Acids and bases strong

Strong acids such as HNO3, HCl, and HI dissociate almost completely. If we were asked to predict the direction of such a dissociation reaction, we should say that the direction of reaction favors the dissociation of the acid. The dissociation of HI is shown below  

Now let s consider a strong base such as potassium hydroxide. Let s say the solution is 1 x 10 M. Since KOH is a strong base, it dissociates completely. So we can confidently say that the concentration of hydroxide-ion formed is also 1 X 10 M. Just like the strong acid, we can ignore the possibility of hydroxide-ion formation from water, since the self-ionization of water is negligible. Since the OH concentration is 1 x 10 , the pOH is 3. From this, we can say that the pH of this solution is close to 11, since pH + pOH =14. 

In this reaction, HCl (acid) reacts to form Cl (base). HCl and Cl can be inter-converted by the gain or loss of one proton. Such a pair is called a conjugate acid-base pain Here, Cl is the conjugate base of HCl, and HCl is the conjugate acid of Cl.  

In Section 2.6 we defined an acid as a substance that ionizes in water to produce H ions, and a base as a substance that ionizes (or dissociates, in the case of an ionic base) in water to produce OH ions. These definitions are attributed to the Swedish chemist Svante Arrhenius. Although the 

Although three of the Group 2A hydroxides Ca(0H)2, SttOH)j. and BafOHlJ are typically classiTied as Strang bases, only BatOHlz is sufficiently soluble to be used commonly in the laboratory. For any ionic compound, what does dissolve—even If it is only a tiny amount— dissociates completely. 

Strong Acids Strong Bases Strong Acids Strong Bases 

Svante August Arrhenius (1859-1927). Swedish chemist. Arrhenius made important contributions to the study of chemical kinetics and electrolyte solutions. (He also speculated that life had come to Earth fir m other planets.) Arrhenius was awarded the Nobel Prize in Chemistry in 1903. 

Arrhenius acid and Arrhenius base definitions are usefial, they are restricted to the behavior of compounds in aqueous solution. More inclusive definitions were proposed by the Danish chemist Johannes Brpnsted in 1932. A Br0nsted acid is a proton donor, and a Br0nsted base is a proton acceptor. In this context, the word proton refers to a hydrogen atom that has lost its electron—also known as a hydrogen ion (H ). Consider the ionization of the weak base ammonia (NH3). 

As we saw in Section 4.1, the seven strong acids—those that ionize completely in solution—are listed in Table 4.1. All other acids are weak acids. The strong bases are the hydroxides of Group 1A and heavy Group 2A metals. These are soluble ionic compounds, which dissociate completely 

F ig u re 4.5 Some common acids and bases. From left to right Sodium hydroxide (NaOH), ascorbic acid (CjjHgOg or, with its ionizable hydrogens written first, H2C, H, Oj), hydrochloric acid (HCl), acetic acid (HC2H3O2), and ammonia (NH3). HCl and NaOH are both strong electrolytes and exist in solution entirely as ions. Water molecules are not shown. 

The chemistry of an aqueous solution often depends critically on pH. It is therefore important to examine how pH relates to acid and base concentrations. The simplest cases are those involving strong acids and strong bases. Strong acids and bases are strong electrolytes, existing in aqueous solution entirely as ions. There are relatively few common strong acids and bases (see Table 4.2). 

We have not used equilibrium arrows for this equation because the reaction lies entirely to the right. = (Section 4.1) As noted in Section 16.3, we use H O aq) and interchangeably to represent the hydrated proton in water. Thus, we can simplify this acid ionization equation to 

Analyze and Plan Because HCIO4 is a strong acid, it is completely ionized, giving [H+] = [CIO4 ] = 0.040 M. 

Check Because [H ] lies between 1 X 10 and 1 X 10, the pH will be between 2.0 and 1.0. Our calculated pH falls within the estimated range. Furthermore, because the concentration has two significant figures, the pH has two decimal places. 

