CHAPTER 4: ACIDS AND REDOX

Question 1

What are acids?

Answer 1

Proton donors that release H+ ions in aqueous solution.

Question 2

What are alkalis?

Answer 2

Proton acceptors that release OH– ions in aqueous solution.

Question 3

What are common acids?

Answer 3

• Hydrochloric acid, HCl
• Sulphuric acid, H2SO4
• Nitric acid, HNO3
• Ethanoic acid, CH3COOH

Question 4

What are common alkalis?

Answer 4

• Sodium hydroxide, NaOH
• Potassium hydroxide, KOH
• Ammonia, NH3

Question 5

What is a strong acid?

Answer 5

Strong acids fully dissociate, and protons are easily lost.

Question 6

What is a weak acid?

Answer 6

Weak acids only partially dissociate, and protons are not easily lost.

Question 7

What is a strong base?

Answer 7

Strong bases fully dissociate, and hydroxide ions are easily lost.

Question 8

What is a weak base?

Answer 8

Weak bases only partially dissociate, and hydroxide ions are not easily lost.

Question 9

What is the method for titration?

Answer 9

1. A measured volume of x is added to a conical flask using a pipette, along with a suitable indicator to the flask, e.g. phenolphthalein, methyl orange
2. The burette is filled with the other solution, y, which is of a known concentration
3. A small quantity of y flows into the flask with x. This is allowed to occur until the end point is reached, indicated by a colour change
4. The volume of y that has been added is measured and unknowns can then be calculated

Question 10

What is a standard solution?

Answer 10

Standard solutions are solutions of a known concentration.

Question 11

What is the method for a standard solution?

Answer 11

1. A known mass of the solute is dissolved in
   a chosen solvent in a beaker
2. The solution is transferred into a volumetric flask. Several washings are also made and transferred to the volumetric flask
3. More solvent is added to the volumetric flask until the level is nearly at the graduation line
4. The solvent is then added drop by drop until the bottom of the meniscus is sitting on the graduation line. Do not allow the solution to fill above the line
5. The volumetric flask is sealed and the solution mixed thoroughly by inverting it multiple times

Question 12

What is neutralisation?

Answer 12

acid + base ➡️ salt + water

H+ +OH- ➡️ H2O

Question 13

What are salts?

Answer 13

Salts are ionic compounds in which the H+ ion of an acid has been replaced by a metal ion or another positive ion. Salts are made up of a cation — the positive ion, usually a metal ion or ammonium ion and an anion — the negative ion, usually derived from an acid.

Question 14

What an acid and an alkali make?

Answer 14

acid + base ➡️ salt + water

Question 15

What does an acid and a metal make?

Answer 15

acid + metal ➡️ salt + hydrogen (gas)

Question 16

What does a metal oxide and an acid make?

Answer 16

acid + metal oxide ➡️ salt + water

Question 17

What does an acid and a metal carbonate make?

Answer 17

acid + metal ➡️ salt + water + carbon dioxide

Question 18

What is oxidation and reduction?

Answer 18

Oxidation is gain of electrons and reduction is loss of electrons.

Question 19

What is an oxidation number?

Answer 19

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

Question 20

What are the rules of oxidation?

Answer 20

• An element has an oxidation number of 0
• A simple ion (of a single element) has an oxidation number equal to the charge on the ion
• The sum of oxidation numbers of the elements in a compound is equal to the overall charge of the compound
• The charge on a complex ion, e.g. NH4+, is equal to the sum of the oxidation numbers
• The most electronegative element in a compound always has a negative oxidation number

Question 21

What is an oxidising agent?

Answer 21

• Cause oxidation of other species,
and so are themselves reduced
• Reduction is the gain of
electrons — oxidising agents gain electrons

Question 22

What is a reducing agent?

Answer 22

• Cause reduction of other species,
and so are themselves oxidised
• Oxidation is the loss of electrons — reducing agents donate electrons