Analysis of Bottled Water

 

IV. Bicarbonate – Form D

 

The measure of the presence of bicarbonate is referred to as alkalinity.  High alkalinity levels (above 500 mg/l) are usually associated with high pH values, hardness and high dissolved solids and have adverse effects on plumbing systems, especially on hot water systems (water heaters, boilers, heat exchangers, etc.).  Water with low alkalinity levels (less than 75 mg/l), especially some surface waters and rainfall, are subject to changes in pH due to dissolved gasses that may be corrosive to metallic fittings.  The recommended range of bicarbonates in drinking water is 30 to 400 ppm.

Sources:

http://www.aqualink.com/columns/k-love3.html

http://www.idph.state.il.us/envhealth/pdf/DrinkingWater.pdf

 

HCO3- (aq) + HCl (aq) → H2O + CO2 (g) + Cl- (aq)

 

Procedure:

 

·        Place 20 drops of water sample in a watch glass

·        Add one drop of methyl orange indicator

o       Stir with toothpick (The solution should be yellow)

·        Titrate with 0.02M HCl one drop at a time

o       Stir with toothpick after each drop

o       Keep track of the number of drops added

o       Stop at the first color change from yellow to orange

·        Record the number of drops of HCl added

·        Repeat procedure four more times - maintain precision within one drop

·        Calculate the amount of Bicarbonate and record your data below

·        Transfer all your data to the class data sheet - Form F

 

Water Samples 

Sample 1:

#1

#2

#3

#4

#5

Average

# of Drops of water

20

20

20

20

20

HCl drops

Drops of HCl

 

 

 

 

 

 

 

Sample 2:

#1

#2

#3

#4

#5

Average

# of Drops of water

20

20

20

20

20

HCl drops

Drops of HCl

 

 

 

 

 

 

 

Sample 3:

#1

#2

#3

#4

#5

Average

# of Drops of water

20

20

20

20

20

HCl drops

Drops of HCl

 

 

 

 

 

 

 

Sample 4:

#1

#2

#3

#4

#5

Average

# of Drops of water

20

20

20

20

20

HCl drops

Drops of HCl

 

 

 

 

 

 

 

ppm of Bicarbonate = [(0.02M HCl)(Av. drops of HCl)(61,000 mg/moles)] ÷

                                                (Av. drops of water sample)

 

Bicarbonate Data

Type and Brand of water

Bicarbonate (ppm)

 

 

 

 

 

 

 

 

 

 

 

 

Levels of Bicarbonate (ppm)

Less than 75

Low

75-350

Moderate

350-500

Moderately High

Above 500

High

 

Questions

 

  1. What is the ratio of bicarbonate concentration to the concentration of calcium and magnesium in the water samples?
  2. Is the bicarbonate level in each water sample within the recommended drinking water range (30 to 400 ppm)?
  3. Explain how the measure of the presence of bicarbonate in water is referred to as alkalinity.