Occupied proton level

A Chart of Occupied and Vacant Proton Levels. With two exceptions, each of the values of J given in Tables 9, 10, and 11 refers to the process where a proton is raised to the vacant proton level of an HsO molecule from a lower occupied proton level of a species of molecule or molecular ion in each case the value of J gives the amount by which this initially occupied level lies below the vacant level of H20. Obviously, using these values, it is at once possible to map out a chart of the proton levels of these various particles in aqueous solution, as has been done in Fig. 36. The two exceptions in Table 9 are the values derived from the KB of glycine and alanine. In these cases, as shown in (125), a proton is transferred to a vacant level from the ordinary occupied proton level in a water molecule the value of J gives the amount by which the vacant level lies above this occupied proton level of H20. 

In Fig. 37 two areas have been shaded. The area in the upper left corner, where protons in occupied levels are unstable, we have already discussed. In the lower right-hand corner the shaded area is one where vacant proton levels cannot remain vacant to any great extent. In aqueous solution any solute particle that has a vacant proton level lower than that of the hydroxyl ion will capture a proton from the solvent molecule, since the occupied level of the latter has the same energy as the vacant level of a hydroxyl ion. Consequently any proton level that would lie in this shaded area will be vacant only on the rare occasions when the thermal agitation has raised the proton to the vacant level of a hydroxyl ion. On the other hand, there are plenty of occupied proton levels that lie below the occupied level of the H2O molecule. For example, the occupied level of the NH3 molecule in aqueous solution lies a long way below that of H20. 

In Fig. 38 it will be seen that for the (H2PO4)- ion there are two entries, one for its occupied proton level and one for its vacant proton level. In the aqueous solution of Nal PCh under consideration the thermal agita-... 

Even recent textbooks mention only the traditional view that if water were not dissociated at all, hydrolysis would not occur. From Fig. 30, however, it is quite clear that in the proton transfer (150) we are concerned with the gap between the occupied proton level of the (NJIi)+ ion and the vacant level of the H2O molecule near the top of the diagram. The existence of the vacant proton level of the (OII) ion, near the bottom of the diagram, is irrelevant. 

Furthermore, since in Sec. 121 we found the value J = 0.36 electron-volt for the proton transfer (211), this gives the occupied proton level of the (HCOOII2)+ ion a position at (0.52 — 0.36) = 0.16 electron-volt above that of the (H30)+ ion in formic acid as solvent. This is shown in Fig. 65, where, for comparison, a diagram for proton levels in aqueous solution has been included, the level of the (H30)+ ion in aqueous solution being drawn opposite to the level of the same ion in formic acid solution. This choice is quite arbitrary, but was made in order to show more clearly that we may expect that one or more acids that are strong... 

If the occupied proton level of the CH3COOH molecule dissolved in liquid ammonia lies above the vacant level of NH3, as it does in aqueous solution, acetic acid should be a strong acid in liquid ammonia. This is found to be the case the carboxylic acids are strong acids in this solvent, the protons being transferred to NH3 to form (NH4)+. 

Let us now ask where the vacant proton level must lie, in order that an indicator molecule shall be suitable for use in a very dilute acid solution —where the ratio [Ha0+]/[H20] will be very small compared with unity. According to (216) in order that [BH+]/[B] shall be near unity, obviously J must have a large negative value in other words, the vacant proton level of the molecule B must lie considerably below the occupied proton level of (HaO)+ otherwise, an insufficient crop of (BII)+ ions will be obtained. 

In Table 39 this value is recorded at the bottom of column 3. We have already found above that Ji is equal to —0.268 electron-volt. We find then Ji = (—0.268 + 0.076) = —0.192. This is the amount by which the vacant proton level lies below the occupied proton level of the (HjO)+ ion the value is included in column 2 of Table 39. 

As for the proton level in gaseous molecules of hydrogen chloride, HClmc, the following reaction cycle (Fig. 3-2) may be used to estimate the occupied proton level of HClwc at Ph (ho,d) = this also represents the vacant proton level... 

Fig. 3-Z Energy of ionic dissociation of gaseous HCl molecules and proton levels h-= proton level fiH.ojci.D)= unitary occupied proton level (donor level) in gaseous HC(L molecules Xj4.,n-, = unitary vacant proton level (acceptor level) of gaseous Cl ions.

Fig. 3-16. Hie unitary levels of acidic proton HgOVIIjO and basic proton HgO/OH in pure water, and proton transfer between two levels Copl = occupied proton level cvpl = vacant proton level fiH cHgo-. D) = unitary occupied (donor) level of acidic proton, 1h (H20.a> = unitary vacant (acceptor) level of acidic proton.

For the acidic proton transfer of Eqn. 3-44, the proton solvation processes of Eqns. 3-32 and 3-42 are represented by the proton level versus concentration curves of Eqns. 3-39 and 3-43, respectively, as shown in Fig. 3-19. In this proton level diagram, the proton level in an acetic acid solution is given by the intersecting point (mH,o - where cross each other the occupied proton level versus concentration curve of H3O ion and the vacant proton level versus concentration curve of Ac" ion, as expressed in Eqn. 3-46 ... 

Since acetic acid is a weak add with its unitary proton level (HAc/Ac") lower than the unitary addic proton level (H30 /H20), the proton moves from the unitary occupied acidic proton level to the unitary vacant proton level of acetic acid, thereby reducing the concentration of H3O" ions toward the acetic acid. Contrastively, in strong adds such as hydrochloric add whose unitary proton level (HC1/C1 ) is higher than the unitary addic proton level, the proton moves from the occupied proton level of hydrochloric acid to the vacant level of acidic proton ( H30 /H20 ), thereby increasing the concentration of H3O ions. 

Fig. 9-22. Unitary proton levels of hydrated and adsorbed hydronium ions (acidic proton) and of hydrated and adsorbed water molecules (basic proton) the left side is the occupied proton level (the real potential of acidic protons), and the right side is the vacant proton level. Hi/HjO) = unitary occupied proton level of adsorbed hydronium ions (acidic proton level) H20.d = unitary vacant proton level of adsorbed hydronium ions (acidic proton level) and unitary occupied proton level of adsorbed water molecules (basic proton level) OH = unitary vacant proton level of adsorbed water molecules (basic proton level) (pHi, ) = hydrated proton level at iso-electric point pR...

Equation 9-72 indicates that the logarithm of the ratio of the concentrations of adsorbed protons (acidic occupied proton level) to adsorbed hydroxide ions (basic vacant proton level) depends linearly on the pH of the solution. 

The pH at which the concentration of acidic occupied proton levels of adsorbed h3dronium ions equals the concentration of basic vacant proton levels of adsorbed water molecules is called the iso-electric point pHi, here, the net interfacial charge of adsorbed ions at the interface is zero. The iso-electric point pH,, is expressed in Eqn. 9-73 ... 

FIGURE 22.3 Energy levels of protons and proton vacancies in aqueous solution showing the ionic dissociation of water molecules aH+ = occupied proton level (donor), o[i = vacant proton level (acceptor), and a0 = the standard level. 

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