August 10, 2022, 06:58:06 AM
Forum Rules: Read This Before Posting


Topic: Question about Solubility Products  (Read 11509 times)

0 Members and 1 Guest are viewing this topic.

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Question about Solubility Products
« on: December 03, 2006, 05:52:56 PM »
Hey, I've just got a quesiton about soulbility products:

"One of the substances responsible for "hardness" of water is CaSO4. If a particular sample has 131 ppm of CaSO4, approximitly what fraction of water must be evaporated before CaSO4 (s) begins to deposit? Assume 1.0 L of water."

Thanks guys

Offline Dan

  • Retired Staff
  • Sr. Member
  • *
  • Posts: 4716
  • Mole Snacks: +469/-72
  • Gender: Male
  • Organic Chemist
    • My research
Re: Question about Solubility Products
« Reply #1 on: December 03, 2006, 05:56:08 PM »
Show your attempt. How do you think you could work it out?
My research: Google Scholar and Researchgate

Offline Donaldson Tan

  • Editor, New Asia Republic
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3177
  • Mole Snacks: +261/-13
  • Gender: Male
    • New Asia Republic
Re: Question about Solubility Products
« Reply #2 on: December 03, 2006, 06:38:04 PM »
You will need the solubility product constant of calcium sulphate.
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #3 on: December 04, 2006, 07:28:41 PM »
ok well so far, I've recognized that CaSO4 is highly soluble in water. I would have to evaporate almost all of it before I would get any precipitation.

If I ignore supersaturation, a solute will begin to precipitate out of solution when its concentration exceeds its solubility.

But how do I include the math part to this quesiton?

*Also, thanks to Geodome, I need the solubility product constant as well, which is: 4.93 x 10^-5

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27142
  • Mole Snacks: +1762/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question about Solubility Products
« Reply #4 on: December 04, 2006, 07:36:09 PM »
ok well so far, I've recognized that CaSO4 is highly soluble in water.

It is not.

Quote
I need the solubility product constant as well, which is: 4.93 x 10^-5

So you know it, not need it :)

It is enough to take a look at the solubility product to see that saturated solution concentration must be below 0.01M - hardly much.

What is definition of solubility product?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Donaldson Tan

  • Editor, New Asia Republic
  • Retired Staff
  • Sr. Member
  • *
  • Posts: 3177
  • Mole Snacks: +261/-13
  • Gender: Male
    • New Asia Republic
Re: Question about Solubility Products
« Reply #5 on: December 05, 2006, 05:44:13 AM »
But how do I include the math part to this quesiton?

Don't you know the equilibrium expression relating to the solubility product constant?

You need to convert 131ppm to mol/dm3, ie. 131ppm = Y mol/dm3 (note ppm is mass ratio)

Ksp = [Ca2+][SO42-]

Find the saturated concentration of calcium sulphate from the above expression, which should be larger than Y.

From here, you should be able to derive the required fraction of water to be evaporated using the mass balance of calcium sulphate.

« Last Edit: December 05, 2006, 05:49:37 AM by geodome »
"Say you're in a [chemical] plant and there's a snake on the floor. What are you going to do? Call a consultant? Get a meeting together to talk about which color is the snake? Employees should do one thing: walk over there and you step on the friggin� snake." - Jean-Pierre Garnier, CEO of Glaxosmithkline, June 2006

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #6 on: December 05, 2006, 09:13:51 PM »
wait. would the chemical equation just be the decomposition of CaSO4? so CaSO4 ----> Ca + SO4 ?
Or do i have to add water into this equation?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27142
  • Mole Snacks: +1762/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question about Solubility Products
« Reply #7 on: December 06, 2006, 04:46:53 AM »
Ca + SO4

These are ions (Ca2+ & SO42-). And no such compound as SO4.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #8 on: December 06, 2006, 04:12:29 PM »
ok. well Geodome says to convert 131 ppm into Y mol/dm3

but I have a problem here. My teacher did not even teach us about dm3 or dm3 conversion, so i am completely unfamiliar with the term dm3. Is that density or something? I was hoping that there is another way to convert 131 ppm into just mols or something. And is "Y" just a variable?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27142
  • Mole Snacks: +1762/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question about Solubility Products
« Reply #9 on: December 06, 2006, 05:10:16 PM »
Y is just a variable (or an unknown if you prefer), dm3 is the same as L. dm is a length measure - 1/10th of a meter. dm3 is dm cubic.

http://en.wikipedia.org/wiki/Deci
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #10 on: December 06, 2006, 05:22:20 PM »
ok. well before i do all this i still need to make the chemical equation.
My equation goes like this:

CaSO4 + H2O ------> CaO + H2(SO4)

is this right or am i doing something wrong?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27142
  • Mole Snacks: +1762/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question about Solubility Products
« Reply #11 on: December 06, 2006, 06:06:22 PM »
I am afraid your reaction is completely wrong. First: this is ionic compound that gets dissolved to ions. Two: you need net ionic reaction, as it will help determine how the solubility product for CaSO4 looks alike.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #12 on: December 06, 2006, 06:21:41 PM »
Okay, so its an ionic compound. THe net-ionic equation would be:

CaSO4(s) <---> Ca2+ + SO42-

and so:

Qsp= [Ca2+] [SO42-]

so i somehow find thhe concentrations of both Ca and SO4 and sub them into that Qsp equation to find Qsp?

Offline Borek

  • Mr. pH
  • Administrator
  • Deity Member
  • *
  • Posts: 27142
  • Mole Snacks: +1762/-405
  • Gender: Male
  • I am known to be occasionally wrong.
    • Chembuddy
Re: Question about Solubility Products
« Reply #13 on: December 06, 2006, 06:24:06 PM »
Look at the reaction equation - how is concentration of Ca2+ related to concentration of SO42- if solid CaSO4 is the only source of ions?
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

Offline Jinn21

  • New Member
  • **
  • Posts: 8
  • Mole Snacks: +0/-0
Re: Question about Solubility Products
« Reply #14 on: December 06, 2006, 06:29:39 PM »
ahh im so confused. i don't even know where to begin ???

Sponsored Links