An aqueous solution of HNO3 has a pH of 2.34. What is the concentration of the acid Answer 0.0046 M 

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Acrylonitrile will polymerize violendy in the absence of oxygen if initiated by heat, light, pressure, peroxide, or strong acids and bases. It is unstable in the presence of bromine, ammonia, amines, and copper or copper alloys. Neat acrylonitrile is generally stabilized against polymerization with trace levels of hydroquinone monomethyl ether and water. 

Tlie amphoteric behavior of aluminum hydroxide, wliich dissolves readily in strong acids and bases, is shown in Figure 4. In the pH range of 4 to 9, a small change in pH towards the neutral value causes rapid and voluminous precipitation of colloidal hydroxide wliich readily fomis a gel. Gels are also fomied by the hydrolysis of organoaluminum compounds such as aluminum alkoxides (see Alkoxides, metal). 

Chemical Reactivity -/Jcflctivify with Water No reaction Reactivity with Common Materials No data Stability During Transport Stable Neutralizing Agents for Acids and Caustics Not pertinent Polymerization May occur when the product is in contact with strong acids and bases Inhibitor of Polymerization No data. 

This group is stable to strong acids and bases, TMSI, Pd-C/H2, DDQ, TBAF, and LAH at low temperatures and thus has the potential to participate in a large number of orthogonal sets/... 

You need to know the strong acids and bases to work with acid-base reactions. 

As we have pointed out, strong acids and bases are completely ionized in water. As a result, compounds such as HC1 and NaOH are strong electrolytes like NaCl. In contrast, molecular weak acids and weak bases are poor conductors because their water solutions contain relatively few ions. Hydrofluoric acid and ammonia are commonly described as weak electrolytes. 

The fact that strong acids and bases are completely ionized in water makes it relatively easy to calculate the pH and pOH of their solutions (Example 13.3). 

Neutralization A reaction between a strong acid and base to form a neutral solution, 82... 

TABLE i.l The Strong Acids and Bases in Water Strong acids Strong bases... 

Identify common strong acids and bases (Table J.l). 

Very Dilute Solutions of Strong Acids and Bases... 

VERY DILUTE SOLUTIONS OF STRONG ACIDS AND BASES... 

Suppose we were asked to estimate the pH of 1.0 X 10 x m HCl(aq). If we used the techniques of Example 10.3 to calculate the pH from the concentration of the acid itself, we would find pH = 8.00. That value, though, is absurd, because it lies on the basic side of neutrality, whereas HC1 is an acid The error stems from there being two sources of hydronium ions, whereas we have considered only one. At very low acid concentrations, the supply of hydronium ions from the autoprotolysis of water is close to the supply provided by the very low concentration of HC1, and both supplies must be taken into account. The following two sections explain how to take autoprotolysis into account, first for strong acids and bases and then for weak ones. 

In very dilute solutions of strong acids and bases, the pH is significantly affected by the autoprotolysis of water. The pH is determined by solving three simultaneous equations the charge-balance equation, the material-balance equation, and the expression for Kw. 

For example, salts of strong acids and bases (NaCl, K2S04, etc.) do not suffer hydrolysis. 

Strong acids and bases Reactive wastes Ignitable wastes... 

Ignitable wastes Paint wastes Spent solvents Strong acids and bases... 

Solutions of substances that are good conductors of electricity are called electrolytes. Sodium chloride, the major constituent of seawater, is a strong electrolyte. Most salts, as well as strong acids and bases, are strong electrolytes because they remain in solution primarily in ionic (charged) forms. Weak acids and bases are weak electrolytes because they tend to remain in nonionic forms. Pure water is a nonconductor of electricity. 

Polyesters are, in general, organic solvent resistant. They show excellent room temperature resistance to organic solvents, such as hydrocarbons, alcohols, and chlorinated hydrocarbons. At slightly elevated temperatures of approximately 60 °C, alcohols and aromatic solvents can damage the polymer. Strong acids and bases can cause chemical damage to polyesters, as can ketones and phenols. 

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