Question

a.If a solution of a compound that has a molar absorptivity 45 M–1 cm–1 placed in a cuvette with a path length of 10 mm has an absorbance of 0.65, what is the molarity of the compound in solution? Show work.

b. What would the value of the equilibrium constant be for the formation of FeNCS2+ from Fe3+ and SCN– , if the final equilibrium concentration of [FeNCS2+] = 7.84 x 10–3 M when the solution initially had [Fe3+] = 1.5 x 10–3 M and [SCN– ] = 7.5 x 10–3 M?

c. Calculate the final [FeSCN2+] concentrations in flasks 1–6 from the Preparations of Calibration Curve procedure. Show work.

Answer #1

a. The providing data in the question are as follow:-

Molar absorptivity ()
of a compound = 45 M^{-1}cm^{-1}

Path length (l) of a cuvette = 10 mm

= 1 cm [1 mm = 0.1 cm]

Absorbance (A) = 0.65

We need to find out the value of molarity (C) or concentration of the compound in solution -

We remember the formula,

A = cl

c = A / l

c = 0.65 / 45 M^{-1}cm^{-1}* 1cm

c = 0.0145 M

So, Molarity of the compound in solution = 0.0145 M

1. A student mixes 5.00 mL 2.00 x 10-3 M Fe(NO3) in 1 M HNO3
with 3.00 mL 2.00 x 10-3 M KSCN and 2.00 mL of water. She finds
that in the equilibrium mixture the concentration of FeSCN2+ is 7.0
x 10-5 M. Find Kc for the reaction Fe3+ (aq0 + SCN- (aq0
------Fe(SCN)2+ (aq).
Step 1 Find the number of moles Fe3+ and SCN- initially
present.
Step 2. How many moles of FeSCN2+ are in the mixture at...

A student prepared the following two mixtures and recorded their
absorbances in a cuvette with a 1.00 cm path length:
Mix #
.20 M Fe3
.020 M Fe3
3.25*10^-4M SCN
Absorbance
1
10.0 mL
--
10.0 mL
.708
2
--
10.0 mL
10.0 mL
.423
1. Write the balanced equilibrium reaction of Fe3 (aq) with SCN
(aq) to form [FeSCN]2 (aq).
2. Write the equilibrium formation constant equation for the
reaction (Kf expression).
Determination of moral absoptivity
3. Assuming that...

1) If the absorbance of solution 1 at equilibrium is 0.23 and
the absorbance of the standard solution is 1.23, and the
concentration of FeSCN2+ in the standard solution is 1.00 M, what
is the equilibrium concentration of FeSCN2+ in solution 1? (Show
your work, 3 sig figs, and correct units)
2) If the initial concentration of Fe3+ in solution 1 was 0.25
M, what is the equilibrium concentration of Fe3+ that remains?
(Show your work, 3 sig figs, and...

Consider the following reaction: Fe3+(aq)+SCN−(aq)⇌FeSCN2+(aq) A
solution is made containing an initial [Fe3+] of 1.0×10^−3 M and an
initial [SCN−] of 7.8×10^−4 M . At equilibrium, [FeSCN2+]=
1.7×10^−4 M .
Part A Calculate the value of the equilibrium constant (Kc).
Express your answer using two significant figures. Kc =

2.) FeSCN2+ equilibrium concentration was found to be 3.20 x
10-5 M in a solution made by mixing 5.00 mL of 1.00 x 10-3 M
Fe(NO3)3 with 5.00 mL of 1.00 x 10-3 M HSCN. The H+ concentration
is maintained at 0.500 M at all times since the HSCN and Fe3+
solutions were prepared using 0.500 M HNO3 in place of distilled
water. a. How many moles FeSCN2+ are present at equilibrium? b. How
many moles each of Fe3+ and...

1) A student mixes 5.00 mL of 2.00 x 10-3 M Fe(NO3)3 with 5.00
mL of 2.00 x 10-3 M KSCN. She finds that in the equilibrium mixture
the concentration of FeSCN2+ is 1.40 x 10-4 M
a) What is the initial concentration in solution of the Fe3+ and
SCN- ?
b) What is the equilibrium constant for the reaction?
2. Assume that the reaction studied is actually: Fe3+ (aq) + 2
SCN- (aq) ↔ Fe(SCN)2+ (aq)
a) What is...

Solution
Volume of 0.20 M Fe3+
Volume of 0.002 M SCN-
Volume of H2O
A-1
25.0 mL
0.0 mL
75.0 mL
A-2
25.0 mL
5.0 mL
70 mL
A-3
25.0 mL
7.0 mL
68.0 mL
A-4
25.0 mL
9.0 mL
66.0 mL
A-5
25.0 mL
11.0 mL
64.0 mL
Solution
Volume of 0.002 M Fe3+
Volume of 0.002 M SCN-
Volume of H2O
B-1
5.0 mL
1.0 mL
5.0 mL
B-2
5.0 mL
2.0 mL
4.0 mL
B-3
5.0 mL...

From her Beer's Law plot in part A, a student obtained a best
fit line of y=4.11 x 103x + 0.00 For part B, she made up a series
of solutions. One solution had the following composition and
absorbance: Vol 2.00 x 10-3 M Fe(NO3)3 (mL)= 5.00 Vol of 2.00 x
10-3 M KSCN (mL)= 5.00 Vol of 0.5 M HNO3 (mL)= 0.00 Absorbance at
450 nm= 0.629 What is the initial concentration of Fe(NO3)3 in the
solution (after mixing...

The molar absorptivity of a dye is ε = 3.3 /M cm; what is the
concentration of the solution (C) if the path length is given as ℓ
= 1 cm and the absorption is A = 0.72? Beer-Lambert Law: A = εℓC
SHOW WORK
(a) 0.33 M
(b) 1.4 M
(c) 0.22 M
(d) 0.72 M

A 0.26 M solution of compound "B" is measured in a 1.00 cm path
length cuvette at a wavelength of 565 nm. The percentage of light
transmitted through the cell is 44%. What is the molar absorbance
of this sample at 565 nm (in units of mol-1 cm-1)?

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