Sodium standard state

Sodium chloride is formed from the elements in their standard states with a heat of formation of -411 kj mol-1 ... 

As the enthalpy of the dissolved sodium chloride in its standard state according to Henry s law is that of the infinitely dilute solution, A// , for the reaction in Equation (20.74) is... 

J- for Hydroxide Solutions in Aqueous Ethanol. From the pK2(H20) values and values of log CArCH(OH)cr/CArCHO a a given Coh- in a given solvent mixture, it is possible to calculate J- values for the solvent mixture under consideration using Equation 1 where pKw is the autoprotolytic constant of water and pK2(H20) is inserted for pK2- This definition expresses J values with reference to a standard state in pure water, and therefore basicities of sodium hydroxide solutions in mixed solvents can be compared to basicities of sodium hydroxide solutions in water by J values. 

Sodium ion acts as a spectator ion and is not involved in the electrode reactions. Thus, the sodium chloride solution is converted to a sodium hydroxide solution as the electrolysis proceeds. The minimum potential required to force this nonspontaneous reaction to occur under standard-state conditions is 2.19 V plus the overvoltage. 

Calculation From the Standard Test Dilution, plot the volume of 0.1 A sodium hydroxide titrated against time. Using only the points that fall on the straight-line segment of the curve, calculate the mean acidity released per min by the Assay Test Dilution. Taking into consideration dilution factors, calculate the lipase activity of the Standard Test Dilution, using the lipase activity of the USP Pancreatin Reference Standard stated on the label. 

Figure 2 makes it clear that —log y falls slowly as hydrochloric acid replaces a part of the sodium chloride in seawater I. The linear variation is in accord with Hamed s rule, and the magnitude of the drop is a measure of —log ynci referred to the new standard state. The behavioral similarity between seawater I and 0.66M sodium chloride is illustrated by the fact that the values of log ynci for these two solvents at Hci = 0.06 mole/kg are —0.001 and —0.002, respectively. 

Many chemical experiments are carried out in aqueous solutions and it is important to be able to define activities in these circumstances. However, the standard state we have used so far—the pure liquid at one atmosphere pressure—is singularly inappropriate. We usually wish to express concentrations in molality (moles per kilogram of solvent) and for an electrolyte, such as sodium chloride, the pure-liquid state at room temperature is not a suitable reference state. 

An element in its standard state is assigned a AH° of zero. For example, note that AH° = 0 for Na( ), but AH° = 107.8 kJ/mol for Na( ). These values mean that the gaseous state is not the most stable state of sodium at 1 atm and 298.15 K, and that heat is required to form Na(g). Note also that the standard state of chlorine is Ch molecules, not Cl atoms. Several elements exist in different forms, only one of which is the standard state. Thus, the standard state of carbon is graphite, not diamond, so AH° of C(graphite) = 0. Similarly, the standard state of oxygen is dioxygen (O2), not ozone (O3), and the standard state of sulfur is Sg in its rhombic crystal form, rather than its monoclinic form. 

The standard state of an element is the form in which the element exists under conditions of 1 atmosphere and 25°C. (The standard state for oxygen is 02(5) at a pressure of 1 atmosphere the standard state for sodium is Na(s) the standard state for mercury is Hg(/) and so on.)... 

The idea of a standard state is equally applicable to compounds. For instance, the standard state of sodium chloride would be pure sodium chloride at a pressure of 1 atm. 

The final result of these calculations is that the heat outputs from the Mk 24 formulation, if we disregard entirely the fate of the binder, can be calculated as amounting to 2.9 kcal/g for reaction to sodium vapor, 0.1 kcal higher for sodium in standard state. If the combustion of the resin is included as part of the useful heat, 0.3 kcal/g of composition is to be added. As to the resin, one might have to take into account that at the temperature of the flame, the combustion products from the resin would hardly be those of calorimetric determination, i.e. COj, HjO, Nj, but rather CO, H O. and Nj (the dissociation of water below... 

