Dr Prem D Sattsangi Copyright 2009 1 Molar Absorptivity Define Molar Absorptivity Calculate the molar absorptivity with the following data 125 x 10 4 M solution has 045 OD absorbance at the ID: 199210
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Slide1
Q Acid-Base Indicators: Spectrophotometric Methods
Dr. Prem D. Sattsangi
Copyright © 2009Slide2
1. Molar Absorptivity
Define Molar Absorptivity
Calculate the molar absorptivity with the following data
1.25 x 10
-4
M solution has 0.45 O.D. absorbance at the
λ
max
(455 nm).
If the molar absorptivity of a compound is 33,350, calculate the absorbance of a 6.5 x 10
-5
M solution.Slide3
2. Moles
Calculate moles of NaOAc present in 5.00 mL of a 0.154 M soln.
n = M x VSlide4
3.
Calculate the [H
3
O
+
] for a buffer solution containing 0.00555 M AcO
-
(= NaOAc) and 0.00333 M AcOH. (Given K
a
for AcOH = 1.75 x 10
-5
)Slide5
4.
Given the following data, calculate the Ka for a weak acid.
K
a
=
[H
3
O
+
] [B
-
]
[HB]
[H
3
O
+
] = 3.45 x 10
-5
M, [B
-
] = 0.0045M, [HB] = 0.01 MSlide6
5.
For a buffer, pH = pK
a
+ log
[X
-
]
[HX]
At what concentration of [X
-
] and [HX] would pH = pK
a
?Slide7
6.
During a titration experiment we take 25.00 mL of AcOH and add 25 mL of water to make it 50 mL. If the first pH reading is 2.45, (Given: pH = -log [H
3
O
+
])
What is the [H
3
O
+
] of the diluted solution?
What would be the [H
3
O
+
] of the solution before dilution? Equation for dilution must be used V
1
x M
1
= V
2
x M
2
Calculate the K
a
of acetic acid using this data.
AcOH + H
2
O
↔
H
3
O
+
+ AcO
-
(Given: [AcOH] = 0.115 M)
K
a
=
[H
3
O
+
] [AcO
-
]
[AcOH]Slide8
7.
If the molarity of NaOH is 0.113 M, and it takes 7.5 mL of phosphoric acid, calculate the molarity of phosphoric acid using the following data on its titration.
H
3
PO
4
+ NaOH
NaH
2
PO
4
+ H-OH …Eq. 6
NaOH (0.113 M), 7.5 mL
H
3
PO
4
(? M), 25.00 mL
At what volume would you expect the 3
rd
equivalence point?
Molarity of H
3
PO
4
: [M = n/V*L]Slide9
8.
H
3
PO
4
can ionize in 3 steps. Write chemical equations for ionization steps 1 and 2.
Write expression for
K
a2
=Slide10
9.
Write an expression for K
sp
of Ag
2
SO
4
.Slide11
10.
KHT(s) is saturated in distilled water. The saturated solution (25.00 mL) required 16.5 mL of 0.0402 M NaOH to reach the end point.
Write an equation for this titration.
Calculate the solubility of KHT in distilled water. _______M
Calculate K
sp
for KHT [=________ (Unit _____)]Slide12
11.
An U.K. solution was given in 100 mL volumetric. After making it up to the mark, it was saturated with KHT, filtered and titrated. If 25.00 mL of the filtrate took 4.50 mL of 0.0402 M NaOH, calculate the molarity of the unknown. [K
sp
for KHT = 5.1 x 10
-4
M
2
]Slide13
12.
In a titration of solubility of KHT in 0.125 M KNO
3
, one used 4.53 mL of 0.0402 M NaOH solution for 25.00 mL of the saturated filtrate.
Calculate the solubility of KHT in 0.125 M KNO
3
. (=_____M)
K
sp
for KHT in presence of 0.125 M KNO
3
.Slide14
Molar Absorbtivity ”ε
”
ε
=
Absorbance
Concentration(M)
Calculate the molar absorptivity “
ε
” for morphine, if a 3.68 x 10
-3
M solution has a 0.45 O.D. absorbance at the
גּ
max
(328nm)Slide15
Calculating Moles of a Solution
n = M x V
n = number of moles of solution
M = molarity of the solution
V = volume of the solution in liters (L)
Calculate moles of NaOAc (sodium acatate) present in 5.00mL of a 0.250M solution.Slide16
Calculation of Hydrogen Ion Concentration
[H
3
O
+
] =
Ka x
[AcOH]
[AcO-]
Calculate the [H
3
O
+
] for a buffer solution containing 4.25 x 10
-3
M AcO
-
(acetate ion) and 2.25 x 10
-3
AcOH (acetic acid).
[Ka for AcOH = 1.75 x 10
-5
]Slide17
Bromocresol Green Indicator