Write a short note on strong and weak acids??
Answers
Strong acids and bases are 100% ionized in aqueous solution. Weak acids and bases are less than 100% ionized in aqueous solution. Salts of weak acids or bases can affect the acidity or basicity of their aqueous solutions.
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Define a strong and a weak acid and base....
Recognize an acid or a base as strong or weak.
Determine if a salt produces an acidic or a basic solution.
Strong and Weak Acids
Except for their names and formulas, so far we have treated all acids as equals, especially in a chemical reaction. However, acids can be very different in a very important way. Consider HCl(aq). When HCl is dissolved in H2O, it completely dissociates into H+(aq) and Cl−(aq) ions; all the HCl molecules become ions:
HCl
100%
→
H+(aq)+Cl−(aq)
Any acid that dissociates 100% into ions is called a strong acid. If it does not dissociate 100%, it is a weak acid. HC2H3O2 is an example of a weak acid:
HC2H3O2
∼5%
⟶
H+(aq)+C2H3O
−
2
(aq)
Because this reaction does not go 100% to completion, it is more appropriate to write it as a reversible reaction:
HC2H3O2⇌H+(aq)+C2H3O
−
2
(aq)
As it turns out, there are very few strong acids, which are given in Table 14.7.1. If an acid is not listed here, it is a weak acid. It may be 1% ionized or 99% ionized, but it is still classified as a weak acid.
Any acid that dissociates 100% into ions is called a strong acid. If it does not dissociate 100%, it is a weak acid.
Table 14.7.1: Strong Acids and Bases
HCl
LiOH
HBr
NaOH
HI
KOH
HNO3
RbOH
H2SO4
CsOH
HClO3
Mg(OH)2
HClO4
Ca(OH)2
Sr(OH)2
Ba(OH)2
Strong and Weak Bases
The issue is similar with bases: a strong base is a base that is 100% ionized in solution. If it is less than 100% ionized in solution, it is a weak base. There are very few strong bases (Table 14.7.1); any base not listed is a weak base. All strong bases are OH– compounds. So a base based on some other mechanism, such as NH3 (which does not contain OH− ions as part of its formula), will be a weak base.
Example 14.7.1: Identifying Strong and Weak Acids and Bases
Identify each acid or base as strong or weak.
HCl
Mg(OH)2
C5H5N
Solution
Because HCl is listed in Table 14.7.1, it is a strong acid.
Because Mg(OH)2 is listed in Table 14.7.1, it is a strong base.
The nitrogen in C5H5N would act as a proton acceptor and therefore can be considered a base, but because it does not contain an OH compound, it cannot be considered a strong base; it is a weak base.
Exercise 14.7.1
Identify each acid or base as strong or weak.
RbOH
HNO
2
Answer a
Answer b
Example 14.7.2: Characterizing Base Ionization
Write the balanced chemical equation for the dissociation of Ca(OH)2 and indicate whether it proceeds 100% to products or not.
Solution
This is an ionic compound of Ca2+ ions and OH− ions. When an ionic compound dissolves, it separates into its constituent ions:
Ca(OH)
2
→Ca2+(aq)+2OH−(aq)
Because Ca(OH)2 is listed in Table 14.7.1, this reaction proceeds 100% to products.
Exercise 14.7.2
Write the balanced chemical equation for the dissociation of hydrazoic acid (HN3) and indicate whether it proceeds 100% to products or not.
Answer a
Key Takeaways
Strong acids and bases are 100% ionized in aqueous solution.
Weak acids and bases are less than 100% ionized in aqueous solution.
Salts of weak acids or bases can affect the acidity or basicity of their aqueous solutions.
Contributions & Attributions
This page was constructed from content via the following contributor(s) and edited (topically or extensively) by the LibreTexts development team to meet platform style, presentation, and quality:
Marisa Alviar-Agnew (Sacramento City College)
Henry Agnew (UC Davis)
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14.5: Reactions of Acids and Bases 14.8: Water - Acid and Base in One
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Answer:
Strong acid has less amount of OH- ions and more amount of H+ ions whereas weak acid has more amount of OH- ions as compare to strong acids and less amount of H+ ions as compare to strong acids. pH pf strong acid is less than 5 amd pH of weak acid of less than 7 but more than 4 or 5. Example of strong acid ls are HCl , H2SO4 , etc. and example of weak acid CH3COOH, etc.