Module 5 Section 1

Question 1

acids and bases

Answer 1

• refers to the regulation of hydrogen ions (H+) in the body fluids
• acids are defined as substances which release H+ when in solution
• bases are substances which bind with free H+ in solution

Question 2

acids

Answer 2

• defined as hydrogen-containing substances, that when in a solution, dissociate into H+ and an anion
• although many substances contain hydrogen, they are not necessarily classified as acids if their hydrogen is very tightly bound such that it does not separate from the molecule

Question 3

examples of acids

Answer 3

example 1 - hydrochloric acid (HCl)
- in solution, dissociates almost entirely into H+ and Cl-

example 2 - carbonic acid H2CO3
- dissociates into H+ and HCO3-
- when you put H2CO3 in a solution such as water, within the water you will find H2CO3, but also find H+ and HCO3- since the H+ dissociated from the H2CO3 to form HCO3-
- the degree to which the H+ dissociate defines wheather or not a substance is a strong acid or a weak acid

Question 4

strong acids vs. weak acids

Answer 4

• the more H+ that dissociates, the stronger the acid
• HCl is a strong acid while H2CO3 is a weak acid
• if you were to put the same number of molecules of each into a solution, the number of H+ dissociated from HCl would be greater than those dissociated from H2CO3

Question 5

strong acid

Answer 5

a strong acid, such as hydrochloric acid (HCl), completely dissociates into free H+ and anions in solution

Question 6

bases

Answer 6

• bases are simply substances that will bind free H+ and remove it from solution
• like acids, there are strong and weak bases
• the stronger the base, the easier it can bind H+

Question 6

weak acid

Answer 6

a weak acid, such as carbonic acid (H2CO3), only partially dissociates into free H+ and anions in solution

Question 7

steps of base dissociation

Answer 7

1. a flask is filled with distilled water
2. a strong base, NaOH, is added t the water filled flask
3. the NaOH will dissociate to Na+ and OH-. this decreases the concentration of free H+ as the OH- binds to any free H+ to form water

Question 8

pH designation

Answer 8

• pH was developed to express the amount of H+ is a solution in a more convenient manner
• the concentration of H+ or [H+] in the ECF is usually 4x10^-8 moles/L or M which is a really low concentration
• even small changes in [H+] that we might expect to be negligible, can have a big effect

Question 9

pH formula

Answer 9

1. because H+ is the denominator in the equation, the higher the [H+], the lower the pH. the lower the pH, the more acidic the solution. basic solutions have higher pH since the [H+] is lower
2. each pH unit represents a 10-fold change in [H+] since it is a logarithmic scale. a solution with a pH of 7.0 has 10 times less [H+] than a solution with a pH of 6.0

Question 10

pH values

Answer 10

• pure water has a pH of 7.0 which is what we consider a “neutral” pH
• it is called neutral because very little of the water has dissociated into H+ and OH-, so it is neither acidic nor basic
• solutions with a pH less than 7.0 have more free [H+] than water so they are considered acidic
• solutions with a pH greater than 7.0 have less free [H+] than water so they are considered basic or alkaline

Question 11

substances at certain pH levels

Answer 11

• pH 2: lemon
• pH 2.4: vinegar
• pH 4.7: bananas
• pH 6.6: milk
• pH 8.9: sodium bicarbonate
• pH 10: soaps (giving slippery character)
• pH 14: drain cleaner

Question 12

acidosis and alkalosis in the body

Answer 12

• normal pH of arterial blood is 7.45 and the normal pH of venous blood is 7.35
• we typically take the average of these two values 7.4 when discussing the normal blood pH
• acidosis exists whenever blood pH falls below 7.35 and alkalosis occurs when blood pH rises above 7.45
• sever changes in pH are not compatible with life
• a pH less than 6.8 or greater than 8.0 will result in death within a few seconds

Question 13

main effects of large changes in pH - effect 1

Answer 13

• the function of nerve and muscle cells are affected
• acidosis causes suppression of the central nervous system
• early symptoms include disorientation but can rapidly lead to coma and death
• alkalosis leads to over-excitability of both the central and peripheral nervous system
• extreme alkalosis can cause death by spasms of the respiratory muscles or from convulsions

Question 14

main effects of large changes in pH - effect 2

Answer 14

• the acitvity of most enzymes in the body are optimized for a pH of 7.4
• when pH changes, it can either speed up or slow down enzymatic reactions
• in either case, the consequences can be deleterious

Question 15

main effects of large changes in pH - effect 3

Answer 15

• changes in [H+] can lead to changes in the amount of K+ in body fluids
• H+ can substitute for K+ in secretion
• if the blood is acidotic, then more H+ than K+ will be secreted, resulting in an increase in plasma K+
• this has a serious consequence on excitable cells, as increasing K+ can cause them to depolarize and become more excitable

Question 16

where is H+ produced in the body

Answer 16

• under normal conditions there is an almost constant production or release of H+ into the body fluids
• the majority of it comes from metabolic acitivities
• there are 3 primary sources

Question 17

first primary source of H+ production

Answer 17

carbonic acid formation
- the metabolic by-products of cellular respiration are CO2 and H2O
- in the presence of carbonic anhydrase, CO2 and H2O are converted into carbonic acid (H2CO3), which then dissociates into bicarbonate (HCO3-) and H+ by the equation shown
- as long as respiration balances metabolic acitivity, there is no net increase or decrease in H+

Question 18

second primary source of H+ production

Answer 18

inorganic acids produced from breakdown of nutrients
- dietary proteins contain a lot of sulphur and phosphorus whcih, when broken down, form sulphuric acid and phosphoric acid, both of which are strong acids and freely dissociate
- other foods such as vegetables and fruits tend to produce more bases than acids so they help to counter the H+ formed from protein metabolism
- in protein rich diets, an excess of H+ is produced

Question 19

third primary source of H+ production

Answer 19

organic acids from intermediary metabolism
- examples of these are fatty acids produced during fat metabolism and lactic acid produced in msucles
- although they are weak acids, they still dissociate to contribute to the free pool of H+