Monique A. Gray
Experiment 3
Quantitative Analysis
Experiment 3: Analysis of a mixture of Carbonate and Bicarbonate
Introduction
The objective of this experiment is to introduce students to various titration techniques for quantitatively
determining the amount of a unknown sample, which in this case is carbonate and bicarbonate. Also, students will
be introduced to the concept of a standard in a titration and how its role in a titration for determining the amount
of an unknown is very important. Lastly, student will be learning to determine the amount of an unknown by
performing an indirect titration.
Procedure
Standardizing Acid and Base
-
Obtain an unknown that contains a mixture of carbonates and store in your dessicator.
Standard your base by preparing approximately 0.1M HCl and approximately 0.1M NaOH (1 Liter and
500mL respectively.
Accurately weight enough KHP to require 25mL of titrate. (Calculation to be done).
Repeat three trials of the same protocol.
Repeat the whole protocol to standardize your acid.
Experiment
-
-
-
Accurately weight 2.0-2.5g of unknown into a 25mL volumetric flask. Dilute to the mark with degassed
distilled water.
Pipet a 25mL aliquot of unknown into a 250mL Erlenmeyer flask and titrate with standardized HCl using
bromocresol green to determine the endpoint. Repeat three times. (Obtain an extra sample for a down
and dirty sample.)
Pipet a 25mL of unknown and a 50mL of standard NaOH into a 250mL Erlenmeyer and add 10mL of 10%
wt BaCl2, swirl to precipitate all BaCO3, then immediately titrate with HCl standard HCl using phenothalein
indicator. Repeat for three trials.
Repeat relative % carbonate and bicarbonate in your unknown with appreciate standardized deviation.
Calculations
Enough KHP for Titrant
g KHP = 0.1M
1 mole KHP 204.2212g
= 0.510553
0.025L
1mol KHP
Preparing NaOH
0.1M NaOH
1 mol 39.971g
= 1.99855g
0.5L 1 mol NaOH
Preparing HCl

Have to dilute it down from 6M to 0.1M
(6𝑀)(𝑥𝐿) = (0.1𝑀)(1𝐿) = 0.016666667 𝑥 1000 = 16.666 𝑚𝐿
Monique A. Gray
Experiment 3
Standardizing NaOH
KHP g 1 mol KHP
1 mol NaOH 39.971g NaOH 1 mol NaOH
1 204.2212g KHP 1mol KHP
1 mol NaOH 39.971g NaOH
0.5152g KHP
1 mol
1
204.2212g KHP
1 mol NaOH 39.971g NaOH 1 mol NaOH
1 mol KHP
1 mol NaOH 39.971g NaOH
Molarity =
M=
moles
liters
0.00252 mol NaOH
= 0.09615M
0.02621 L
Moles of Acid = Moles of Base
M1V1 = M2V2
(0.09628M) (0.02L) = ( ? ) (0.01953L ) =Macid 0.09859
Unknown C = 2.1060g
Moles of Carbonate
Molarity of HCl x mL HCl added (bromocresol titration) x 1/ 1000mL = moles of carbonates
0.09901 M HCl x 30.61mL x 1/1000mL = 0.00303 mol carbonates
Initial Moles of NaOH
Molarity of NaOH x Volume of NaOH initially = moles NaOH
0.09628 M NaOH x 0.05mL = 0.004814 moles NaOH initially
Moles NaOH Excess Reacted With HCl (phenolphthalein titration)
Molarity of HCl x mL HCl (phenol.) x 1/1000mL x 1mol NaOH/1 mol HCl
0.009901M HCl x 28.75 mL x 1/1000mL x1mol NaOH/1 mol HCl = 0.002846
NaOH Moles Reacted w/ HCO3Mol NaOH of initial – mol NaOH reacted in excess reacted = moles reacted with
0.004807mol NaOH – 0.002846 mol NaOH = 0.001961 mol reacted
Moles Bicarbonate
Moles carbonates – bicarbonates moles = moles carbonates
0.00303 mol carbonates – 0.01961 = 0.001069 mol carbonate
Relative % Carbonate
Monique A. Gray
Experiment 3
Mol carbonate x 60.007g Carbonate/1 mol carbonate x 1/ 2.1069 x 100%
0.001069 mol carbonate x 60.007g Carbonate/1 mol carbonate x 1/ 2.1069 x 100% = 3.04%
Relative % Bicarbonate
Mol carbonate x 61.007g bicarbonate/1 mol carbonate x 1/ 2.1069 x 100%
0.001961x 60.007g Carbonate/1 mol carbonate x 1/ 2.1069 x 100% = 5.585%
Standard Deviation
∑(xi −x̅)2
√
n−1
=S
√
(0.0304 − 0.02776)2 + (0.0260 − 0.02776)2 + (0.0269 − 0.02776)2
3−1
= +/- 0.01264 Carbonate
√(0.05585 − 0.05692)2 + (0.05573 − 0.05692)2 + (0.05653 − 0.05692)2
3−1
= +/- 0.0082 Bicarbonate
Trial 1#
Trial 2#
Trial 3#
KHP (g)
NaOH (mL)
0.5151g
0.5152g
0.5181g
26.21mL
26.24mL
26.28mL
Molarity of
NaOH (M)
0.09615
0.09614
0.09654
Volume of
HCl (mL)
19.53mL
19.29mL
19.52mL
NaOH Added
20mL
20mL
20mL
Trial #
mL HCl (Bromocresol)
mL HCl (phenolphthalein)
Trial 1#
Trial 2#
Trial 3#
30.61 mL
29.02 mL
29.62 mL
28.75 mL
28.79 mL
28.70 mL
Trial #
Trial 1#
Trial 2#
Trial 3#
Trial #
Trial 1 #
Trial 2 #
Trial 3 #
mL HCl (Bromocresol)
30.61 mL
29.02 mL
29.62 mL
Wt%
5.853%
5.573%
5.653%
mL HCl (phenolpthalien)
28.75 mL
28.79 mL
28.70 mL
Wt%
3.04%
2.60%
2.69%
Molarity Of
HCl (M)
0.09859
0.09982
0.09862
Moles Carbonates
(CO32- & HCO3-)
0.003030 mol
0.003873 mol
0.002930 mol
Moles of Carbonates
0.003030 mol
0.002873 mol
0.002930 mol
Ratio
80:20
80:20
80:20
Monique A. Gray
Experiment 3
Conclusion
In conclusion with some number crunching I found that the ratio of bicarbonate to carbonate was a 80:20 for
unknown C.
Post Lab Question
A primary standard is a reagent that contains no impurities and is stable to use in an experiment/ titration after it’s
weighted. Because of the uniqueness of primary standards they can be used to calibrate instruments.
A secondary standard in titrations is a standard that is standardized against a primary standard and used in the
experiement.
An indirect titration is a tititration technique used to find the concentration of a unknown substance by a series of
different titrations
A titrant is the solution in the buret that is being titrated into the analyte.