O3

Question 1

What is a buffer solution?

Answer 1

A solution which minmises pH changes on addition of small amounts of acid and base

Question 2

What is a buffer solution a mixture of?

Answer 2

A weak acid + its conjugate base
OR
A weak acid + it’s salt

Question 3

Explain how a buffer solution works?

Answer 3

• adding acid moves equilibrium to the left - removing H+
  Adding alkali moves the equilibrium to the right - producing H+ to replace H+ ions removed by forming H2O with OH-
  Has large amounts of HA and A- so H+ concentration hardly changes

Question 4

What is Ka when there are equal amounts of [HA] and [A-]?

Answer 4

Ka = H+

Question 5

What does the pH of the buffer solution depend on?

Answer 5

• The value of Ka
• ratio of [salt] : [weak acid]

Question 6

What is the Ka equation for a buffer?

Answer 6

Ka = [H+] [A-] / [HA]

Question 7

MODEL ANSWER : greenhouse effect

Answer 7

Radiation from the sun reaches the Earth
It is made up of visible and UV radiation
The Earth absorbs some of the solar radiation
The Earth warms up
The warm earth emits infrared radiation
Greenhouse gases include carbon dioxide and methane
They are present in the troposphere
These gases absorb infrared radiation
This increases the vibrational energy of the bonds
Molecules in the atmosphere collide
The kinetic energy of the molecules increases as energy is transferred between molecules
This raises the temperature of the atmosphere
Greenhouse gases emit some of the absorbed radiation
Some of this is also absorbed by the Earth increase concentration of greenhouse gases leads to enhanced greenhouse effect