Acids strong/weak

Ion-exchange resins are categorized by the nature of functional groups attached to a polymeric matrix, by the chemistry of the particular polymer in the matrix, and by the porosity of the polymeric matrix. There are four primary types of functionaHty strong acid, weak acid, strong base, and weak base. Another type consists of less common stmctures in specialty resins such as those which have chelating characteristics. 

Of the several syntheses available for the phenothiazine ring system, perhaps the simplest is the sulfuration reaction. This consists of treating the corresponding diphenylamine with a mixture of sulfur and iodine to afford directly the desired heterocycle. Since the proton on the nitrogen of the resultant molecule is but weakly acidic, strong bases are required to form the corresponding anion in order to carry out subsequent alkylation reactions. In practice such diverse bases as ethylmagnesium bromide, sodium amide, and sodium hydride have all been used. Alkylation with (chloroethyl)diethylamine affords diethazine (1), a compound that exhibits both antihista-minic and antiParkinsonian activity. Substitution of w-(2-chloroethyl)pyrrolidine in this sequence leads to pyrathiazine (2), an antihistamine of moderate potency. 

Weak acid-strong base. When a strong base such as NaOH is added to a solution of a weak acid, HB, a two-step reaction occurs. The first step is the ionization of the HB molecule to H+ and B ions the second is the neutralization of the H+ ions produced in the first step by the OH- ions of the NaOH solution. 

Identify the type of aqueous reaction using the symbols PPT for pre-dpitation, SA/SB for strong acid-strong base, SA/WB for strong acid-weak base, WA/SB for weak acid-strong base, and NR for no reaction. 

A weak acid-strong base titration. The curve represents the titration of 50.00 mL of 1.000 M acetic acid, HC2H3O2. with 1.000 /W NaOH. The solution at the equivalence point is basic (pH = 9.22). Phenolphthalein is a suitable indicator. Methyl red would change color much too early, when only about 33 mL of NaOH had been added. Bromthymol blue would change color slightly too quickly. 

A typical weak acid-strong base titration is that of acetic acid with sodium hydroxide. The net ionic equation for the reaction is... 

From Figure 14.6 and Example 14.8, it should be clear that the indicator used in this titration must change color at about pH 9. Phenolphthalein (end point pH = 9) is satisfactory. Methyl red (end point pH = 5) is not suitable. If we used methyl red, we would stop the titration much too early, when reaction is only about 65% complete. This situation is typical of weak acid-strong base titrations. For such a titration, we choose an indicator that changes color above pH 7. 

Strategy Once you realize that this is a weak acid-strong base titration, the problem unravels follow the rules cited in Table 14.3. 

STRONG ACID-WLAK BASE AND WEAK ACID-STRONG BASE TITRATIONS... 

Strong Acid-Weak Base and Weak Acid-Strong Base Titrations... 

C17-0019. Classify each of the following substances as a weak acid, strong acid, weak base, strong base, or neither an acid nor a base (a) HCIO4 (b) NaOH (c) CH3 OH (d) C2 H5 CO2 H and (e) C2H5 NH2. 

Strong acid + strong base Weak acid + strong base Strong acid + weak base Weak acid + weak base... 

When an acid in solution is exactly neutralized with a base the resulting solution corresponds to a solution of the salt of the acid-base pair. This is a situation which frequently arises in analytical procedures and the calculation of the exact pH of such a solution may be of considerable importance. The neutralization point or end point in an acid-base titration is a particular example (Chapter 5). Salts may in all cases be regarded as strong electrolytes so that a salt AB derived from acid AH and base B will dissociate completely in solution. If the acid and base are strong, no further reaction is likely and the solution pH remains unaffected by the salt. However if either or both acid and base are weak a more complex situation will develop. It is convenient to consider three separate cases, (a) weak acid-strong base, (b) strong acid-weak base and (c) weak acid-weak base. 

XIII- Weak Acid + Strong Base — Water + Conjugate Base... 

Many pesticides are moderate to weak acids. Strong acid pollutants are fully ionised at ambient pH. Examples include trifluoroacetic and chloroacetic acids, whose use as herbicides has been banned but which still occur as solvent degradation products [16], or the pesticide 2,4,5-trichlorophenoxyacetic acid (P 2.83). 

It is interesting to compare the case of a strong acid titrated with a strong base (in the last section) with the titration of a weak acid, such as acetic acid, with a strong base, such as NaOH. The difference between the weak acid-strong base case and the strong acid-strong base case just discussed is that for the same... 

If directed by your instructor, also obtain weak acid-strong base, strong base-strong acid, and weak base-strong acid titration curves. 

O OD Classify each compound as a strong acid, weak acid, strong... 

The curve for a weak acid-strong base titration The weak acid here is propanoic acid, CH3CH2COOH. 

The salt of a weak acid/strong base dissolves to form a basic solution. 

Weak acids Strong acids Weak bases Strong bases Solvents... 

Weak acids Strong acids Good behaviour... 

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