Two chemistry questions about acid salt solutions

Let’s talk about your 4th question first:

Option B seems to be unbalanced and does not comply with atomic conservation.

The correct way to write it is:

3Ca[2+] + 6H2PO4[-] + 12OH[-] ==== Ca3(PO4)2↓ + 4PO4[3-] + 12H2O

That means there is still sodium phosphate in the solution after the reaction.

Let’s talk about the third question:

Why adding slaked lime can reduce all three substances: First, slaked lime is calcium hydroxide

First, calcium phosphate It is precipitation, and the calcium phosphate formed directly precipitates.

Second, if there are hydroxide radicals, hydrogen ions will inevitably react to form water.

Third, hydrogen phosphate will react with free hydroxide to form water and calcium phosphate precipitation.

The error in option B is that it does not indicate how much slaked lime was added. If it is excessive, then it must be true. If only a small amount is added, for example, if 1 drop is added to a 10-ton solution, then C is also true. B is a joke.

B I made a mistake in my answer, please change it immediately. That’s right, the hydrolysis property of hydrogen phosphate should be greater than the ionization property, so hydrogen phosphate > hydroxide > hydrogen ion. No matter how large the hydrolysis is, it will be quite small compared to the content of its own ions, unless a large number of external conditions disrupt its balance.

Option C, after adding slaked lime, the ionization reaction equation does move to the right, but have you ever thought about the fact that the insoluble substances cause these ions to precipitate and eventually the solution can only be strongly alkaline (KOH) , so hydrogen ions. . . .