Hydroxide ions weak acid-strong base

Hydroxide Ion Is a strong base and acetic acid Is a weak acid, so proton transfer from CH3 CO2 H to OH goes essentially to completion ... 

At the microscopic level, the Arrhenius theory defines acids as substances which, when dissolved in water, yield the hydronium ion (H30+) or H+(aq). Bases are defined as substances which, when dissolved in water, yield the hydroxide ion (OH). Acids and bases may be strong (as in strong electrolytes), dissociating completely in water, or weak (as in weak electrolytes), partially dissociating in water. (We will see the more useful Brpnsted-Lowry definitions of acids and bases in Chapter 15.) Strong acids include ... 

Check to see that the reaction occurs through hydrogen ion transfer from phosphoric acid molecules to hydroxide ions. Every weak acid-strong base reaction occurs by this type of H+ transfer. 

Bronsted and Lowery said that an acid reacts with a base to form conjugate acid-base pairs. Conjugate acid base pairs differ by a single H+. NH3 is a base, for example, and NH4 is its conjugate acid. H2O is an acid in the reaction between ammonia and water, and OH is its conjugate base. In this reaction, the hydroxide ion is a strong base and ammonia is a weak base, so the equilibrium is shifted to the left — there s not much hydroxide at equilibrium. 

A base is any material that produces hydroxide ions when it is dissolved in water. The words alkaline, basic, and caustic are often used synonymously. Common bases include sodium hydroxide (lye), potassium hydroxide (potash lye), and calcium hydroxide (slaked lime). The concepts of strong versus weak bases, and concentrated versus dilute bases are exactly analogous to those for acids. Strong bases such as sodium hydroxide dissociate completely while weak bases such as the amines dissociate only partially. As with acids, bases can be either inorganic or organic. Typical reactions of bases include neutralization of acids, reaction with metals, and reaction with salts ... 

Bases, like acids, are classified as strong or weak. A strong base in water solution is completely ionized to OH- ions and cations. As you can see from Table 4.1, the strong bases are the hydroxides of the Group 1 and Group 2 metals. These are typical ionic solids, completely ionized both in the solid state and in water solution. The equations written to represent the processes by which NaOH and Ca(OH)2 dissolve in water are... 

Below is the titration curve for the neutralization of 25 mL of a base with a strong monoprotic acid. Answer the following questions about the reaction and explain your reasoning in each case, (a) Is the base strong or weak (b) What is the initial hydroxide ion concentration of the base (c) What is Kh for the base (d) What is the initial concentration of the base (e) What is the concentration of acid in the titrant (f) Use Table 11.3 to select an indicator for the titration. 

An aqueous solution of potassium hydroxide contains K , OH, and H2 O. Phosphoric acid is a weak acid, so most of its molecules remain as H3 PO4 in aqueous solution. The species present at the beginning of the reaction are K and OH ions and molecules of H3 PO4 and H2 O. The hydroxide ion is a powerful base that removes all of the acidic hydrogen atoms from both strong and weak acids. 

In a weak acid or base, the backwards reaction (where ions join to form the acid or base) occurs more often than it does in a strong acid or base. Therefore, with a weak acid or base, some hydrogen and hydroxide ions are released, but there are many more molecules of intact acid or base than there would be with a strong acid or base. Most acids and bases are weak. They do not completely break down in water. 

However, attempts to make an aqueous solution of the base sodium amide would result in the formation of sodium hydroxide and ammonia. The amide ion is a strong base and abstracts a proton from water, a weak acid. The reverse reaction is not favoured, in that hydroxide is a weaker base than the amide ion, and ammonia is a weaker acid than water. Take care with the terminology amide the amide... 

Very Weak Acids and Bases. These compounds may be considered to have pATa s or pATb s in the range of 7 to 10. Since they are very weakly ionized, the initial conductance is very low. With a strong base as titrant, the curve follows the salt line from the start of the titration. Rounding of the curve in the vicinity of the endpoint takes place because of the release of OH ions by the hydrolysis of the anion formed. The weaker the add, the more pronounced this effect. After the endpoint, the conductance increases rapidly because of the excess OH ions. The endpoint is determined by extrapolating the first straight portion of the neutralization curve and the latter portion of the excess hydroxide curve. 

Barite will not react because it contains the anion (S04 ) of a strong acid (H2SO4). Brucite will react because the hydroxide ion is the conjugate base of water, a weak acid. Malachite wiU react and fizz because it contains both the carbonate ion, the conjugate base of the weak acid carbonic acid, and the hydroxide ion. 

However, weak acids do not yield many hydrogen ions and weak bases do not yield many hydroxide ions, and titration of weak acids and bases or their salts with strong acids and bases may equally well be regarded as the addition or removal of a proton ... 

In summary, weak acids and bases prefer hydrogen and hydroxide ions respectively to all others, whereas strong acids and bases prefer any other ion to hydrogen and hydroxide. This is true only for ion-exchange processes involving salts weak acids and bases are just as readily neutralised as any others by bases and acids respectively. 

The titration of a weak acid (or base) is illustrated in figure C. 14(b). The reagent used is a weak base (or acid). In other methods the end-point of such a titration would not be sharp on account of hydrolysis, but this effect does not detract from the accuracy of a conductance titration. A semi-strong acid (pK 2-4) does not give a very satisfactory end-point with either strong or weak base in this case some ammonia is added to the acid in the cell, and titration is then carried out with sodium hydroxide. This completes the neutralisation of the acid, after which the ammonium ion present is replaced by the sodium ion, with a fall in conductance. Finally the conductance rises as... 

Strong and Weak Bases Just as the acidity of an aqueous solution is a measure of the concentration of the hydronium ion, H3O+, the basicity of an aqueous solution is a measure of the concentration of the hydroxide ion, OH . The most common example of a strong base is an alkali metal hydroxide, such as sodium hydroxide, which completely dissociates to produce the hydroxide ion. 

As the titration begins, mostly HAc is present, plus some H and Ac in amounts that can be calculated (see the Example on page 45). Addition of a solution of NaOH allows hydroxide ions to neutralize any H present. Note that reaction (2) as written is strongly favored its apparent equilibrium constant is greater than lO As H is neutralized, more HAc dissociates to H and Ac. As further NaOH is added, the pH gradually increases as Ac accumulates at the expense of diminishing HAc and the neutralization of H. At the point where half of the HAc has been neutralized, that is, where 0.5 equivalent of OH has been added, the concentrations of HAc and Ac are equal and pH = pV, for HAc. Thus, we have an experimental method for determining the pV, values of weak electrolytes. These p V, values lie at the midpoint of their respective titration curves. After all of the acid has been neutralized (that is, when one equivalent of base has been added), the pH rises exponentially. 

Consider now the salt of a strong acid and a weak base class (3). Here the initial high concentration of cations M + will be reduced by combination with the hydroxide ions of water to form the little-dissociated base MOH until the equilibrium ... 

FIGURE 1.3 The net ionic equation for the neutralization of HCN, a weak acid, by the strong base NaOH, tells us that the hydroxide ion extracts a hydrogen ion from an acid molecule. 

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