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Name: Tom
Status: student
Grade: 12+
Location: Outside U.S.
Country: Spain
Date: Winter 2013-14


Question: Last week, my teacher asked me to guess whether human blood's acidic or basic. At first, I had two different ideas: 1. It's acidic because there's carbonic acid 2. It's basic because there's sodium hydrogencarbonate Then, I looked it up on Wikipedia(although I knew it's sometimes unauthoritative), and I found that human blood's slightly basic. On the following day, I asked a teaching assistant, a biology teacher and a chemistry teacher. They all said that it's acidic because of carbonic acid. However, I trusted Wiki more and I believed that human blood's basic. But how should I explain it to my teachers?? Also, my teachers didn't allow us to use "bicarbonate" and "basic", we must use "hydrogencarbonate" and "alkaline". Is there any different actually?



Replies:
The blood is definitely slightly basic. The pH of your blood must stay between 7.35 and 7.45. If it strays much in either direction you will definitely feel symptoms. The reason you have bicarbonate and carbonic acid in your blood is because they are really versions of each other. Yes, carbon dioxide and water combine to make carbonic acid, and most of the CO2 in your body travels through your blood.

CO_2 + H_2O => H_2CO_3 =>HCO_3^- + H+

(From Wikipedia-http://en.wikipedia.org/wiki/Bicarbonate_buffering_system)

But carbonic acid can ionize into bicarbonate and hydrogen ion. If there is a lot of acid in the blood, bicarbonate can combine with it to create carbonic acid which is a weak acid. If there is a lot of base, hydrogen ion can combine with it to form carbonic acid making the blood less basic. You also have the kidneys which can remove acid- your urine is usually slightly acidic because of this. Also, your lungs are breathing out CO2 all the time, also getting rid of acid. You have receptors in your brain that monitor the CO2 level in your blood and if it is too acid, you will start breathing faster to compensate. So, your body has many ways of keeping the blood's pH in a very narrow range, which is slightly basic.

vanhoeck



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