Chapter 4 Acids and Redox

Question 1

What do all acids contain?

Answer 1

hydrogen -> release H+ ions into the solution when dissolved in water

Question 2

Strong acid

Answer 2

Releases all its hydrogen atoms into solution as H+ ions and completely dissociates in aqueous solution

Question 3

Weak acid

Answer 3

• Releases a small proportion of its available hydrogen atoms into solution as H+ ions
• Partially dissociates in aqueous solution

Question 4

Example of a strong acid

Answer 4

hydrochloric acid

Question 5

Example of a weak acid

Answer 5

Ethanoic acid -> only releases the H on the COOH group

Question 6

Bases

Answer 6

A substance which readily accepts H+ ions

Question 7

Examples of bases

Answer 7

• Metal oxide
• Metal hydroxides
• Metal carbonates

Question 8

Alkali

Answer 8

• A soluble base
• Dissolves in water, releasing OH- ions into the solution

Question 9

Neutralisation

Answer 9

• When the H+ ions (of an acid) react with a base to form a salt and neutral water
• The H+ ions from the acid are replaced by metal or ammonium ions from the base

Question 10

Equations

Answer 10

• Metal + acid -> salt + hydrogen
• Alkali + acid -> water + salt
• Base + acid -> water + salt
• Carbonate + acid -> Water + carbon dioxide + salt

Question 11

Titration

Answer 11

A technique used to accurately measure the volume of 1 solution that reacts exactly with another solution

Question 12

What can titrations be used for?

Answer 12

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

Question 13

Volumetric flask

Answer 13

Used to make up a standard solution very accurately

• come in different sizes

Question 14

Process of preparing a standard solution

Answer 14

1. The solid is weighed accurately
2. Solid is dissolved in a break using a little distilled water
3. This solution is transferred to a volumetric flask
4. The last traces of the solution is rinsed with distilled water
5. The flask is filled up to the graduation line (bottom of meniscus) on the volumetric flask with distilled water
6. The volumetric flask is slowly inverted several times to mix the solution thoroughly

Question 15

What would happen if you didn’t invert the volumetric flask

Answer 15

• Titration results would be inconsistent

Question 16

Apparatus for acid-base titrations

Answer 16

• Pipette
• Burette

Question 17

The acid-base titration procedure

Answer 17

1. Add a measured volume of 1 solution to a conical flask using a pipette
2. Add the other solution to a burette, and take the initial burette reading
3. Add a few drops of an indicator to the conical flask
4. Run the solution in the burette into the conical flask, and continuously swirl it to thoroughly mix the 2 solutions
5. Continue until indicator changes colour = end point
6. Record final burette reading
7. Calculate titre = final burette reading - initial burette reading
8. Repeat until results are concordant

Question 18

The mean titre

Answer 18

• Only use concordant results to keep result accurate

Question 19

Oxidation number

Answer 19

Based on a set of rules that apply to atoms

Question 20

Oxidation number of elements

Answer 20

0

Question 21

Oxidation number for compounds and ions

Answer 21

• Has an oxidation number
• The sign is placed before the number

Question 22

Special cases

Answer 22

• H in metal hydrides
• O in peroxides
• O bonded to F

Question 23

H in metal hydrides

Answer 23

-1

Question 24

O in peroxides

Answer 24

-1

Question 25

O bonded to F

Answer 25

+2

Question 26

Calculating oxidation numbers

Answer 26

Sum of oxidation numbers = total charge

Question 27

Oxidation

Answer 27

* Addition of oxygen * Loss of electrons * Increase in oxidation number

Question 28

Reduction

Answer 28

* Loss of oxygen * Gain of electrons * Decrease in oxidation number

Question 29

Oxidising agent

Answer 29

Facilitates oxidation by being reduces itself

Question 30

Reducing agent

Answer 30

Facilitates reduction by being oxidised itself

Question 31

Redox reactions

Answer 31

A reaction where both reduction and oxidation occur

Question 32

What makes a titre more accurate

Answer 32

* Repeat until results are concordant * Calculate mean titre from results