Notes
Introduction to Acids and Bases
Sections
Key Principles of Acids and Bases:
Acids and bases are defined by their ability to donate or accept hydrogen ions
Acids are chemical substances that can donate/release, hydrogen ions in water.
Bases, aka, alkalines, are chemical substances that can accept hydrogen ions.
pH
pH is a measure of the concentration of hydrogen ions in solution
pH scale displays the concentration of hydrogen ions from 0 – 14.
An acidic solution has a pH less than 7; it has a high concentration of hydrogen ions.
A neutral solution has a pH of 7.
A basic solution has a pH of greater than 7; it has a lower concentration of hydrogen ions.
Calculation of pH: Negative logarithmic function.
pH values for human bodily fluids:
Gastric juice, which is secreted by organs of the digestive system, has a pH value around 2; its acidity aids in food digestion.
Saliva is slightly acidic, but much closer to neutral than are the gastric juices.
For comparison, pure water has a neutral pH, 7.
Arterial blood has a pH of approximately 7.4
Homeostasis & Buffers
Biological organisms are constantly adding acids to their bodily fluids during metabolism, but our blood is slightly basic.
Intra- and extra-cellular buffers operate to maintain homeostasis.
Buffers minimize changes of pH in solutions; they reversibly donate or accept hydrogen ions.
Example: Bicarbonate buffer system:
When hydrogen ions are added to the extracellular fluid, they combine with bicarbonate to produce carbonic acid, which is a weaker acid.
If the extracellular fluid becomes too basic, the reaction can be reversed:
Carbonic acid can dissociate to form hydrogen ions and bicarbonate; when pH increases (becomes more alkaline), carbonic acid dissociates to form bicarbonate, which is a base, and hydrogen ions.
Clinical Consequences
If the body cannot maintain homeostasis due to pathology, disturbances in bodily fluid pH inhibit enzymatic reactions.
Thus, failure to regulate pH causes a range of clinical symptoms associated with acidosis (too high blood acid content) or alkalosis (too low blood acid content); elsewhere, we discuss how the kidneys and lungs work to maintain homeostatic pH levels.
Full-Length Text
- Here we will learn an overview of acids and bases.
- To begin, start a table; Denote and show that:
- Acids and bases are defined by their ability to donate or accept hydrogen ions.
- Acids are chemical substances that can donate, or release, hydrogen ions in water;
- Bases, aka, alkalines, are chemical substances that can accept hydrogen ions;
- Be aware that acids and bases have additional unique characteristics that we will omit, for simplicity.
- Denote that the pH scale displays the concentration of hydrogen ions from 0 – 14, along a continuum, so that:
- An acidic solution has a pH less than 7;
- A neutral solution has a pH of 7;
- A basic solution has a pH of greater than 7.
- To calculate pH, scientists use a negative logarithmic function.
Now, let's illustrate the meaning of pH and learn how to read the pH scale.
- Write that pH is a measure of the concentration of hydrogen ions in solution.
- Draw an arrow and indicate high concentration of hydrogen ions on one end, and a low concentration of hydrogen ions on the other.
- Show that an acidic solution has LOW pH because it has a higher concentration of hydrogen ions, shown in pink.
- A solution with a HIGH pH has a lower concentration of hydrogen ions relative to hydroxide ions, which are bases, shown in blue.
- Show that a neutral solution has an equal number of hydrogen and hydroxide ions.
- Be aware that this arrow does not reflect the true mathematical relationship between hydrogen ion concentration and pH, which is logarithmic; our arrow is simply used to show directionality.
Next, let's illustrate these concepts on the pH scale;
- Show that solutions with pH values less than 7 are relatively acidic;
- Solutions with values greater than 7 are relatively basic, and, again,
- Solutions with a value of 7 are neutral.
- Notice that acidic solutions have high concentrations of hydrogen ions, but low pH values, and vice versa for basic solutions.
- Though this might seem counter-intuitive, the low pH value associated with acidic solutions is due to the negative sign in front of the formula used to calculate pH.
Next, let's indicate the approximate values of some key biological fluids in humans.
- First, show that gastric juice, which is secreted by organs of the digestive system, has a pH value around 2; its acidity aids in food digestion.
- Show that saliva is slightly acidic, but much closer to neutral than are the gastric juices.
- Show that pure water has a neutral pH, 7;
- And, arterial blood has a pH of approximately 7.4.
Next, consider the fact that biological organisms are constantly adding acids to their bodily fluids during metabolism, but our blood is slightly basic. This is because intra- and extra-cellular buffers operate to maintain homeostasis.
- Write that buffers minimize changes of pH in solutions;
- They reversibly donate or accept hydrogen ions.
- For example, consider the bicarbonate buffer system:
- When hydrogen ions are added to the extracellular fluid, they combine with bicarbonate to produce carbonic acid, which is a weaker acid.
- Or, if the extracellular fluid becomes too basic, the reaction can be reversed:
- Carbonic acid can dissociate to form hydrogen ions and bicarbonate.
- When pH increases (becomes more alkaline), carbonic acid dissociates to form bicarbonate, which is a base, and hydrogen ions.
- When pH decreases (becomes more acidic), the equation is reversed: bicarbonate and hydrogen ions combine to form carbonic acid.
However, if the body cannot maintain homeostasis due to pathology, disturbances in bodily fluid pH have clinical consequences:
- The enzymes that facilitate chemical reactions in our bodies are only active within specific blood pH ranges; outside of those ranges, the chemical reactions are inhibited.
- Thus, failure to regulate pH causes a range of clinical symptoms associated with acidosis (too high blood acid content) or alkalosis (too low blood acid content); elsewhere, we discuss how the kidneys and lungs work to maintain homeostatic pH levels.