Chapter 4 (2.1.4/5)

Question 1

Rules of oxidation numbers

Answer 1

• always 0 for elements
• in a pure element, bonding is to atoms of the same element
• each atom in a compound has an oxidation number
• number has a sign placed before it
• numerically the same as the ions charge, some exceptions
• sum of oxidation numbers = total charge

Question 2

Special cases for oxidation numbers

Answer 2

• H in metal hydrides: -1
• O in peroxides: -1
• O bonded to F: +2

Question 3

Roman numerals

Answer 3

• indicate magnitude of oxidation number when an element may have compounds/ions with different oxidation numbers

Question 4

Oxidation

Answer 4

• addition of oxygen
• loss of electrons
• increase in oxidation number

Question 5

Reduction

Answer 5

• removal of oxygen
• gain of electrons
• decrease in oxidation number

Question 6

What is a salt?

Answer 6

When the H+ ion in an acid is replaced by a metal ion or an ammonium ion.

Question 7

Define an acid

Answer 7

Proton donor

Question 8

Define a base

Answer 8

Proton acceptor

Question 9

Formula of common acids: hydrochloric, sulfuric, nitric, ethanoic

Answer 9

• HCl
• H2SO4
• NO3
• CH3COOH

Question 10

Formula of common bases: sodium hydroxide, potassium hydroxide, ammonia

Answer 10

• NaOH
• KOH
• NH3

Question 11

What happens when acids dissolve in water?

Answer 11

They release H+ ions into the aqueous solution

Question 12

What happens when an alkali dissolves in water?

Answer 12

They release OH- ions into the aqueous solution

Question 13

What is an alkali?

Answer 13

A water-soluble base

Question 14

What is a strong acid?

Answer 14

A strong acid releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution

Question 15

What is a weak acid?

Answer 15

A weak acid only releases a small proportion of its available hydrogen atoms into solution as H+ ions and partially dissociates in aqueous solution. (double arrow used in equations)

Question 16

Name general examples of bases

Answer 16

• metal oxides
• metal hydroxides
• metal carbonates
• ammonia

Question 17

Neutralisation reaction

Answer 17

H+ (aq) + OH- (aq) –> H2O (l)

Question 18

General equations for neutralisation of acids

Answer 18

acid + metal oxide/hydroxide –> salt + water
acid + alkali –> salt + water
acid + metal carbonate –> salt + water + carbon dioxide
acid + metal –> salt + hydrogen

Question 19

How do you prepare a standard solution?

Answer 19

1. accurately weigh solid
2. dissolve in distilled water
3. transfer to volumetric flask
4. add more distilled water to graduation line
5. slowly invert flask several times to mix

Question 20

Percentage uncertainty formula

Answer 20

uncertainty/capacity X 100

Question 21

Percentage purity formula

Answer 21

mass of pure/mass of impure X 100

Question 22

Describe a titration

Answer 22

1. add a measured volume of unknown concentration solution to a conical flask using a pipette
2. add solution of known concentration to burette and record initial reading
3. add a few drops of indicator
4. run solution and swirl the flask. stop at endpoint
5. record final reading and calculate titre
6. using the rough titre, repeat the titration but now adding solution in a dropwise manner as endpoint is approached. repeat until 2 concordant results are obtained.

Question 23

What is a disproportionation reaction?

Answer 23

A reaction in which the same element is reduced and oxidised