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Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: sundrops on October 05, 2005, 10:47:58 PM

Title: Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 05, 2005, 10:47:58 PM

ok so I'm preparing solutions. I have 10mL of 0.150M Fe³⁺ and 5mL of 0.0005M  SCN- and 10mL of 0.10 M HNO₃

my question is, how do I determine the concentration of Fe³⁺ in the solution?

0.150 mol/L * 0.01L = 0.0015mol Fe³⁺
o.oo15mol Fe³⁺ / .025L = 0.06M Fe³⁺

Does that look about right?

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 05, 2005, 10:49:21 PM

well apparently pink writing is UNREADABLE - so I'll copy and paste my post ::)

ok so I'm preparing solutions. I have 10mL of 0.150M Fe3+ and 5mL of 0.0005M  SCN- and 10mL of 0.10 M HNO3

my question is, how do I determine the concentration of Fe3+ in the solution?

0.150 mol/L * 0.01L = 0.0015mol Fe3+
o.oo15mol Fe3+ / .025L = 0.06M Fe3+

Does that look about right?
 
 
 

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: mike on October 05, 2005, 10:52:18 PM

yes.

can also use:

C1V1 = C2V2

C = concentration (1 = initial, 2 = final)
V = volume (1 = initial, 2 = final)

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 05, 2005, 11:02:18 PM

just checking  ;D

thanks! :D

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 06, 2005, 01:26:38 AM

alrighty so we determined how to find the concentration of Fe³⁺ and I found the concentration of SCN- in the same way.

But now I need to determine the final concentration of FeSCN²⁺ but I'm not sure how to go about finding it.

any suggestions?

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 06, 2005, 01:28:52 AM

I know that all the SCN- will be used in forming the FeSCN²⁺, does that have anything to do with the final concentration of this compound?

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: Borek on October 06, 2005, 05:00:26 AM

Quote from: sundrops on October 05, 2005, 10:49:21 PM

well apparently pink writing is UNREADABLE - so I'll copy and paste my post

So use black. I know it is boring, but it is perfectly readable ;)

You may assume that SCN^- reacted completely with Fe³⁺ - and treat is as a limiting reagent question. Then check if the change in the final concentration of Fe³⁺ (after dilution) is not below the significant digits level.

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 06, 2005, 11:31:24 AM

but how do I determine [FeSCN2+]?
I cannot treat it as a limiting reactant if I do not have the concentration of the product?
product being: [FeSCN2+]

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: sundrops on October 06, 2005, 11:40:23 AM

does [SCN-] = [FeSCN2+]?

Title: Re:Concentration Question (mol/L obviously... lol)
Post by: Borek on October 06, 2005, 11:51:45 AM

Quote from: sundrops on October 06, 2005, 11:40:23 AM

does [SCN-] = [FeSCN2+]?

Write down reaction equation between Fe²⁺ and SCN^-. Amounts of both substrates are given in the question. This IS a limiting reagent question - you just have to convert concentrations to moles and moles to concentrations when needed.