April 30, 2024, 12:06:02 AM
Forum Rules: Read This Before Posting


« previous next »
Pages: [1]   Go Down

Topic: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture  (Read 3667 times)

0 Members and 1 Guest are viewing this topic.

Offline wolfnote

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« on: April 23, 2016, 01:32:31 PM »
I have 0.0150M NaH2PO4 and 0.0250M Na2HPO4 in my lab.  What would the pH be of a mixture of 100.0 ml of each?

I got stuck on this one because I am dealing with two separate mixture calculations that have to be brought together into one.  My reasoning is guided by Henderson-Hasselbach equation that states:
pH = pKa + log 10 [base]/Acid

However , I am intimidated somehow by this problem and do not know how to approach it.
Logged

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27665
  • Mole Snacks: +1801/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #1 on: April 23, 2016, 01:39:27 PM »
HH equation is exactly what is needed here. Just decide what is the acid and what is the base, and plug numbers.
Logged
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline wolfnote

  • Very New Member
  • *
  • Posts: 2
  • Mole Snacks: +0/-0
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #2 on: April 23, 2016, 01:54:21 PM »
What is the criteria that I would use in deciding which one is acid and which one is base?
Logged

Offline Babcock_Hall

  • Chemist
  • Sr. Member
  • *
  • Posts: 5614
  • Mole Snacks: +322/-22
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #3 on: April 23, 2016, 06:51:54 PM »
I suggest drawing out the structures of the two chemical species.
Logged

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7979
  • Mole Snacks: +555/-93
  • Gender: Male
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #4 on: April 23, 2016, 08:08:39 PM »
Just write down Ka and Kb for both ions.
The higher Ka => acid
The higher Kb => base
Or do carefully analogous reasoning on pKa and pKb.
Logged
AWK

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27665
  • Mole Snacks: +1801/-410
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #5 on: April 24, 2016, 02:51:59 AM »
Quote from: wolfnote on April 23, 2016, 01:54:21 PM
What is the criteria that I would use in deciding which one is acid and which one is base?

Do you know Bronsted-Lowry definitions of acids and conjugate bases?
Logged
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info

Offline raylab13

  • New Member
  • **
  • Posts: 3
  • Mole Snacks: +0/-0
Re: PH Calculation Of NaH2PO4 and Na2HPO4 Mixture
« Reply #6 on: April 25, 2016, 12:41:46 AM »
Which one has more H+ to donate? That one is the acid. The other one is the base.
Logged
Pages: [1]   Go Up
« previous next »
Sponsored Links