Orlando 1
Quantitative Analytical Chemistry
Joseph Orlando
Lab #3: Analysis of a Mixture of Carbonate and Bicarbonate
Purpose:
The purpose of this experiment is to become familiar with not only titrations, but also of the concept of the use
of standards. In this experiment we will be determining the amount of two separate carbonate compounds by
using an indirect titration.
HCO3- + 2 H+ -----> H2CO3
CO32- + 2 H+ -----> H2CO3
HCO3- + OH- -----> CO32- + H2O
Ba2+ + CO32- -----> BaCO3
Ba3+ + 2 OH------> Ba(OH)2
Procedure:
1. Obtain unknown and store in desiccator until needed. Prepare 1 L of 0.1 M HCl and 500mL 0.1 M NaOH.
Weigh out enough primary standard grade KHP to require a minimum of 25mL titrant. Repeat this process
three times.
2. Weigh 2-2.5 grams unknown into a 250mL volumetric flask (2.075 grams of unknown used). Dilute to the
mark with boiled/cooled triply distilled H2O.
3. Pipet 25mL of unknown into a 250mL Erlenmeyer flask and titrate with standardized HCl using bromocresol
green to determine the endpoint. Repeat this process three times.
4. Pipet 25mL of unknown and 50mL standardized NaOH into a 250mL Erlenmeyer flask. Add 10mL of 10%
BaCl2, swirl to precipitate all BaCO3, immediately titrate with standardized HCl using phenolphthalein
indicator. Repeat this process three times.
Data:
NaOH Standardization
Amount (mL) of NaOH
titrated
24.85
Molarity (M) of NaOH
Trial #1
Amount (g) of KHP
Used
0.5107
Trial #2
0.5132
26.45
0.0943
Trial #3
0.5329
28.40
0.0920
Average
0.5189
26.56
0.0957
0.1008
Orlando 2
HCl Standardization
Amount (mL) of HCl
titrated
Molarity (M) of HCl
Trial #1
Amount (mL) of NaOH
used to determine HCl
molarity
10.0
9.95
0.0962
Trial #2
10.0
9.80
0.0976
Trial #3
10.0
9.70
0.0986
Average
10.0
9.82
0.0975
Unknown Titration
Molarity (M) of unknown sample
Trial #1
Amount (mL) HCl titrated into
unknown C sample
13.35
Trial #2
19.55
0.0762
Trial #3
20.40
0.0795
Average
17.77
0.0692
0.0521
BaCl2 Titration
Trial #1
Amount (mL) of
HCl titrated
26.73
Moles NaOH
(initial)
0.00475
Moles NaOH
(excess)
0.00261
Moles NaOH
reacted
0.00214
Trial #2
25.85
0.00475
0.00252
0.00223
Trial #3
25.60
0.00475
0.00122
0.00353
Average
26.06
0.00475
0.00212
0.00263
Moles Carbonate
Trial #1
Moles of
Bicarbonate
0.00214
Trial #2
0.00047
Relative %
Carbonate
1.36%
Relative %
Bicarbonate
6.29%
0.00223
0.00029
0.84%
6.56%
Trial #3
0.00353
0.00031
0.89%
10.38%
Average
0.00263
0.00036
1.03%
7.74%
Orlando 3
Equations:.
Mass (g) KHP Used in Step 1
0.025 𝐿 𝑡𝑖𝑡𝑟𝑎𝑛𝑡 ×
0.1 𝑚𝑜𝑙 𝑡𝑖𝑡𝑟𝑎𝑛𝑡
1 𝑚𝑜𝑙 𝐾𝐻𝑃
204.22 𝑔 𝐾𝐻𝑃
×
×
= 0.51 𝑔 𝐾𝐻𝑃
1 𝐿 𝑡𝑖𝑡𝑟𝑎𝑛𝑡
1 𝑚𝑜𝑙 𝑡𝑖𝑡𝑟𝑎𝑛𝑡
1 𝑚𝑜𝑙 𝐾𝐻𝑃
Moles NaOH (initial)
𝑀 𝑁𝑎𝑂𝐻 × 𝐿 𝑁𝑎𝑂𝐻 𝑢𝑠𝑒𝑑
Moles NaOH (excess)
𝑀 𝐻𝐶𝑙 × 𝐿 𝐻𝐶𝑙 𝑢𝑠𝑒𝑑
Moles NaOH reacted
𝑖𝑛𝑖𝑡𝑖𝑎𝑙 𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻 − 𝑒𝑥𝑐𝑒𝑠𝑠 𝑚𝑜𝑙𝑒𝑠 𝑁𝑎𝑂𝐻
Moles Bicarbonate
𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑁𝑎𝑂𝐻 𝑟𝑒𝑎𝑐𝑡𝑒𝑑 ×
1 𝑚𝑜𝑙𝑒 Bicarbonate
1 𝑚𝑜𝑙𝑒 𝑁𝑎𝑂𝐻
Moles Carbonate
𝑒𝑥𝑐𝑒𝑠𝑠 𝑚𝑜𝑙𝑒𝑠 𝑜𝑓 𝑁𝑎𝑂𝐻 − 𝑚𝑜𝑙𝑒𝑠 𝐵𝑖𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
Relative % Carbonate
𝑚𝑜𝑙𝑒𝑠 𝐶𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒 ×
60.007 𝑔 𝐶𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
1
×
× 100%
1 𝑚𝑜𝑙𝑒 𝐶𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
2.075 𝑔 𝑈𝑛𝑘𝑛𝑜𝑤𝑛 𝐶
Relative % Bicarbonate
𝑚𝑜𝑙𝑒𝑠 𝐵𝑖𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒 ×
61.014 𝑔 𝐵𝑖𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
1
×
× 100
1 𝑚𝑜𝑙𝑒 𝐵𝑖𝑐𝑎𝑟𝑏𝑜𝑛𝑎𝑡𝑒
2.075 𝑔 𝑈𝑛𝑘𝑛𝑜𝑤𝑛 𝐶
Conclusion:
In the titration to determine percent composition of carbonate and bicarbonate, it was calculated that the
sample contained an average of 1.03% carbonate and 7.74% bicarbonate. This titration was accomplished by
titrating standardized HCl (average molarity = 0.0975 M) into a solution of unknown and standardized NaOH
(average molarity = 0.0957 M). The data obtained is relatively persistent between the three trials with a low
calculated standard deviation.
Orlando 4
Post Lab Questions:
1. What is meant by a primary standard?
Primary standards are reagents which can be weighed easily and have a weight that is truly
representative of the number of moles of substance contained. Primary standards are used in titration
and are essential for determining an unknown concentration.
2. What is a secondary standard?
A secondary standard is a compound used in analysis after evaluation against primary standards.
3. What is an indirect titration?
An indirect titration is a two-step process.
1. Reactant X of unknown concentration is reacted with a reactant of known concentration (we
will call this reactant B).
2. A titration is then performed to determine the amount of reactant B in excess.
4. Define titrant.
A titrant is a solution of known concentration which is titrated into another solution to determine the
concentration of another chemical compound.