CHEMISTRY 108
LABORATORY 8
ANALYSIS OF SOLUTIONS
Goals
Your team is called to compare two samples of bottled water by determining the pH,
water hardness and alkalinity.
Materials Needed
pH meters
Calibration buffer pH 7 and 4
25 mL pipets (enough for five groups. Each group will need 2 pipets)
50 mL burets
Buret holders and stands
Magnetic stirring bars
0.0100 M Sodium EDTA solution, standardized
pH 10 buffer (NH3/NH4+ buffer plus MgEDTA)
Calmagite indicator
0.0100 M HCl solution, standardized
Methyl orange indicator
Two bottled water samples (not purified or distilled water): enough for five groups
Control water sample (distilled water)
Introduction
Bottled water is not pure water. Since it comes from wells or springs, it often has a
relatively high mineral content. It has calcium and magnesium ions, the primary sources
of water hardness. It also contains bicarbonate ion, the primary sources for the alkalinity
or acid neutralizing capacity of the water. In addition, bottled water contains other
soluble ionic substances.
We can determine the total amount of Ca2+ and Mg2+ ions in water by titrating a water
sample with a standardized EDTA solution. EDTA forms strong 1:1 metal-EDTA
complex with Ca2+ and Mg2+ ions. The indicator used in the titration is Calmagite
indicator which is red/magenta in the presence of free Ca2+ and Mg2+ ions and blue in
their absence.
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Structure of EDTA (ethylene diamine tetraacetate)
Structure of Metal-EDTA complex
We commonly report water hardness as milligrams of CaCO3 per liter of water or ppm.
Therefore, we calculate the number of moles of EDTA used in titration and convert it to
the number of moles of Ca2+ and Mg2+ ions (it is a 1:1 reaction). Then it is converted to
milligrams of CaCO3.
Table I. Classification of water hardness (hardness as calcium carbonate).
Classification
mg/L or ppm
Soft
0 - 17.1
Slightly hard
17.1 - 60
Moderately hard 60 - 120
Hard
120 - 180
Very Hard
180 & over
Example: A student used 11.35 mL of 0.0100 M EDTA solution to titrate 25.00 mL of
the sample water. Report the hardness in milligrams of CaCO3 per liter of the sample (or
ppm). What is the classification of the water sample (soft, slightly hard, moderately hard,
etc.)?
moles of EDTA used = 0.0100 M  0.01135 L = 0.0001135 mol
moles of Ca2+ in 25 mL = moles of EDTA required = 0.0001135 mol
grams of CaCO3 in 25 mL= mol of Ca2+  molar mass of CaCO3 = 0.0001135 mol  100
g/mol = 0.01135 g
2
1000mL
= 0.454 g
25 mL
1000mg
mg of CaCO3 in 25 mL = 0.01135 g 
= 11.35 mg
1g
1000mL
mg of CaCO3 in 1 L = 11.35 mg 
= 454 mg CaCO3 in 1 L= 454 ppm
25 mL
According to the classification of water, this sample is very hard (over 180 ppm).
grams of CaCO3 in 1 L = 0.01135 g 
We can determine the amount of bicarbonate ions in water similarly by titrating a water
sample with a standardized HCl solution. The indicator used in the titration is methyl
orange indicator which changes color from yellow to red when an excess HCl is present
and the solution pH drops below 4. It is a 1:1 reaction.
HCO3- (aq) + HCl (aq) → H2O (l) + CO2 (g) + Cl- (aq)
Example: A student used 5.20 mL of 0.0100 M HCl solution to titrate 25.00 mL of the
sample water. Report the alkalinity in molar concentration of bicarbonate and milligrams
of bicarbonate per liter of the sample (ppm).
moles of HCl required = 0.0100 M  0.00520 L = 0.0000520 mole
moles of bicarbonate in 25 mL = moles of HCl required = 0.0000520 mole
molarity of bicarbonate = moles/L = 0.0000520 mole / 0.02500 L = 0.00208 M
milligrams of bicarbonate per L= mole of bicarbonate  molar mass of bicarbonate 
1000 mg/g = 0.00208 M  61.02 g/mole  1000 mg/g = 127 mg/L = 127 ppm
Experimental Procedure
Water Hardness Test: 25 mL of water sample is combined with 2 mL of NH3/NH4+ buffer
and five drops of calmagite indicator. EDTA out of the buret is added until the color
goes from red to blue. The volume of EDTA required is noted and the concentration of
CaCO3 is calculated. Use a 25 mL sample of distilled water as your control.
