Solutions of acids or bases containing

Normality (N) is the number of equivalents of the solute per liter of solution. A1.0 N solution of acid (or base) contains one equivalent of an acid (or base) per liter of solution. A 1.0 M solution of HCl is 1.0 N, but a 1.0 M solution of H2SO4 is 2.0 N. Sulfriric acid has two acidic hydrogens, and the molarity is multiplied by a factor of 2. Phosphoric acid (H3PO4) is triprotic (having three protons it can donate) and a 1.0 molar solution is 3.0 normal. 

Solutions of Acids or Bases Containing a Common Ion Equilibrium Calculations... 

When preparing solutions of acids or bases, place water in the container first. 

A titration requires a solution whose concentration is known. In Example the NaOH solution used as the titrant was known to be 0.1250 M. A titrant of known concentration is known as a standard solution, and the concentration of such a solution is determined by a standardization titration. In a standardization titration, the solution being titrated contains a known amount of acid or base. An excellent acid for standardization is potassium hydrogen phthalate, KHCg H4 O4. This substance, a carboxylic acid that contains one weakly acidic hydrogen atom per molecule, is easily obtained as a highly pure solid. A known number of moles can be weighed on an... 

In a typical acid-base titration (Section 3.10), a solution containing a known concentration of base (or acid) is added slowly from a buret to a second solution containing an unknown concentration of acid (or base). The progress of the titration is monitored, either by using a pH meter (Figure 16.6a) or by observing the color of a suitable acid-base indicator. With a pH meter, you can record data to produce a pH titration curve, a plot of the pH of the solution as a function of the volume of added titrant (Figure 16.6b). 

A buffer solution (or a buffered solution) is a solution that is resistant to change when small amounts of acid or bases are added. Such a solution contains relatively large amounts of both a weak acid (or weak base) and its strong salt (one that ionizes very well). If a small amount of a strong acid (or base) is added to a buffer, most of the added H+ (or OH-) will combine with an equivalent amount of the weak base (or acid) of the buffer to form the conjugate acid (or base) of that weak base (or acid). The result is that the hydrogen ion and hydroxide concentrations in the solution display very little change. 

The amount of acid or base that a buffer solution can neutralize before dramatic pH changes begins to occur is called its buffering capacity. Blood and seawater both contain several conjugate acid-base pairs to buffer the solution s pH and decrease the impact of acids and bases on living things. 

As mentioned before, a buffer solution contains a mixture of a weak acid and its conjugate base or of a weak base and its conjugate acid. The important aspect of the buffer solution is that the pH of the solution is minimally changed when small amounts of acid or base are added or when the solution is slightly diluted. Let us now examine a buffer solution made of a weak acid HA (0.3 M), whose pKa is 4.90, and its conjugate base NaA (0.3 M). A small quantity of HC1 (0.05 M) is accidentally added to the solution. The conjugate base (A-) will react with H+ as follows ... 

Buffered solutions are simply solutions of weak acids or bases containing a common ion. The pH calculations for buffered solutions require exactly the same procedures previously introduced in Chapter 7. This is not a new type of problem. 

The normality of a solution of an acid or base is the number of equivalents of acid or base per liter a 1 solution contains 1 equivalent per liter of solution. By determining, with use of an indicator, such as litmus, the relative volumes of acidic and alkaline solutions which are equivalent the normality of one solution can be calculated from the known value of the other. This process of acid-base titration (the determination of the titer or strength of an unknown solution), with use of special apparatus such as graduated burets and pipets, is an important method of volumetric quantitative analysis. 

Blood and other physiological solutions are buffered the pH of blood changes only slowly from its normal value (about 7.4) on addition of acid or base. Important among the buffering substances in blood are the serum proteins (Chap. 30), which contain bask and acidic groups which can combine with the added acid or base. 

That crosslinking has indeed occurred is confirmed by the very existence of aggregates at 25 °C, as in its absence the diblock copolymers are completely soluble at this temperature. Tunability of the solubility of the PMEMA block in water arises from the fact that its lower critical solution temperature (LCST) lies between 25 and 60 °C. This reversible hydration of the core could be a very useful feature to trigger release of occluded guest molecules from the core interior. More recently, utilizing a similar methodology, zwitterionic shell-crosslinked systems have also been prepared wherein the core and shell domains contain amine and carboxylic acid groups, respectively, or vice versa. Such systems exhibit an isoelectric point, at a pH wherein the crosslinked micelles ( 40 nm) become electrically neutral and precipitate out in water addition of acid or base causes complete redissolution of these nanospheres [58]. 

Standard acid or base solutions can also be prepared with ion-exchange resins. Here, a solution containing a known mass of a pure compound, such as sodium chloride, is washed through the resin column and diluted to a known volume. The salt liberates an equivalent eunount of acid or base from the resin, permitting calculation of the molarity of the reagent in a straightforward way. 

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