Decide whether an aqueous solution of each of the following salts has a pH equal to, greater than, or less than 7. If pH . 7
or pH , 7, write a chemical equation to justify your answer.
(a) NH4Br; (b) Na2CO3; (c) KF; (d) KBr; (e) AlCl3; (f) Cu(NO3)2.
How do we solve this problem?
6D.11
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DarrenKim_1H
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Re: 6D.11
I would go about answering this question by first asking myself: Does this molecule form an acidic or basic solution when it reacts with water?
For example, in part a where you're given NH4Br, you know that NH4+ is the conjugate acid for weak base NH3 such that:
NH4^+ + H2O -> NH3 + H3O+.
Hence, since it is an acid, pH < 7
A tricky part of this question is KBr, which is actually a neutral solution. This is because K+ is a weak acid and Br- is a weak base so neither are strong enough to pull apart an H2O molecule, so the solution remains neutral
For example, in part a where you're given NH4Br, you know that NH4+ is the conjugate acid for weak base NH3 such that:
NH4^+ + H2O -> NH3 + H3O+.
Hence, since it is an acid, pH < 7
A tricky part of this question is KBr, which is actually a neutral solution. This is because K+ is a weak acid and Br- is a weak base so neither are strong enough to pull apart an H2O molecule, so the solution remains neutral
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