Module 2: Chapter 4 - Acids and Redox Flashcards
What are concordant results?
Results within 0.10 cm³ of each other
What is the general ionic equation for a precipitation reaction?
Aqueaous Ions (aq) -> insoluble solid (s)
What is a precipitation reaction?
A reaction between soluble ions which form an insoluble solid known as a precipitate
What is the general ionic equation for a neutralisation reaction beween an acid and an alkali?
H⁺ (aq) + OH⁻ (aq) -> H₂O(l)
What is the general ionic equation for a neutralisation reaction beween an acid and a carbonate?
2H⁺ (aq) + CO₃²⁻ (aq) -> H₂O (l) + CO₂ (g)
What is the general ionic equation for a neutralisation reaction beween an acid and a hydrogencarbonate?
H⁺ (aq) + HCO₃⁻ (aq) -> H₂O (l) + CO₂ (g)
What is hydrogencarbonate (HCO₃⁻) more commonly known as?
Bicarbonate
What is a strong acid?
An acid that releases all its hydrogen atoms into solution as H⁺ ions and completely dissociates in aqueous solution.
What is a weak acid?
An acid that only releases a small proportion of its available hydrogen atoms into solution as H⁺ ions. It partially dissociates in aqueous solution.
What is the equation for ethanoic acid dissociating?
all state symbols should be (aq)
What is a base?
A substance which neutralises an acid to form a salt
What are the types of bases?
- Metal oxides
- Metal hydroxides
- Metal carbonates
- Ammonia solution
What is an alkali?
A base that dissolves in water, releasing hydroxide ions into the solution
How do you name a salt from a neutralisation reaction?
The start of the name comes from the base, the ending comes from the aci8d
Sulfuric acid is a strong acid, explain why it does not dissociate as expected.
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)
What are the equations for sulfuric acid dissociating?
- H₂SO₄ (aq) -> H⁺ (aq) + HSO₄⁻(aq)
- HSO₄⁻(aq) ⇌ H⁺ (aq) + SO₄²⁻(aq)
Is phosphoric acid a strong acid or a weak acid?
A strong acid
What are the equations for phosphoric acid ionising?
What is titration?
A technique used to accurately measure teh volume of one solution that reacts exactly with another solution
What can titration be used for?
- Finding the concentration of solution
- Identification of unknown chemicals
- Finding the purity of a substance
What is a burette reading to?
Always to 2 decimal points, ending in a 5 or a 0 as it is measured to the nearest half division
What colour is phenolphtalein in an alkaline solution?
Pink/Purple
What colour is phenolphtalein in a neutral solution?
Colourless
What colour is phenolphtalein in an acidic solution?
Colourless
What colour is methyl orange in an alkaline solution?
Yellow
What colour is methyl orange in a neutral solution?
Orange
What colour is methyl orange in an acidic solution?
Red
n = 1
What is the equation for % uncertainty?
(number of readings x uncertainty) / reading
What is the oxidation state/number?
A measure of the number of electrons that an atom uses to bond with atoms of another element.
What are the rules for assigning oxidation states?
- 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
When is the oxidation number of H not +1?
When bonded with metals or Boron, the oxidation number is then -1
When is the oxidation number of O not -2?
When bonded with Fluorine (where it is +2) or in H2O2 (where it is -1)
What is oxidation?
- The gain of oxygen
- The loss of electrons
- Increase in oxidation number
What is reduction?
- The loss of oxygen
- The gain of electrons
- Decrease in oxidation number
What happens to the oxidation number when something is oxidised?
The oxidation number increases
What happens to the oxidation number when something is reduced?
The oxidation number decreases
How can you use oxidation numbers to determine whether a reaction is redox or not?
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
What is a disproportionation reaction?
A disproportionation reaction is a redox reaction in which the same element is both oxidised and reduced
What is the oxidising agent?
A reagent that oxidises another species by taking electrons from them and is therefore reduced itself
What is the reducing agent?
A reagent that reduces another species by adding electrons to it and is therefore oxidised itself
How do you write a half equation?
- Calculate the oxidation states on each side of the equation
- Balance the element changing oxidation state
- Balance electrons in respect to changing oxidation states (always do +e)
- Sort out O’s, for every O gained/lost add an H₂O molecule
- Sort out H’s, for every H gained/lost add an H⁺ ion
- Check to see if the total electric charge on the left is equal to the total electric charge on the right
Write the half equation for:
Cr₂O₇²⁻ -> Cr³⁺
Cr₂O₇²⁻ + 6e⁻ + 14H⁺ -> 2Cr³⁺ + 7H₂O
Write the half equation for:
N₂ -> NO₃⁻
N₂ + 6H₂O -> 2NO₃⁻ + 10e⁻ + 12H⁺
Write the half equation for:
S₂O₃²⁻ -> S
S₂O₃²⁻ + 4e⁻ + 6H⁺-> 2S + 3H₂O
Write equations for the partial and complete neutralisation reactions of carbonic acid (H₂CO₃) with sodium hydroxide
Partial: NaOH(aq) + H₂CO₃(aq) -> NaHCO₃(aq) + H₂O(l)
Complete: 2NaOH(aq) + H₂CO₃(aq) -> NaCO₃(aq) + 2H₂O(l)
Why is sodium hydrogencarbonate known as an acid salt?
HARD QUESTION
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⁻
Use oxidation states to determine the molar ratio in which these species react:
MnO₄⁻ reacts with SO₃²⁻ to Form Mn²⁺ and SO₄²⁻
2:5
Use oxidation states to determine the molar ratio in which these species react:
Cr₂O₇²⁻ reacts with Fe²⁺ to form Cr³⁺ and Fe³⁺
1:6
Where is the sign placed in the oxidation number?
Before the number, ie -1, +3, -5
How are roman numerals used in respect to oxidation numbers?
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⁻
What is the modern name of nitrite (NO₂⁻)?
Nitrate (III)
What is the modern name of nitrate (NO₃⁻)
Nitrate (V)
Can oxidation or reduction takes place alone?
No, for one to occur they must both occur. Therefore, they always occur in a redox reaction