In this case, the reaction proceeds to the right-hand side, because sodium can dissolve in molten sodium chloride and also distill out of the system. The practical consequence of these processes is that the Nernst electrode potential for the alkali or alkaline earth metal-metal ion couple will be shifted in the positive direction as a result of the metal activity being less than unity, its normally defined standard state. Hence, the overlap of the current-electrode potential profiles for the conjugate pair of processes contributing to the overall corrosion reaction becomes more probable, and corrosion occurs. 

We want to know the enthalpy for formation of the LiF lattice from its components of Li+ and F" in the gas phase. This quantity cannot be directly measured, of course. Instead, we have to obtain the lattice formation enthalpy of LiF (step 5 in Figure 6.5) by summing a number of measurable quantities. Step (-1) is the formation enthalpy of LiF when it is obtained from lithium metal and fluorine gas in the standard state. The numbers we are using here are listed in tables, in textbooks, or on the Internet. Experimentally, (-1) is obtained by reacting a weighed amount of sodium metal in a surplus of chlorine gas in a calorimeter. 

Figure 9.39 Variation of the concentration (ppm) of dissolved nickel oxide, as NiO or Ni in molten sodium sulfate as a function of the Na20 activity (standard state pure Na20) and in the presence of oxygen. T = 1200 K [24].

These measurements on sodium Rydberg states were continued and improved considerably by introducing a semiconfocal millimeter microwave cavity (see Figure 26) and stabilizing the cardnotron frequency via standard phase-lock techniques. The standing wave in the cavity made it... 

The thennodynamic standard state of a substance is its most stable pure form under standard pressure (one atmosphere) and at some specific temperature (25°C or 298 K unless otherwise specified). Examples of elements in their standard states at 25°C are hydrogen, gaseous diatomic molecules, H2(g) mercury, a silver-colored liquid metal, Hg(f) sodium, a silvery-white solid metal, Na(s) and carbon, a grayish-black solid called graphite, C(graphite). We use C(graphite) instead of C(s) to distinguish it from other solid forms of carbon, such as... 

The value shown here is the nonstandard electrode potential because, in pure water, [OH ] is l.OX 10 M, not the standard-state value of 1 M.) For example, consider the reaction of sodium in water (with the Na" /Na half-reaction reversed and donbled) ... 

So we see that the result of the calculation is consistent with the experimental result. Sodium metal will reduce water to produce hydrogen gas and aqueous hydroxide ions (all under standard-state conditions). Similar results are obtained for all the alkali metals. They are all good reducing agents. 

Although sodium chloride exists in entirely different phases (liquid and crystal) within this two-phase region, the magnitude of its chemical potential must still be the same in both phases. (This means, incidentally, that the activity coefficient of salt in the saturated solution is >1 if pure substances are taken to be the standard states.) The free energy of the saturated solution differs substantially from that of the salt crystals, however. The free energy of the liquid phase is... 

In Eq. 2.9b - Ap ° is a measure of the tendency of the dye to move from aqueous solution to fibre when it is in its standard state in each phase. Therefore, it can be regarded as the driving force in the kinetics of the sorption process. Since the dye activities in Eq. 2.9b involve the freely moving sodium ions as well as dye anions, the concentration of NaCl can influence the sorption equilibrium. -Ap ° can be determined experimentally providing concentrations of sodium ions in the fibre [Na and in the aqueous solution are known. 

The fermentation-derived food-grade product is sold in 50, 80, and 88% concentrations the other grades are available in 50 and 88% concentrations. The food-grade product meets the Vood Chemicals Codex III and the pharmaceutical grade meets the FCC and the United States Pharmacopoeia XK specifications (7). Other lactic acid derivatives such as salts and esters are also available in weU-estabhshed product specifications. Standard analytical methods such as titration and Hquid chromatography can be used to determine lactic acid, and other gravimetric and specific tests are used to detect impurities for the product specifications. A standard titration method neutralizes the acid with sodium hydroxide and then back-titrates the acid. An older standard quantitative method for determination of lactic acid was based on oxidation by potassium permanganate to acetaldehyde, which is absorbed in sodium bisulfite and titrated iodometricaHy. 

---