[terry33199]

(Fe^3+) + (SCN^-)  FeSCN^2+
5ml of .002M FE(NO)_3 , 4ml of .002M KSCN, and 1 ml of water are mixed.  the equilibrium constant of FeSCN^2+ is .000131M
How many moles of Fe^3+ and SCN^- are initially present?
How many moles of FeSCN^2+ are in the mixture at equilibrium?
How many moles of Fe^3+ and SCN^- are used up in making FeSCN^2+?

[terry33199]

That kind of showed up wrong.  I'll try again:

(Fe^3+) + (SCN^-)  <->  FeSCN^2+

5ml of .002M FE(NO)_3 , 4ml of .002M KSCN, and 1 ml of water are mixed.  the equilibrium constant of FeSCN^2+ is .000131M
How many moles of Fe^3+ and SCN^- are initially present?
How many moles of FeSCN^2+ are in the mixture at equilibrium?
How many moles of Fe^3+ and SCN^- are used up in making FeSCN^2+?

[Yggdrasil]

Please read the Forum Rules.  You should that show you've at least attempted to answer the problem before we will help you.

[terry33199]

Please read the Forum Rules.  You should that show you've at least attempted to answer the problem before we will help you.

well, i know M means mol/L.  I'm thinking that i need that to find moles somehow.

[terry33199]

for moles of Fe initially present do i multiply .002M x .001L(total volume) and get 2x10^-6

[Yggdrasil]

Yes.  You can do the same to find the moles of SCN.  For finding the concentration of FeSCN, you should use an ICE table, which you can read about in your chemistry textbook or at wikipedia:

http://en.wikipedia.org/wiki/Ice_table

ICE tables are very useful for eqilibrium problems like these.  If you have any questions after reading about ICE tables, let us know.

[terry33199]

Yes.  You can do the same to find the moles of SCN.  For finding the concentration of FeSCN, you should use an ICE table, which you can read about in your chemistry textbook or at wikipedia:

http://en.wikipedia.org/wiki/Ice_table

ICE tables are very useful for eqilibrium problems like these.  If you have any questions after reading about ICE tables, let us know.

So then the number of moles of SCN- initially present is also 2x10^-6?

If so, then would this be how to get the moles of FeSCN^2+ in the mixture at equilibrium:
.000131= FeSCN^2+ / ((2x10^-6)(2x10^-6))
then moles of FeSCN^2+ in mixture at equilibrium is 5.24x10^-16?

[Borek]

for moles of Fe initially present do i multiply .002M x .001L(total volume) and get 2x10^-6

Wrong and wrong

First of all, 4 mL + 5 mL + 1 mL is not 0.001L.

Second, why do you want to multiply iron concentration by final volume?

If you take 1 mL of 1M solution and dilute it to 1L - how much substance do you have? 0.001x1 or 1x1?

[terry33199]

for moles of Fe initially present do i multiply .002M x .001L(total volume) and get 2x10^-6

Wrong and wrong

First of all, 4 mL + 5 mL + 1 mL is not 0.001L.

Second, why do you want to multiply iron concentration by final volume?

If you take 1 mL of 1M solution and dilute it to 1L - how much substance do you have? 0.001x1 or 1x1?

where is the 1mL from?

[Borek]

where is the 1mL from?

Which one? In my question about about dilution? Out of the top of my head. In the sum 4+5+1? From the experiment dscription.

These are completely unrelated, but if you will try to understand what I asked about you should understood why your calculation of initial iron amount doesn't make sense.

[terry33199]

where is the 1mL from?

Which one? In my question about about dilution? Out of the top of my head. In the sum 4+5+1? From the experiment dscription.

These are completely unrelated, but if you will try to understand what I asked about you should understood why your calculation of initial iron amount doesn't make sense.

The 1mL from your question about dilution.  i'm still confused

[terry33199]

That kind of showed up wrong.  I'll try again:

(Fe^3+) + (SCN^-)  <->  FeSCN^2+

5ml of .002M FE(NO)_3 , 4ml of .002M KSCN, and 1 ml of water are mixed.  the equilibrium constant of FeSCN^2+ is .000131M
How many moles of Fe^3+ and SCN^- are initially present?
How many moles of FeSCN^2+ are in the mixture at equilibrium?
How many moles of Fe^3+ and SCN^- are used up in making FeSCN^2+?

is this right so far:
(a)
.002M x .005L = 1x10^-5 mol for Fe
and
.002M x .004L = 8x10^-6 mol for SCN

(b).000131M x .010L = 1.31x10^-6 mole FeSCN

[Borek]

is this right so far:
(a)
.002M x .005L = 1x10^-5 mol for Fe
and
.002M x .004L = 8x10^-6 mol for SCN

Now thats OK. Before you have used total volume instead of the volume of the reactant mixed.

000131M x .010L = 1.31x10^-6 mole FeSCN

Equilibrium constant is not an equilibrium concentration, these are different things.

Do you know how what the reaction quotient is? Do you now how the formula for equilibrium constant looks alike? If not - check them in your textbook, or in wikipedia.

[terry33199]

is this right so far:
(a)
.002M x .005L = 1x10^-5 mol for Fe
and
.002M x .004L = 8x10^-6 mol for SCN

Now thats OK. Before you have used total volume instead of the volume of the reactant mixed.

000131M x .010L = 1.31x10^-6 mole FeSCN

Equilibrium constant is not an equilibrium concentration, these are different things.

Do you know how what the reaction quotient is? Do you now how the formula for equilibrium constant looks alike? If not - check them in your textbook, or in wikipedia.

Is that the correct moles of FeSCN in the mixture at equilibrium?

[Borek]

No. You have to write formula for reaction equilibrium and solve it using ICE table Ygg mentioned.