Alkalinity Test: 25 mL of water sample is combined with five drops of methyl orange
indicator. HCl out of the buret is added until the color goes from yellow to red. The
volume of HCl required is noted and the concentration of bicarbonate is calculated. Use
a 25 mL sample of distilled water as your control.
Safety Precautions
The fumes from the NH3/NH4Cl buffer at pH 10 are toxic, corrosive, and irritating.
Dispense under a fume hood. Wash hands thoroughly before leaving the lab.
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Pre Laboratory Questions
1. A student used 6.05 mL of 0.0100 M EDTA solution to titrate 25 mL of the
sample water. Report the hardness in milligrams of CaCO3 per liter of the
sample. What is the classification of the water sample (soft, slightly hard,
moderately hard, etc.)?
2. Is it better to drink hard water or soft water? Explain your answer.
3. Is acidic water or basic water better for our health? Explain your answer.
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REPORT SHEET
LABORATORY 8: ANALYSIS OF SOLUTIONS
Name:______________________________ Section:_____________ Date:__________
Partner:___________________________
Bottled water sample 1
Bottled water sample 2
Distilled water
Identification
_____________
_____________
_____________
pH
____________
____________
____________
Water Hardness
Bottled water sample 1
Volume of water sample titrated, mL
__________________
Trial#
Volume of EDTA required, mL
Number of moles of EDTA, mol
Number of moles of Ca2+, mol
Water hardness, mg CaCO3 in L sample
1
________
________
________
________
Average Total Hardness, mg CaCO3/L
________
Classification of your water sample
_______________
Bottled water sample 2
Volume of water sample titrated, mL
__________________
Trial#
Volume of EDTA required, mL
Number of moles of EDTA, mol
Number of moles of Ca2+, mol
Water hardness, mg CaCO3 in L sample
1
________
________
________
________
Average Total Hardness, mg CaCO3/L
________
Classification of your water sample
_______________
Distilled water
Volume of water sample titrated, mL
__________________
Trial#
Volume of EDTA required, mL
Number of moles of EDTA, mol
Number of moles of Ca2+, mol
Water hardness, mg CaCO3 in L sample
1
________
________
________
________
5
2
________
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________
________
2
________
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2
________
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________
________
Label
____________
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3
________
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3
________
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3
________
________
________
________
Average Total Hardness, mg CaCO3/L
________
Classification of your water sample
_______________
Alkalinity
Bottled water sample 1
Volume of water sample titrated, mL
__________________
Trial#
Volume of HCl required, mL
Number of moles of HCl, mol
Number of moles of bicarbonate, mol
alkalinity, mg bicarbonate in L sample
1
________
________
________
________
Average alkalinity, mg bicarbonate/L
________
Bottled water sample 2
Volume of water sample titrated, mL
__________________
Trial#
Volume of HCl required, mL
Number of moles of HCl, mol
Number of moles of bicarbonate, mol
alkalinity, mg bicarbonate in L sample
1
________
________
________
________
Average alkalinity, mg bicarbonate/L
________
Distilled water
Volume of water sample titrated, mL
__________________
Trial#
Volume of HCl required, mL
Number of moles of HCl, mol
Number of moles of bicarbonate, mol
alkalinity, mg bicarbonate in L sample
1
________
________
________
________
Average alkalinity, mg bicarbonate/L
________
2
________
________
________
________
2
________
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2
________
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3
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3
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3
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POST-LABORATORY PROBLEMS: Must be included in your lab report.
1.
The pH of water for human consumption should be close to neutral. How closely
do your samples compare with this goal?
2.
Report the water hardness in ppm and molar concentration of CaCO3. How
would you classify your water samples according to table 1?
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3.
Report the bicarbonate concentrations in ppm and molar concentration.
4.
Compare the water hardness and alkalinity of two water samples. Which one has
higher water hardness? Which one has higher alkalinity? Can you decide which
one is better?
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