pH Scale - Online Tutor, Practice Problems & Exam Prep

The pH scale, ranging from 0 to 14, measures hydrogen ion concentration, crucial for biological processes. A pH below 7 indicates acidity, while above 7 indicates basicity; a pH of 7 is neutral. Buffers, like the bicarbonate buffer system, help maintain pH around 7, resisting changes from added acids or bases. This homeostasis is vital for living organisms, as even slight pH shifts can be harmful. Understanding these concepts is essential for grasping the biochemical balance necessary for life.

pH Scale

In this video, we're going to begin our lesson on pH and the pH scale. It's important to recall from some of our previous lesson videos that the concentration of hydrogen ions is incredibly important when it comes to life. Many biological processes in living organisms are strongly affected by the concentration of dissolved hydrogen ions. If the concentration of dissolved hydrogen ions is not in the correct range, then the biological processes may not work because they are strongly affected by the concentration of hydrogen ions. It's in the scientists' best interest to be able to measure the concentration of hydrogen ions because it has such a strong effect on biological processes. This is exactly where the pH comes into play because pH is really just a logarithmic measurement of the hydrogen ion concentration in a solution. By using the pH, scientists can determine the amount of hydrogen ions in a solution, and once again, the concentration of hydrogen ions strongly affects biological processes. It's important for scientists to be able to measure hydrogen ion concentration using pH.

It's also important to keep in mind that pH is not only a direct measurement of hydrogen ion concentration but is also able to indirectly measure the hydroxide ion concentration, or the OH^- ion concentration in aqueous solutions where the solvent will be water. The pH scale is a scale that goes from 0 at its minimum to 14 at its highest and can be used to determine if a solution is going to be acidic or basic. Each section of this scale represents a different type of solution: acidic, basic, or neutral.

A pH of 7 is right in the middle of 0 and 14. When the pH is lower than 7, this indicates an acidic solution with very low pHs. Conversely, with very high pHs above 7, the solution is basic. Neutral solutions have a pH exactly equal to 7. Another important detail to remember is that the value of the pH is inversely proportional to the hydrogen ion concentration. When the pH is low, the hydrogen ion concentration is high, and when the pH is high, the hydrogen ion concentration is low. This relationship is exemplified through the distribution of acidic, basic, and neutral solutions across the pH scale.

Noticeable examples on the pH scale indicate that battery acid has a very low pH, lemon juice has a pH of around 2, tomato juice is around 4.2, black coffee has a pH of 5, and milk is slightly acidic. Pure water has a neutral pH of 7, while ocean water is slightly basic with a pH of about 8, similar to baking soda. Ammonia has a pH of about 12, and bleach has a pH between 12 and 13, while drain cleaner has a pH of about 14.

This introduction to pH and the pH scale provides a foundation for understanding the crucial role of hydrogen ion concentration in biological processes and how scientists measure and interpret these values through the use of the pH scale. We'll be able to get some practice applying these concepts as we move forward, so I'll see you all in our next video.

In a neutral solution, the concentration of __________.

a) Hydrogen ions is less than the concentration of hydroxide ions.

b) Water molecules is less than the concentration of hydroxide ions.

c) Hydrogen ions is greater than the concentration of hydroxide ions.

d) Hydrogen ions is equal to the concentration of hydroxide ions.

• A. Hydrogen ions is less than the concentration of hydroxide ions.
• B. Water molecules is less than the concentration of hydroxide ions.
• C. Hydrogen ions is greater than the concentration of hydroxide ions.
• D. Hydrogen ions is equal to the concentration of hydroxide ions.

A base _______:

a) Has a value of 7 on the pH scale.

b) Is a chemical that donates hydrogen ions to a solution.

c) Is a chemical that accepts hydrogen ions from a solution.

d) Has a value below 7 on the pH scale.

e) None of the above are correct.

• A. Has a value of 7 on the pH scale.
• B. Is a chemical that donates hydrogen ions to a solution.
• C. Is a chemical that accepts hydrogen ions from a solution.
• D. Has a value below 7 on the pH scale.
• E. None of the above are correct.

Buffers

In this video, we're going to begin our introduction to buffers. First, we need to note that the pH of most living organisms is actually maintained right around a value of 7 or having a neutral pH. Changing the pH even slightly can be really harmful to living organisms. It's in the best interest of living organisms to make sure that the pH stays around 7, in its neutral range. In order to ensure that the pH stays around 7, living organisms use what are known as buffers. Buffers are defined as substances that are capable of resisting changes in the pH even when acids and bases are added to the solution. Typically, acids and bases would change the pH. However, if buffers are present in the solution, then even when acids and bases are added, the substance is capable of resisting changes in pH, which means that the pH will not change. This is beneficial for living organisms because if the pH changes too much, it can be really harmful. These buffers are beneficial for cells to ensure that the pH resists changes and stays in the neutral range.

Depending on the situation, buffers are capable of either decreasing or increasing the concentration of hydrogen ions in the solution. Living organisms use buffers to help maintain the pH or help maintain homeostasis regarding the pH values. If we look at our image on the left-hand side, we see a pH scale, which we know ranges from 0 up to 14. Values of 0 are acidic, and values of 14 are basic, while a value of 7 is neutral. Most living organisms require a pH of about 7 to survive. If the pH were to tip to either side, too much acid or base could be really harmful. It's in the cell's best interest to ensure that the pH is maintained and able to resist changes, staying about the same.

