pH

H+ and OH-

I lied.  Water or H₂O actually exists as H⁺ cations and OH^– anions.  It’s as if Mickey Mouse here did a Van Gogh move and chopped its ear off.  The ear, or the hydrogen leaves with its proton, but not with its electron.  Remember that hydrogen’s electron is attracted to anything else but its corresponding proton.  The OH part leaves with all the electronsNegatively charged subatomic particles found in atoms., making it an anionA negatively charged ion. because it has one extra electron. 

H⁺ cations will be incredibly significant to use in this class because these are what the pH scale measures.  pH is not a measurement of acidity, but a measurement of the ration of H⁺ cations to OH^– anions.  When they are in the proportion of twice as many hydrogen cations(H⁺): Protons that influence pH levels in body fluids. as OH^– anions then we have waterThe universal solvent essential for life..  The problem is that your body make H⁺ cations all day long.  No, it does not make the corresponding OH^– anions, just the H⁺ cations.  This tips that balance or proportion of H⁺ to OH^– making the cations outweigh the anions.  Since pH is a measurement of that proportion, the pH changes also. 

pH

This is the pH scale.  I want to point out that this is a man-made scale.  We needed some way to quantify pH and this scale is it.  The pH scale ranges from 0 to 14.  The numbers indicate something about the proportion of H⁺ cations to OH^– anions.  In the pictures on the right, you can see that proportion of H⁺ cations and OH^– anions.  Let’s start at the mid-point of the pH scale, which is a pH of 7, or neutralA solution with a pH of 7. pH.  This means that the numbers of H⁺ cations is equal to the number of OH^– anions.  No, 7 does not mean that there are 7 cations and 7 anions.  In factA statement based on direct observation that is repeatedly confirmed. the 7 is the result of a logarithmic equation that we will not concern ourselves with here.  Water is neutral.  Blood is slightly higher than neutral and comes in at about 7.35 to 7.45. 

Let’s move on to acidicA solution with a pH below 7, having a higher concentration of H⁺ ions. substances.  These are substances that have a value lower than 7 on the pH scale.  These substances have an excess of H⁺ cations compared to the OH^– anions.  These include things such as orange juice and coffee. They also include other non-consumables such as battery acidA substance that releases hydrogen ions (H⁺) in solution., which has a pH close to that of your stomach.  Oh, and heartburn is over-acidity of your stomach contents.  As well as the burping up of those contents, but that’s for another lecture.  I once had a student ask me what was the pH of the most acidic things on Earth.  “0!” I proclaimed.  But, then he asked what would happen if we discovered something more acidic than that.  We’d rearrange the logarithmic equation so that the new substance was 0.  He replied that was cheating.  Yes, but that’s science – we have to adjust for new discoveries.  You are producing H⁺ cations throughout the day. Consequently, your blood is becoming acidic. This happens without making the corresponding OH^– anions throughout the course of the day.  Your negative feedbackA control mechanism that reverses a change in the body to maintain homeostasis. mechanisms are reversing that change to keep your blood in the correct pH range.  Complicating this is also the fact that carbon dioxide is acidic and you are making that all day long too.  Your life is basically a big battle to keep from being acidic.  Don’t worry, it’s not just humans that do this, it’s all living things.

We have a feel for acidity. We understand its values on the pH scale. We know the proportion of H⁺ cations to OH^– anions. You are drawn to that part of the pH scale.  The values of 7 to 14 on the pH scale reflect alkalinity or basicA solution with a pH above 7, having a lower concentration of H⁺ ions. substances.  Tums.  Rolaids.  What other heartburn meds can you think of?  Oh, blue cheese to pair with those hot, spicy, and acidic wings.  Powerful cleaners such as bleach and ammonia also fall at this range of the scale.  We don’t deal with alkalinity in the human body nearly as much as we deal with acidity. 

Buffers

Thankfully, there are substances in your blood that are called buffersSubstances that resist changes in pH..  Buffers resist a change in pH by absorbing the excess H⁺ cations or the excess OH^– anions.  If your blood is acidic, there are substances that can bond with the excess H⁺ cations, raising your blood’s pH.  These are buffers that not only help to resist change. They also help to bring it back into the correct range.  Many proteinsLarge molecules made of amino acids with various functions in the body. act as buffers against acidity in your blood. This is beneficial because you tend to go acidic during the day.  You have buffers that also resist an increasing pH change, but not nearly as many.

The bicarbonate(HCO₃⁻) – A crucial buffer in blood that helps maintain pH balance; formed when carbon dioxide anion is one that is important to know in this class.  This is HCO₃^– and it is made using the carbon dioxide that your cellsThe basic structural and functional units of life. make in cellular respirationThe process of gas exchange, including ventilation, external and internal respiration..  You might also know of sodium(Na⁺): Major ECF cation; important for fluid balance, nerve function. bicarbonate which is baking soda.  Bicarbonate is a blood buffer and has an almost limitless supply since you make it all day long.  This is good. You are making those acidic H+ cations all day long. The alkaline bicarb anion bonds with them. It removes their effect on your pH.

What happens if all the buffers in your blood are occupied, but you are still acidic?  Your lungs and your kidneys also play a part in managing your pH.  But, they don’t like to do anything unless the blood buffers are all exhausted.  Remember I said that carbon dioxide is acidic?  Well, if your blood is too acidic, your breathing rate will increase. It tries to blow off the carbon dioxide you are making. This process raises your pH.  If your blood is too basic, your respiratory rate will decrease. Your body tries to hold in the acidic carbon dioxide to lower your pH.  If the lungs aren’t able to make the desired change, the kidney reluctantly steps in. It manages those H⁺ for you.