April 28, 2024, 06:12:18 PM
Forum Rules: Read This Before Posting


« previous next »
Pages: [1]   Go Down

Topic: Dilution of a Base -> changes pH??  (Read 7389 times)

0 Members and 1 Guest are viewing this topic.

Beetle

  • Guest
Dilution of a Base -> changes pH??
« on: May 31, 2005, 05:49:57 AM »
Hey,

I've got a chem problem and it asks me to dilute 25mL of .1M NaOH until it has a pH of 9.01 and to work out the new volume of base. I keep coming up with the an answer of about 244 L does this seem reasonable?

(actual Question is: What volume of H20 must be added to 25mL of .1M NaOH to produce a solution with pH 9.01?)

Any help would be greatly appreciated

Thanx :)
Logged

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7979
  • Mole Snacks: +555/-93
  • Gender: Male
Re:Dilution of a Base -> changes pH??
« Reply #1 on: May 31, 2005, 06:10:32 AM »
pOH=4.99
Logged
AWK

Beetle

  • Guest
Re:Dilution of a Base -> changes pH??
« Reply #2 on: May 31, 2005, 06:30:26 AM »
pOH=-log[OH-]
therefore
10^-4.99=[OH-]=1.02e-5moles/litre

in 25mL there is .1 x .025 moles of NaOH = 2.5e-3
therefore for [OH-] to be 1.02e-5 the total vol must be:

2.5e-3/1.02e-5 = 244.3Litres


Is that close to correct??

Thank you for your help


Logged

Offline AWK

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 7979
  • Mole Snacks: +555/-93
  • Gender: Male
Re:Dilution of a Base -> changes pH??
« Reply #3 on: May 31, 2005, 08:12:05 AM »
It is better to use a formula c1 x V1 = c2 x V2
where V2 is a final volume. Volume of water = V2 - V1

Your result is just the final volume. Of course, taking into account significant figures, 25 mL does not matter.
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:Dilution of a Base -> changes pH??
« Reply #4 on: May 31, 2005, 08:14:45 AM »
Quote from: Beetle on May 31, 2005, 06:30:26 AM
2.5e-3/1.02e-5 = 244.3Litres

Is that close to correct??

Seems OK to me.
Logged
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info
Pages: [1]   Go Up
« previous next »
Sponsored Links