Chapter 13 - Acids And Bases

Question 0

Properties of bases

Answer 0

• Taste bitter
• Feel slippery
• Cause indicators to change colour eg. Red litmus changes to blue
• Can be corrosive
• Do not react with most metals
• Many solutions of bases conduct electricity
• React with acids to form water

Question 1

Properties of acids

Answer 1

• Taste sour
• Cause indicators change colour eg. blue litmus to red
• Are corrosive
• Many solutions of acids conduct electricity
• React with carbonates eg. marble, and hydrogen carbonates to form CO2 and water
• React with some metals to form hydrogen
• React with bases to form water

Question 2

Explain the Arrhenius theory of acids and bases

Answer 2

Was proposed by Svante Arrhenius in 1883. He suggested that
- an acid has H in its formula and dissolves in water to form hydrogen
ions, H+(aq)
- a base has OH in its formula and when added to water forms
hydroxide ions, OH-(aq)

Question 3

Use the Arrhenius theory to explain the ionisation of HCL when added to water, and the dissociation of NaOH when added to water

Answer 3

HCL(g) —> H+(aq) + Cl-(aq)

NaOH(s) —> Na+(aq) + OH-(aq)

Question 4

Use the Arrhenius theory to explain the properties of acids and bases

Answer 4

• Because all acids have H+ in their solution, they all react with carbonates, hydrogen-carbonates, and metals.
• Solutions of acids can conduct electricity because of the H+ ions the negative ions present in the solution
• When mixed together, an acid and a base undergo neutralisation, occurring because the H+ ions from the acid react with the OH- ions from the base to form water, which, according to the Arrhenius theory, is neither an acid or a base

Question 5

Explain the limitations to the Arrhenius theory

Answer 5

• Some substances that behave as bases, that is produce OH- ions in solution, do not contain OH in their formula, eg. ammonia and the carbonate ion
• The theory only applies to solutions of acids and bases in water and not in other solvents
• The hydrogen ion H+ cannot exist in water for very long. It reacts with water to form H3O+ the hydronium ion

Question 6

Explain the Brønsted-Lowry theory of acids and bases

Answer 6

An acid-base reaction is one that involves the transfer of a hydrogen ion (a proton) from one reactant to another. The reactant that loses the hydrogen ion is called the acid and the reactant that gains the hydrogen ion is the base. According to the B/L theory, when hydrogen chloride molecules are dissolved in water, each hydrogen chloride molecule donates a hydrogen ion to a water molecules. The HCl acts as a B/L acid and the the water acts as a B/L base.

Question 7

Rephrase the definition of a Brønsted-Lowry acid and base:

Answer 7

• Acids: are proton donors

- Bases: are proton acceptors

Question 8

What is a limitation of the Brønsted-Lowry theory

Answer 8

Since it defines an acid as being a hydrogen ion donor, it excludes substances that have no hydrogen ions to donate from being classified as acids.

Question 9

Explain water as an amphoteric substance

Answer 9

Water is capable of accepting or donating a hydrogen ion,model ending on whether it is reacting with an acid or a base. This is why it is an amphoteric substance, because it can act as either an acid or a base.
Because it is amphoteric, one water molecule can react with another water molecule in an acid-base reaction, as shown in the equation:
H2O + H2O H3O+(aq) + OH-(aq)
This reaction is called the self-ionisation of water

Question 10

Explain conjugate acids and bases

Answer 10

When a Brønsted-Lowry acid reacts by losing a hydrogen ion, the species it forms has the potential to act as a base. For example, when HCl loses a hydrogen ion to a base it forms Cl-. This Cl- can, under certain conditions, act as a base by gaining a hydrogen ion from an acid to form HCl. An acid and the base it forms when it loses a hydrogen ion are called a conjugate acid-base pair.

Question 11

What does a reaction between an acid and a base produce?

Answer 11

A salt + water

Question 12

What does a reaction between an acid and a carbonate produce?

Answer 12

Carbon dioxide, water and a salt

Question 13

What does a reaction between an acid and a metal produce?

Answer 13

Hydrogen + a salt

Question 14

What is a strong acid according to the Arrhenius theory?

Answer 14

When a strong acid is dissolved in water, all the acid molecules break up into hydrogen ions and negative ions. E.g. If 1 mol of HCl is dissolved in water, then 1 mol of H+ ions and 1 mol of Cl- ions are formed. No HCl molecules remain in the solution

Question 15

What is a weak acid according to the Arrhenius theory?

Answer 15

When a weak acid is added to water, only some of the molecules are ionised. E.g. If 1 mol of hydrogen fluoride molecules is dissolved in 1L of water, only approximately 0.03 mol of the molecules are ionised.

Question 16

What can be used to determine if an acid or a base is strong/weak. How?

Answer 16

Electrical conductivity can be used. A solution that contains a large concentration of ions conducts electricity much better than a solution containing a smaller concentration of ions.

Question 17

What is monoprotic?

Answer 17

It means that each molecule of an acid produces only one hydrogen ion during the ionisation process in aqueous solution.

Question 18

What does polyprotic acid mean?

Answer 18

Acids that produce more than one hydrogen ion when they dissolve in water.

Question 19

What does a reaction between an acid and a metal hydroxide produce?

Answer 19

Water and a salt solution

Question 20

What does a reaction between an acid and a metal oxide produce?

Answer 20

Water and a salt solution

Question 21

What does a reaction between an acid and a metal hydrogencarbonate produce?

Answer 21

Carbon dioxide + water + salt solution

Question 22

What does a reaction between an acid and a metal carbonate produce?

Answer 22

Carbon dioxide + water + salt solution

Question 23

Explain pH.

• in neutral solutions
• in acidic solutions
• in basic solutions

Answer 23

In neutral solutions, such as water:
- concentration of H3O+ = concentration of OH- = 1x10(-7)molL-1
In acidic solutions:
- concentration of H3O+ is greater than 1x10(-7)molL-1
In basic solutions:
- concentration of OH- is greater than 1x10(-7)molL-1

Question 24

How is the pH. of an aqueous solution is defined as?

Answer 24

pH. = -log(concentration of H+)

Question 25

How can the relationship between pH and the conc. of H+ be represented?

Answer 25

If concentration of H+ = 10(-x) then pH = x

Question 26

Give the pH of:

• pure water
• 0.1 molL-1 HCl
• 1 molL-1 CH3COOH

Answer 26

• is 10(-7) molL-1, so pH is 7
• is 10(-1) molL-1, so pH is 1
• is approx. 10(-3), so pH is approx. 3

Question 27

Explain basic oxides

Answer 27

All basic oxides are metal oxides.
If a metal oxide is soluble in water, it reacts with the water to form hydroxide ions.
The pH of the solution is greater than 7
CaO(s) + H2O -> Ca2+(aq) + 2OH-(aq)
Basic oxides will react with acids to form water and salt solutions

Question 28

Explain acidic oxides

Answer 28

Most acidic oxides are non-metal oxides.
If an acidic oxide is soluble in water, it reacts with the water to form a hydroxy compound which is an acid. This acid produces hydrogen ions in solution.
The pH is less than 7

Question 29

Explain amphoteric oxides.

Answer 29

React with both acids and bases.
Water and a salt solution are formed when amphoteric oxides react with an acid.
I’m the reaction of an amphoteric oxide with a solution containing OH- ions, an ion composed of two different ions, the metal ion and OH- ion, is formed. This type of ion is called a complex ion.

Question 30

Explain neutral oxides

Answer 30

The neutral oxides are all nonmetallic oxides and they display no acid/base properties. They form neutral solutions when dissolved in water and they do not react with acids or bases.