H+ ions concentrations

The pH of a solution can be measured by an instrument called a pH meter. A pH meter translates the H+ ion concentration of a solution into an electrical signal that is converted into either a digital display or a deflection on a meter that reads pH directly (Figure 13.4). Later, in Chapter 18, we will consider the principle on which the pH meter works. 

In either case, the ratio nHBlnB- changes. This in turn changes the H+ ion concentration and pH of the buffer. The effect ordinarily is small, as illustrated in Example 14.4. 

Group II consists of six different cations, all of which form very insoluble sulfides (Figure A). These compounds are precipitated selectively by adding hydrogen sulfide, a toxic, foul-smelling gas. at a pH of 0.5. At this rather high H+ ion concentration. 0.3 M, the equilibrium... 

We will first consider acid-base balances, then redox systems. Finally, we will illustrate in conclusion that both the ultimate H ion concentration (pH) and electron concentration (p8) result from interactions of biogeochemical cycles. 

Solutions which resist changes in their pH values on the addition of small amounts of acids or bases are called buffer solutions or simply buffers. The resistance to a change in the H+ ion concentration on the addition of an acid or an alkali is known as buffer action. Just as the buffer of railway carriages resists shocks, similarly buffer solutions resist the action of various substances which can affect the pH value. There are two types of buffers (i) acidic buffer and (ii) basic buffer. 

The peripheral chemoreceptors include the carotid and aortic bodies. The carotid bodies, which are more important in humans, are located near the bifurcation of the common carotid arteries. The aortic bodies are located in the arch of the aorta. The peripheral chemoreceptors respond to a decrease in P02/ an increase in PC02, and a decrease in pH (increase in H+ ion concentration) of the arterial blood. 

The central chemoreceptors are located near the ventral surface of the medulla in close proximity to the respiratory center. These receptors are surrounded by the extracellular fluid (ECF) of the brain and respond to changes in H+ ion concentration. The composition of the ECF surrounding the central chemoreceptors is determined by the cerebrospinal fluid (CSF), local blood flow, and local metabolism. 

Table 17.2 Chemoreceptor Responses to Changes in Arterial P02, PC02, and H Ion Concentration...

Conversely, a decrease in the arterial PCOz due to hyperventilation results in a decrease in the H+ ion concentration in the ECF of the brain. Decreased stimulation of the central chemoreceptors (and therefore a decrease in the excitatory input to the medullary respiratory center) causes... 

Now, separating the ratio of H+ ion concentrations into two log terms we may have ... 

Plots of the activity of various enzymes as a function of pH give different curves, in some cases bell-shaped. The pH dependence of the activity could be the result of three fundamental effects of H ion concentration ... 

The toxicity due to local or absorptive action of solid arsenious oxide is considerably decreased by boric acid, probably because the solubility of the former, which is dependent on H+-ion concentration, is much less in the aqueous boric acid than in water with dissolved arsenious oxide the boric acid causes a retardation but no alleviation of the toxic action.4... 

Some of the volumetric methods described above may also be adapted to the electrometric determination of arsenic. Such methods have been described for titration of arsenites with ceric sulphate,9 iodine in the presence of sodium bicarbonate,10 chloramine (p-toluene-sulphone chloramide),11 alkaline potassium ferricyanide solution,12 potassium bromate13 or potassium iodate14 in the presence of hydrochloric acid, silver nitrate15 (by applying a secondary titration with 01N alkali to maintain the desired low H+-ion concentration), and with... 

Another source of nonmonotonic kinetics is the dependence of most biological reactions upon the H+ ion concentration (pH). This situation gives rise to nonmonotonic kinetics since the dependence of the enzyme rate of reaction upon pH is nonmonotonic (bell shaped) as shown in Figure 2.4. 

Autoxidation of DMS DMS is autoxidized by 02 very slowly in solution at ordinary temperatures but the reaction is catalyzed by metal ions. In a saline solution of pH 8, Brimblecombe and Shooter (University of East Anglia, unpublished data) obtained a first order rate constant of 2.2 x 10-8 s-1 at 20 C and an activation energy of 78 kJ. The rate was also found to decrease with pH (but not linearly dependent on the H+ ion concentration). In the presence of Cu(II) ions (10-4 M) at pH 5.6 and temperatures at 20° C, a tenfold increase in first order rate constant was observed (ka = 2 x 10-7 s-1). Reactions in NaG solutions were found to be nearly an order of magnitude slower than in seawater and at least an order of magnitude faster than in distilled water. 

Mitchell based his concept on the suggestion that as electron is transported along the respiratory chain, H+ ions are ejected to cytoplasm (the mitochondrion environment). As a consequence, a gradient of H+ ion concentration occurs in external and internal mitochondrial spaces. Of course, this H+ ion concentration gradient is supported by electron transfer free energy decrease and in the case of membrane impermeability for H+ ions. 

The respiration process produces electric potential difference on the membrane, and then H+ ion concentration gradient is formed on the membrane sides, which plays the important role in H+ ion transport. 

Isoelectric point is that point at which the concentration of the positive ions in solution becomes equal to that of the negative ions. Similarly, in case of colloidal solutions, a sol may be positively charged in presence of an acid, due to the preferential adsorption of H+ ions. On the contrary, a sol may be negatively charged in presence of an alkali, due to the preferential adsorption of OH ions. However, there must be an intermediate H+ ion concentration at which the colloidal particles are neither positively nor negatively charged. Hence, the isoelectric point in case of colloidal solution, is that point at which the colloidal solutions have no charge at all. 

Example An aqueous solution has an H+ ion concentration of 4.0X10 9 Is the solution acidic or basic What is the pH of the solution What is the pOH ... 

The assumed equilibrium between hypoastatous acid and its protonated form in aqueous solutions—influenced by the H+ -ion concentration—offered a possibility to study the electrophilic addition of astatine to the oleflnic bond of ethylene forming ethylene astato-hydrin(ll). 

Hydrogen ions occur everywhere in the body in small amounts as an ion but large amounts in water and aqueous liquids. They are also in aqueous solutions and body fluids. The correct balance of H+ in solution maintains the correct working pH values. pH is buffered frequently by proteins to maintain the best working values. Water is taken in as a liquid and also by eating plant material, etc. It is essential for maintaining H+ ion concentration... 

It will be realized that in the presence of a large H+ ion concentration (as distinct from the limited one due to the weak acetic acid), the Cr04 may be such that the solubility product of BaCr04 is not reached and under such conditions BaCr04 will not be precipitated this accounts for the solubility of this salt in dilute mineral acids. 

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