textbook problem 6D #11

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Kaylee Nezwek 1D
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textbook problem 6D #11

Postby Kaylee Nezwek 1D » Thu Dec 10, 2020 7:11 pm

hey! 6D #11 in the textbook asks to determine whether an aqueous solution of the following salts have pH =7, >7, or <7, and to write an equation to justify: a.) NH4Br, b.) Na2CO3, c.) KF, d.) KBr, e.) AlCl3, and f.) Cu(NO3). I'm really confused on how to know what the pH would be, and how to know which part of the salt we should be using in the equation to justify the answer. could someone explain how to approach this question?

Stuti Pradhan 2J
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Re: textbook problem 6D #11

Postby Stuti Pradhan 2J » Thu Dec 10, 2020 7:13 pm

In this problem, you want to see what the effect of the salt would be on the aqueous solution, so you want to understand how the salt will interact with the water molecules. Within the salt, the conjugate base of any strong acid and the conjugate acid of any strong base will have no effect on the pH, so that ion can be ignored for this purpose. Whichever ion is not the conjugate base of a strong acid or the conjugate acid of a weak base will interact with the water. If this ion has a negative, it will attract the hydrogen from the water and leave behind an OH-, making the solution basic. If the ion has a positive charge, the water will attract the hydrogen, forming an H3O+ molecule and making the solution acidic.

For example, in part a) the Br- ion in NH4Br is the conjugate acid of HBr which is a strong acid, and NH4+ is the conjugate acid of NH3, which is a weak base. Therefore, the Br- has no effect on the pH of the solution. However, the NH4+ will interact with the water, losing its electron to water to create NH3 and H3O+.

Hope this helps!

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