November 25, 2024, 11:46:17 AM
Forum Rules: Read This Before Posting


Topic: How will each of these additions change the pH of the solution?  (Read 1489 times)

0 Members and 1 Guest are viewing this topic.

Offline anastasiaaleexev

  • New Member
  • **
  • Posts: 3
  • Mole Snacks: +0/-0
1. Adding NaNO3 to a HNO3 solution
2. Adding NaCN to a HCN solution
3. Adding NaOH to a NH3 solution

I said that all 3 will increase in pH. Is that correct?

Offline chenbeier

  • Sr. Member
  • *****
  • Posts: 1337
  • Mole Snacks: +102/-22
  • Gender: Male
Re: How will each of these additions change the pH of the solution?
« Reply #1 on: March 18, 2020, 02:15:28 AM »
No.1 I would think again. No.2 is also questionable, regarding built up of a buffer.
No.3 is correct.

Offline anastasiaaleexev

  • New Member
  • **
  • Posts: 3
  • Mole Snacks: +0/-0
Re: How will each of these additions change the pH of the solution?
« Reply #2 on: March 18, 2020, 02:49:52 AM »
My thinking was that when you add NaNO3 and the NaCN, you will be increasing the concentration of the products (NO3- and CN-), so the equilibrium will shift to the reactants, causing [H+] to decrease.

Since this is incorrect, what would be the explanation for it?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27862
  • Mole Snacks: +1813/-412
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: How will each of these additions change the pH of the solution?
« Reply #3 on: March 18, 2020, 03:59:54 AM »
A lot depends on how much detailed answer you are seeking, you asked in a High School forum, so I assume HS level.

In the case of a strong acid adding salt doesn't matter at all - it is still fully dissociated and (assuming there were no volume/concentration changes) pH doesn't change. In reality it is a bit more complicated.

You are right with 2. though, yes, presence of CN- will shift the dissociation and the pH will go up.

3. is OK as well.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline anastasiaaleexev

  • New Member
  • **
  • Posts: 3
  • Mole Snacks: +0/-0
Re: How will each of these additions change the pH of the solution?
« Reply #4 on: March 18, 2020, 07:39:34 AM »
Got it, thank you! :)

Sponsored Links