How do we tell if it is acidic?
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How do we tell if it is acidic?
Given the formula, such as Cr(ClO4)3, how do we tell if it is acidic or not?
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Re: How do we tell if it is acidic?
Since ClO4- is a conjugate base of a strong acid (very strong) it will be inactive in solution. Since Cr 3+ is not a conjugate of any strong acids or bases, you know it has to be from a weak base because the other component of the salt came from an acid. Therefore the Cr3+ is a conjugate acid of a weak base and would lower the pH of the solution, making it acidic.
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Re: How do we tell if it is acidic?
We look at the ions produced by the salt. Here are some rules I like to keep in mind:
1) Conjugate base of a strong acid (anion) = neutral
2) Conjugate acid of a strong base (cation) = neutral
3) Conjugate base of a weak acid (anion) = basic
4) Conjugate acid of a weak base (cation) = acidic
Therefore, for Cr(ClO4)3:
Cr3+ is the conjugate acid of a weak base (Cr(OH)3) - it is an acidic cation
ClO4- is the conjugate base of a strong acid (HClO4) - it is a neutral anion
Therefore, a solution of Cr(ClO4)3 is acidic.
1) Conjugate base of a strong acid (anion) = neutral
2) Conjugate acid of a strong base (cation) = neutral
3) Conjugate base of a weak acid (anion) = basic
4) Conjugate acid of a weak base (cation) = acidic
Therefore, for Cr(ClO4)3:
Cr3+ is the conjugate acid of a weak base (Cr(OH)3) - it is an acidic cation
ClO4- is the conjugate base of a strong acid (HClO4) - it is a neutral anion
Therefore, a solution of Cr(ClO4)3 is acidic.
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Re: How do we tell if it is acidic?
You have to look at the ions. The conjugate acids of a strong base and the conjugate base of a strong acid both do not affect the pH. The conjugate base of a weak acid (anion) is basic, and vice versa for the conjugate acid of a weak base.
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