Bicarbonate ion HCO

We see that the existence of the stable bicarbonate ion, HCO foqj produces the chemical species, OH (aq) in common with solutions of the hydroxides. We can postulate that OH (ag) accounts for the slippery feel and bitter taste of the basic solutions. The stability of bicarbonate ion also explains the removal of acid properties through reaction (26). 

The most abundant anion delivered by rivers to the oceans is bicarbonate ion (HCO ), and most of the bicarbonate alkalinity in rivers comes from the weathering of carbonate rocks (Meybeck, 1987). The chemical weathering of limestones and dolostones by dissolved CO2 can be represented by the reactions for dissolution of calcite and dolomite ... 

Several factors must be taken into account. Firstly, there is the chemistry of seawater itself. Compared with distilled water or even a solution of sodium chloride (NaCl) of equivalent ionic strength (see Box 5.1) to the oceans, seawater has a significantly greater ability to take up excess C02. This comes about from the existence in seawater of alkalinity (see Sections 5.3.1, 6.4.4 Box 5.2) in the form of carbonate ions (COf ), which can react with C02 molecules to form bicarbonate ions (HCO ) ... 

However, the above theoretical amount of OH quantum yield can be reduced to about 0.5 because of the radical-radical recombination [Eq. (17)] and other scavenging compounds, such as H2O2 itself [Eq. (18)] and bicarbonate ions (HCOs ) [Eqs. (19-21)]... 

Another significant difference between definitions is that Brpnsted-Lowry acids andbases need not be molecular substances. There are a variety of reactions in which ions donate or accept protons. In the sample below, note how the cyanide ion (CN ) acts as a base by accepting a proton and the bicarbonate ion (HCO,) acts as an acid by donating a proton. 

Carbon dioxide reacts with water to form carbonic acid, H CX) i. ITiis reaction is accelerated by carbonic anhydnise, an enzyme abundant in red blood cells that will be considered extensively in Chapter 9. Carbonic acid is a strong acid with a pK, of 3.5. Thus, once formed, carbonic acid dissociates to form bicarbonate ion, HCO.Ct cind H, resulting in a drop in pH. This drop in pH stabilizes the T state by the mechanism discussed previously. 

Carbon dioxide is a major end product of aerobic metabolism. In mammals, this carbon dioxide is released into the blood and transported to the lungs for exhalation. While in the red blood cells, carbon dioxide reacts with water (Section 7.3). The product of this reaction is a moderately strong acid, carbonic acid (pfCa= 3.5), which is converted into bicarbonate ion (HCO ") on the loss of a proton. 

Limestone can form in two ways with or without the aid of living organisms. In the inorganic mechanisms, the chemical reactions that form calcium carbonate begin with the solution of atmospheric carbon dioxide (C02) in water. Dissolved C02 reacts with water to form carbonic acid (H2C03), the familiar acid in carbonated soda, which in turn reacts with water to form bicarbonate ions (HCO ). These reactions are represented by the following equations ... 

The pH of a bicarbonate-carbonic acid buffer is 8.00. Calculate the ratio of the concentration of carbonic acid (H2CO3) to that of the bicarbonate ion (HCO ). 

Carbonic anhydrases catalyze the reaction of water with carbon dioxide to generate carbonic acid. The catalysis can be extremely fast molecules of some carbonic anhydrases hydrate carbon dioxide at rates as high as 1 million times per second. A tightly bound zinc ion is a crucial component of the active sites of these enzymes. Each zinc ion binds a water molecule and promotes its deprotonation to generate a hydroxide ion at neutral pH. This hydroxide attacks carbon dioxide to form bicarbonate ion, HCOs. Because of the physiological roles of carbon dioxide and bicarbonate ions, speed is of the essence for this enzyme. To overcome limitations imposed by the rate of proton transfer from the zinc-bound water molecule, the most active carbonic anhydrases have evolved a proton shuttle to transfer protons to a buffer. 

Lake Acidification Lakes acidify when they lose alkalinity (Roth et al., 1985). The total alkalinity or acid-neutralizing capacity is the reservoir of bases in solution. The acidneutralizing capacity of a lake buffers it against large changes in pH. In natural clean waters, most of the acid-neutralizing capacity consists of bicarbonate ion, HCO. Carbonate alkalinity is defined by... 

Step 1 biotin is carboxylated using bicarbonate ion (HCO ") as the source of the carboxyl group. Step 2 the carboxylated biotin is brought into proximity with enzyme-bound acetyl-CoA by a biotin carrier protein. Step 3 the carboxyl group is transferred to acetyl-CoA, forming malonyl-CoA. 

Bicarbonate ions (HCOs") diffuse from the plasma into the red blood cells. 

Carbonic acid in aqueous solutions dissociates to form the bicarbonate ion (hCO and a hydrogen ion (H+). 

Calcium and magnesium occur as bicarbonates primarily. Lime and caustic soda break down the bicarbonate ions (HCOs) into water molecules and insoluble carbonate ions (COs) as follows ... 

Recall from the "Chemistiy and Life" box in Section 2.7 that zinc is needed in our diets in trace amounts. Zinc is an essential part of several enzymes, the proteins that facilitate or regulate the speeds of key biological reactions. For example, one of the most important zinc-containing enzymes is carbonic anhydrase. This enzyme is found in red blood cells. Its job is to facilitate the reaction of carbon dioxide (CO2) with water to form the bicarbonate ion (HCOs ) ... 

About 25% of the total CO2 in the body is carried from body tissues to the lungs in the form of carbaminohemoglobin. Another 5% dissolves in the plasma and travels in solution the remaining 70% is transported in the form of bicarbonate ions (HCOs ). 

A buffer system prevents marked changes in the pH of a solution when an acid or base is added. Three major buffer systems of the blood are the bicarbonate buffer, the phosphate buffer, and the plasma proteins. The most important of these is the bicarbonate buffer system, consisting of a mixture of bicarbonate ions (HCOs ) and carbonic acid (H2CO3). 

The formula for the compound is written by enclosing the formula of the bicarbonate ion, HCOs , in parentheses and writing the subscript 3 outside the right parenthesis. 

Carbon dioxide (CO ) is slightly soluble in water (as shown below), giving the familiar carbonic acid (H COj) found in soft drinks. In aquatic systems, H COj dissociates into bicarbonate ions (HCO 3) and carbonate ions (CO 3 ), as shown by the following equations ... 

The simplest way to relieve mild heartburn is to swallow repeatedly. Saliva contains the bicarbonate ion (HCOs ), which acts as a base and, when swallowed, neutralizes some of the acid in the esophagus. Later in this chapter, we will see how bicarbonate acts as a base. You can also treat heartburn with antacids such as Turns, milk of magnesia, or Mylanta. These over-the-counter medications contain more base than saliva and therefore are effective at neutralizing esophageal acid. We look at the bases in these medicines more carefully later (see the Chemistry and Medicine box in Section 15.7). 

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