Here, we're showing an example of the bicarbonate buffer system, which is found in our blood and helps to maintain the pH of our blood. On the right-hand side, we focus on the bicarbonate buffer system, which includes these two molecules that we see here, HCO3− and HHCO3. Notice that on the left-hand side, we are showing hydrogen ions, and remember that the pH reflects the number of hydrogen ions. If there are many hydrogen ions, then we would have an acidic solution. However, if there are not many free hydrogen ions, as shown here where there's no H+ anywhere, that means the pH is high and it's going to be a basic solution.

Here, it is noted that HCO3− is part of a buffer system because it is capable of accepting hydrogen ions if the hydrogen ion concentration gets too high. In such a scenario, bicarbonate can act to lower the hydrogen ion concentration by accepting hydrogen ions. This action causes the reaction to move towards the right, which will increase the pH. The pH is increased when HCO3− accepts hydrogen ions. However, if the hydrogen ion concentration were to get too low, HHCO3 is capable of donating hydrogen ions. Depending on the situation, buffers, which include HCO3− here and HHCO3, are capable of either decreasing or increasing the hydrogen ions in the solution. This helps maintain homeostasis in regards to the pH. This concludes our introduction to buffers and we will be able to get some practice applying these concepts moving forward in our course. I'll see you all in our next video.

Which of the following statements about buffers is true?

a) They maintain a consistent pH only when acids are added to them, but not bases.

b) They maintain a consistent pH of 7.

c) They fluctuate in pH when acids are added to them.

d) They maintain a consistent pH when acids or bases are added to them.

e) They fluctuate in pH when acids or bases are added to them.

• A. They maintain a consistent pH only when acids are added to them, but not bases.
• B. They maintain a consistent pH of 7.
• C. They fluctuate in pH when acids are added to them.
• D. They maintain a consistent pH when acids or bases are added to them.
• E. They fluctuate in pH when acids or bases are added to them.

Here’s what students ask on this topic:

What is the pH scale and how does it work?

The pH scale is a logarithmic scale ranging from 0 to 14 that measures the concentration of hydrogen ions (H⁺) in a solution. A pH of 7 is considered neutral, meaning the concentration of H⁺ ions is equal to the concentration of hydroxide ions (OH^-). A pH below 7 indicates an acidic solution, where the concentration of H⁺ ions is higher than that of OH^- ions. Conversely, a pH above 7 indicates a basic (alkaline) solution, where the concentration of OH^- ions is higher than that of H⁺ ions. The pH scale is crucial for understanding the chemical environment in biological systems, as many biological processes are sensitive to changes in pH.

Why is pH important in biological systems?

pH is crucial in biological systems because it affects the structure and function of molecules, enzyme activity, and overall cellular processes. Many enzymes, which are proteins that catalyze biochemical reactions, have an optimal pH range in which they function most efficiently. Deviations from this optimal pH can lead to denaturation of enzymes and other proteins, disrupting metabolic processes. Additionally, pH affects the solubility and availability of nutrients and ions, impacting cellular homeostasis and function. Therefore, maintaining a stable pH is vital for the proper functioning of biological systems.

What are buffers and how do they help maintain pH in biological systems?

Buffers are substances that resist changes in pH when acids or bases are added to a solution. They work by either absorbing excess hydrogen ions (H⁺) or donating hydrogen ions when the concentration is too low. This helps maintain a stable pH, which is crucial for biological systems. For example, the bicarbonate buffer system in human blood helps maintain a pH around 7.4. This system involves bicarbonate ions (HCO₃^-) and carbonic acid (H₂CO₃), which can neutralize excess acids or bases, thereby stabilizing the pH and ensuring proper physiological function.

How does the concentration of hydrogen ions relate to pH?

The concentration of hydrogen ions (H⁺) is inversely proportional to the pH of a solution. This means that as the concentration of H⁺ ions increases, the pH decreases, making the solution more acidic. Conversely, as the concentration of H⁺ ions decreases, the pH increases, making the solution more basic. Mathematically, pH is defined as the negative logarithm of the hydrogen ion concentration: $\mathrm{pH}=-{\log }_{10}\left(\mathrm{[H⁺]}\right)$. This relationship is crucial for understanding how changes in H⁺ concentration affect the acidity or basicity of a solution.

What is the role of the bicarbonate buffer system in blood pH regulation?

The bicarbonate buffer system is essential for maintaining the pH of human blood around 7.4. It involves bicarbonate ions (HCO₃^-) and carbonic acid (H₂CO₃). When the blood becomes too acidic, bicarbonate ions can neutralize excess hydrogen ions (H⁺), forming carbonic acid, which then dissociates into water and carbon dioxide, which is exhaled. Conversely, if the blood becomes too basic, carbonic acid can dissociate to release hydrogen ions, lowering the pH. This dynamic equilibrium helps maintain a stable pH, crucial for proper physiological function.