Solute substances

In strongly acid solution, substances which are normally reducing agents reduce sulphur dioxide solution or sulphites, for example iron(II) and zinc ... 

We discuss solutions further in the chapter on solutions and colligative properties, but solution stoichiometry is so common on the AP exam that we will discuss it here briefly also. Solutions are homogeneous mixtures composed of a solute (substance present in smaller amount) and a solvent (substance present in larger amount). If sodium chloride is dissolved in water, the NaCl is the solute and the water the solvent. 

Many reactions, particularly those that involve ionic compounds, take place in aqueous solution. Substances whose aqueous solutions contain ions and therefore conduct electricity are called electrolytes. Ionic compounds, such as NaCl, and molecular compounds that dissociate substantially into ions when dissolved in water are strong electrolytes. Substances that dissociate to only a small extent are weak electrolytes, and substances that do not produce ions in aqueous solution are nonelectrolytes. Acids dissociate in aqueous solutions to yield an anion and a hydronium ion, H30 +. Those acids that dissociate to a large extent are strong acids those acids that dissociate to a small extent are weak acids. 

There are some substances which, if left out in the atmosphere, absorb moisture but do not change their state. For example, concentrated sulfuric acid, a colourless, viscous liquid, absorbs water vapour from the air and becomes a solution. Substances which do this are said to be hygroscopic. 

When a solution is equilibrated with a pure solute, the activity of the solute in the solution is the same as the activity of the pure solute substance. Fora crystalline material in an ideal solution, solubility can be expressed by the following equation ... 

The other is the case in which the mixture is ideal when all substances but one (solvent) are at very dilute concentrations. Such mixtures are called ideal dilute solutions, for which the Henry s law (a linear relation between pi, and In x, in a limited range of dilute concentrations) holds valid and in which the equality of Eq. 5.24 is realized only for the main substance present in excess as solvent and not for the solute substances as minor constituents ... 

In this case the unitary value of the chemical potential of solute substance i can be estimated, as mentioned above, by extrapolating the chemical potential of dilute constituent i to xt = 1 from the dilute concentration range in which the linear relation of Eq. 5.22 holds. 

We bear in mind however that the values of p (T,p) and y, depend upon the choice of the ideal reference system. If we choose for the solvent a reference system in which y, becomes unity as xt approaches unity, the unitary chemical potential p (T,p) is given by the chemical potential p (T,p) of the pure solvent i ut(T,p) = p (T,p). On the other hand, if we choose for the solute substances a reference system in which y, becomes unity as xt approaches zero, the unitary chemical potential ju (r,p) is given by the chemical potential p (T,p) of the solute i at infinite dilution p ( T,p) = p (T,p). 

In contrast to a perfect solution, a solution is called an ideal solution, if Eq. 8.1 is valid for solute substances in the range of dilute concentrations only. Moreover, the unitary chemical potential p2(T,p) of solute substance 2 is not the same as the chemical potential p2( T,p) of solute 2 in the pure substance p2(T,p) p2(T,p) Henry s law. For the main constituent solvent, on the other hand, the unitary chemical potential p[( T,p) is normally set to be equal to f l p) in the ideal dilute solution p"(T,p) = p°(l p). The free enthalpy per mole of an ideal binary solution of solvent 1 and solute 2 is thus given by Eq. 8.10 ... 

Let us consider a semipermeable membrane separating a pure liquid solvent 1 from a solution containing solvent 1 and solute substances as shown in Fig. 8.2. The chemical potentials of solvent 1 in the pure solvent and in the solution, Uj and u,, are given by Eqs. 8.33 and 8.34, respectively ... 

When writing a net ionic equation, first write out all soluble substances as ions in solution. Substances that are not soluble or do not dissociate into ions completely are written as shown in the overall equation. Return to the equation 2KI(aq) + Pb(N03)2(aq)-> Pbl2(s) + 2KN03(aq). First write out the soluble substances as ions in solution ... 

Calibration solutions +/- Substance purity, old solutions, error in dilution. Poor internal standard(s) Contaminated solvent Change calibrant solutions Check purity of substances in concentrated solutions Correct for impurities Change supplier of substances/ internal standard/ serial dilution Change solvent or redistill... 

The process of enhanced solubility in micellar solutions is normally referred to as solubilization, or in the words of McBain solubilization is the term given to a particular mode of bringing into solution substances that are otherwise insoluble in a given medium. Similar definitions were proposed later, with the only significant change that solubilization includes increased solubility caused by the presence of micelles. Over the years a considerable amount of empirical information relating to solubihzation has been pubhshed. The early studies have been reviewed by McBain, Klevens, McBain and Hutchinson, and by Elworthy et ah Later developments have been described in several reviews, the most comprehensive is the book edited by Christian and Scamehom. ... 

The student of chemistry should not overlook that which is known as the colloidal state of matter. In the forerunning part of this book we learned something about solutions. Substances like sugar, salt, etc., are called crystalloids because they dre able to pass into solution and may be again restored to their original condition by evaporating the liquid in which they are dissolved. 

This theory was satisfactory when applied to crystals, but what about optical activity that persisted in solution In solution substances existed not as crys-... 

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