2.4 ACIDS AND REDOX

Question 1

What is the ionic equation of neutralisation?

Answer 1

The ionic equation is always:
H+ + OH- = H2O

Question 2

What do acids release when dissolved in water?

Answer 2

When dissolved in water, acids release hydrogen ions as protons (H+)

Question 3

Strong and weak acids.

Answer 3

Strong acids releases all of its hydrogen atoms into the solution as H+ ions and completely dissociates in aqueous solution.
Weak acids only release a small portion of H+ ions and only partially dissociates.

Question 4

What are bases?

Answer 4

Bases are insoluble in water and are often used to neutralise an acid
- metal oxides
- metal hydroxides
- metal carbonates
- ammonia

Question 5

What are alkalis?

Answer 5

Alkalis are soluble in water and are used to neutralise an acid
- release OH- ions into the solution

Question 6

What is the basic equation when an acid is reacted with an alkali?

Answer 6

Acid + alkali = salt + water

Question 7

What is the basic equation when an acid is reacted with a carbonate?

Answer 7

Acid + carbonate = salt + water + carbon dioxide

Question 8

What is titration used for?

Answer 8

Titration is used for:
- finding the concentration of a solution
- identification of unknown chemicals
- finding the purity of a substance

Question 9

Titration steps.

Answer 9

Steps of titration:
1. weigh carbonate (approx 2.10g) and add to distilled water in 100cm3 beaker
2. add enough distilled water to dissolve the solid, stir with glass rod
3. transfer solution to 250cm3 volumetric flask
4. fill up to the mark with distilled water and invert several times
5. transfer solution to beaker
6. use pipette and pipette filler to transfer 25.0cm3 of solution to 250cm3 conical flask
7. add methyl orange
8. titrate carbonate with hydrochloric acid with constant swirling until colour change is observed (yellow to orange or yellow to pink)
9. repeat until concordant results are reached

Question 10

Calculating titrations.

Answer 10

How to calculate titrations:
1. identify concordant titres and calculate the mean titre
2. balanced symbol equation
3. calculate number of moles in solution with known concentration
4. use stoichiometry to identify the molar ratio
5. use c = n/v to identify the concentration.

Question 11

What is efflorescent and deliquescent?

Answer 11

Efflorescent - loses water
Deliquescent - absorbs water

Question 12

What is a redox reaction?

Answer 12

A redox reaction is:
- a reaction in which oxidation and reduction occur
- OILRIG

Question 13

How to oxidation numbers help identify whether oxidation and reduction has taken place?

Answer 13

Oxidation - increase in oxidation number
Reduction - decrease in oxidation number

Question 14

What is the oxidation number and what are the rules?

Answer 14

Oxidation number is the number of electrons that an atom uses to bond with atoms of another element
1. uncombined element will have an oxidation number of 0
2. oxidation number of an element within a simple ion is the same as the charge of its ion
3. combined oxygen has oxidation number of -2
4. combined hydrogen has oxidation number of +1
5. fluorine has oxidation number of -1
6. sum of oxidation numbers must equal charge on molecule
7. when roman numerals are quoted within the name of the compound they give the oxidation number

Question 15

Oxidation numbers of some elements.

Answer 15

O = -2
H = +1
F = -1
Na+, K+ = +1
Mg2+, Ca2+ = +2
Cl-, Br-, I- + -1
special cases:
H in metal hydrides = -1
O in peroxides = -1
O bonded to F = +2