for: Cr₂O₇²⁻ -> Cr³⁺

Answer 43

Cr₂O₇²⁻ + 6e⁻ + 14H⁺ -> 2Cr³⁺ + 7H₂O

Question 44

Write the half equation for: N₂ -> NO₃⁻

Answer 44

N₂ + 6H₂O -> 2NO₃⁻ + 10e⁻ + 12H⁺

Question 45

Write the half equation for: S₂O₃²⁻ -> S

Answer 45

S₂O₃²⁻ + 4e⁻ + 6H⁺-> 2S + 3H₂O

Question 46

Write equations for the partial and complete neutralisation reactions of carbonic acid (H₂CO₃) with sodium hydroxide

Answer 46

Partial: NaOH(aq) + H₂CO₃(aq) -> NaHCO₃(aq) + H₂O(l) Complete: 2NaOH(aq) + H₂CO₃(aq) -> NaCO₃(aq) + 2H₂O(l)

Question 47

Why is sodium hydrogencarbonate known as an acid salt?

Question 48

## Footnote HARD QUESTION

Answer 48

The Mn in MnO₄⁻ has an oxidation state of 7+ and Mn²⁺ has an oxidation state of 2+, therefore there is a change of 5 electrons. If we have 8 moles of MnO₄⁻ then it is a change of 40 electrons. 5 Moles of N₂O₂²⁻ contrains 10 moles of N, therefore the oxidation number of each N changes by 4 electrons. Since the oxidation number of N in N₂O₂²⁻ is 1+, the new oxidation number must be 5+. Therefore the second product of the reaction is NO₃⁻

Question 49

Use oxidation states to determine the molar ratio in which these species react: MnO₄⁻ reacts with SO₃²⁻ to Form Mn²⁺ and SO₄²⁻

Answer 49

2:5

Question 50

Use oxidation states to determine the molar ratio in which these species react: Cr₂O₇²⁻ reacts with Fe²⁺ to form Cr³⁺ and Fe³⁺

Answer 50

1:6

Question 51

Where is the sign placed in the oxidation number?

Answer 51

Before the number, ie -1, +3, -5

Question 52

How are roman numerals used in respect to oxidation numbers?

Answer 52

Roman numerals are used in the names of compounds of elements that form ions with different charges. The roman numeral shows the oxidation number of the element (without a +- sign). i.e. Iron (II) represents Fe²⁺, Nitrate (III) represents NO₂⁻

Question 53

What is the modern name of nitrite (NO₂⁻)?

Answer 53

Nitrate (III)

Question 54

What is the modern name of nitrate (NO₃⁻)

Answer 54

Nitrate (V)

Question 55

Can oxidation or reduction takes place alone?

Answer 55

No, for one to occur they must both occur. Therefore, they always occur in a redox reaction