What is the standard concentration of FeSCN^2+ if 18mL of 0.200M Fe(NO3)3 were combined with 2mL of 0.0020M KSCN?
KSCN + Fe^3+ ==> FeSCN^2+
KSCN = 0.2 x 18/20 = 0.18 M
Fe^3+ = 0.002 x 2/20 = 0.0002 M
So FeSCN^2+ must be 0.0002 M
You can make an ICE chart for that if you wish to see it better.
......KSCN + Fe^3+ ==> FeSCN^2+
I.....0.18...............0
add........0.0002............
C.-0.0002..-0.0002.....0.0002
E....about 0.18..0.....0.0002
To find the standard concentration of FeSCN^2+, we need to use the concept of stoichiometry and the given information.
First, we can start by writing the balanced chemical equation for the reaction between Fe(NO3)3 and KSCN:
Fe(NO3)3 + 3KSCN → Fe(SCN)3 + 3KNO3
Based on the equation, we can see that the ratio of moles of Fe(NO3)3 to moles of Fe(SCN)3 is 1:1. This means that if we know the concentration of Fe(NO3)3, we can directly determine the concentration of Fe(SCN)3.
Given that the volume of Fe(NO3)3 solution is 18 mL and the concentration is 0.200 M, we can convert the volume to liters by dividing by 1000:
Volume of Fe(NO3)3 solution = 18 mL = 18/1000 L = 0.018 L
Using the equation C = (moles of solute) / (volume of solution), we can calculate the moles of Fe(NO3)3:
moles of Fe(NO3)3 = (concentration of Fe(NO3)3) * (volume of Fe(NO3)3 solution)
= 0.200 M * 0.018 L
= 0.0036 moles
Since Fe(SCN)3 and Fe(NO3)3 have a 1:1 molar ratio, the moles of Fe(SCN)3 are also 0.0036 moles.
Now, let's focus on the KSCN solution. The volume of KSCN solution is 2 mL, which is equivalent to 2/1000 L = 0.002 L. The concentration of KSCN is given as 0.0020 M. Using the same formula, we can calculate the moles of KSCN:
moles of KSCN = (concentration of KSCN) * (volume of KSCN solution)
= 0.0020 M * 0.002 L
= 0.000004 moles
Next, we compare the moles of KSCN and Fe(SCN)3. Since Fe(SCN)3 and KSCN have a 1:3 molar ratio, we need to multiply the moles of KSCN by 3:
moles of Fe(SCN)3 = (moles of KSCN) * (3)
= 0.000004 moles * 3
= 0.000012 moles
Finally, we can calculate the standard concentration of FeSCN^2+ (Fe(SCN)2+) by dividing the moles of Fe(SCN)3 by the volume of the solution:
Standard concentration of FeSCN^2+ = (moles of Fe(SCN)3) / (total volume of solution)
= 0.000012 moles / (0.018 L + 0.002 L)
= 0.000012 moles / 0.02 L
= 0.0006 M
Therefore, the standard concentration of FeSCN^2+ is 0.0006 M.