The Significance of pH🧪

Question 1

Where are Buffers important?

Answer 1

In living systems

Question 2

State 2 functions of buffers in the body?

Answer 2

-Maintain pH of the body within normal pH ranges
-Ensure enzymes and other cellular processes function optimally

Question 3

What are the normal pH values of the following substances in the body?

Blood?
Urine?
Gastric Fluid?
Saliva?

Answer 3

Blood- 7.4
Urine- 6.0 (range 4.4-8.0)
Gastric Fluid- 2.0
Saliva- 6.2- 7.2

Question 4

Name the two major inorganic buffers in the body and their function

Answer 4

Phosphate- Buffer Reserve in Skeleton
Bicarbonate- Major Buffer in Human Body

Question 5

Name an organic buffer in the body

Answer 5

Macromolecules i.e. amino acid side chais in proteins- can also act as buffers

Question 6

Name an organic buffer in the body

Answer 6

Macromolecules i.e. amino acid side chais in proteins- can also act as buffers

Question 7

Many molecules in biological Systems are what?
And what are their ionic properties Influenced by?

Answer 7

Many molecules in biological systems are weak acids and/or weak bases

Their ionic properties are influenced by their hydrogen ion concentration [H+]

Question 8

How would you calculate the pH of a STRONG ACID?

Answer 8

pH= -log[H+]

Question 9

What happens when acids dissociate?

Answer 9

They release [H+] ions

Question 10

What is an acid?

Answer 10

A substance that will dissociate in water to produce [H+] ions

-PROTON DONATOR

Question 11

What is a base?

Answer 11

A substance which in water tends to combine with [H+] ions

-PROTON ACCEPTOR

Question 12

Write an equation to demonstrate the dissociation of acids

Answer 12

A <——–> H+ + B-
acid conjugate base

In water;

HA + H20 ———> H30+ + A-
acid water con. acid con.base

Question 13

A ———> H+ + B-

This equilibrium reaction always involves what?

Answer 13

A conjugate acid-base pair, comprising a hydrogen ion (acid) donor and an acceptor (base)

Question 14

For the dissociation constant of an acid, how is the forward reaction balanced?

Answer 14

By the reverse reaction

Question 15

A <——–> H+ + B-
Describe the concentrations of A, H+ and B- when an equilibrium is established?

Answer 15

The ratio of the concentrations of H+ and B- to A is constant when an equilibrium is established

Question 16

What equation is used to calculate the acid dissociation constant?

Answer 16

For A <——–> H+ + B-

Ka= [H+][B-]
————
[A]

Question 17

A <——–> H+ + B-

Describe what happens to the value of K as the strength of the acid increases

Answer 17

As the strength of the acid increases, the higher the degree of dissociation so the value of K increases as the reaction is pushed to the right, producing more conjugate base

Question 18

What is the Henderson- Hasselbalch Equation?

Answer 18

Question 19

How would you calculate pKa if given the value of Ka

Answer 19

pKa = -logKa

Question 20

Describe the relationship between acid strength and Ka

Answer 20

Directly Proportional
-As the strength of the acid increases so does the value of Ka
-The larger the value of Ka the smaller the pH

Question 21

Describe the relationship between acid strength and pKa

Answer 21

-Inversely Proportional
-As the strength of the acid increases the value of pKa decreases
-The larger the value of pKa the higher the pH

Question 22

What are indicators?

Answer 22

Weak acids or bases which have a distinct colour difference between their ionised form (In-) and their unionised form (HIn).

e.g. HIn- colourless
In- - red

Question 23

The degree of dissociation and pH of indicators are related by what equation?

Answer 23

pH= pKa + log [In-]
——
[HIn]

Question 24

Why is very little indicator added to solutions?

Answer 24

So that the pH of the solution is unaffected

Question 25

How is the ratio of [In-]/[HIn] determined?

Answer 25

By the pH

Question 26

What determines the colour of the indicator?

Answer 26

The ratio of [In-]/[HIn]

Question 27

How can you measure the pH of a solution based on the colour of the indicator solution?

Answer 27

When either the ionised, or unionised form of the indicator is coloured, the depth of colour for the given amount of indicator can be used to measure pH

Question 28

What is an electrical method of measuring pH?

Answer 28

-pH meter

Question 29

Describe what a pH meter is

Answer 29

-Measurement made using a glass electrode
-Glass electrode- thin walled glass bulb containing a platinum electrode immersed in 1M Hal

Question 30

What do buffer solutions do?

Answer 30

Resist changes in pH when acid or base is added

Question 31

What do buffer solutions consist of?

Answer 31

A conjugate acid-base pair of either a weak acid or weak base

Question 32

Buffering systems in the body play a vital role in what?

Answer 32

Maintaining pH homeostasis

Question 33

What does buffering in the oral cavity limit?

Answer 33

pH changes caused by acid production by plaque bacteria

Question 34

Using the Henderson Hasselbalch Equation;

pH = pKa- log [Acid]
——–
[Base]
When is optimum buffering capacity?

Answer 34

-It can be shown that buffering is most effective when [Acid]= [Base]

• [A]=[B] so log(1)=0 hence pH=pKa

-Buffers operate optimally at their pKa ie when HALF DISSOCIATED (as [A]=[B])

-At optimum buffering capacity pH=pKa

Question 35

Describe how plaque bacteria results in dental caries

Answer 35

-Plaque Bacteria ferment dietary carbohydrates to produce acid
-This causes plaque pH to fall
-Leading to increased solubility of Dental Enamel
-Which if not reversed leads to Dental Caries

Question 36

Describe how Saliva prevents Dental Caries

Answer 36

-Saliva acts as a buffer and neutralises the acid produced by plaque bacteria and thereby prevents dental caries (if buffering is adequate)

Question 37

Where is bicarbonate an important buffer?

Answer 37

Extremely important buffer in body fluids such as blood

Question 38

What proteins does saliva contain?

Answer 38

Unusual Proteins that are histadine rich and are known as histatins; these too are important buffers in saliva

Question 39

What is Histadine?

Answer 39

An amino acid which is very good at acting as a buffer