Hardness, Calcium DOC316.53.

01157

Titration Method with EDTA1, 2 Method 8222

0–25,000 mg/L as CaCO3 Buret Titration
Scope and application: For water, wastewater and seawater.
1 USEPA accepted when 0.020 N titrant is used.
2 Adapted from Standard Methods for the Examination of Water and Wastewater.

Test preparation

Before starting
Magnesium is not included in the results but must be in the sample for a sharp endpoint. If the sample does not contain
magnesium, add 1 to 2 drops of Magnesium Standard Solution, 10-g/L as CaCO3, to the sample before the test is started.
As an alternative to the CalVer 2 Calcium Indicator Powder Pillow, use a 0.1-g scoop of CalVer 2 Calcium Indicator Powder.
Review the Safety Data Sheets (MSDS/SDS) for the chemicals that are used. Use the recommended personal protective
equipment.
Dispose of reacted solutions according to local, state and federal regulations. Refer to the Safety Data Sheets for disposal
information for unused reagents. Refer to the environmental, health and safety staff for your facility and/or local regulatory
agencies for further disposal information.

Items to collect
Description Quantity

CalVer 2 Calcium Indicator Powder Pillow 1

Potassium Hydroxide Standard Solution, 8 N 1 mL
TitraVer Hardness Titrant (use a concentration that is applicable to the selected sample
varies
volume)
Buret, Class A, 25 mL 1
Graduated cylinder (use a size that is applicable to the selected sample volume), or TenSette
1
pipet with tips
Erlenmeyer flask, 250 mL 1
Funnel, micro 1
Support stand with buret clamp 1
Water, deionized varies

Refer to Consumables and replacement items on page 6 for order information.

Sample collection
• Collect samples in clean glass or plastic bottles that have been cleaned with a
detergent and rinsed with 1:1 nitric acid and deionized water.
• To preserve samples for later analysis, adjust the sample pH to 2 or less with
concentrated nitric acid (about 2 mL per liter). No acid addition is necessary if the
sample is tested immediately.
• Keep the preserved samples at room temperature for a maximum of 6 months.
• Before analysis, adjust the pH to 7 with Potassium Hydroxide Standard Solution.
• Correct the test result for the dilution caused by the volume additions.

1
Test procedure

1. Select a sample volume 2. Fill a 25-mL buret to the 3. Use a graduated cylinder 4. Pour the sample into a
and titrant from Table 1 zero mark with the titrant. or a pipet1 to measure the clean, 250-mL Erlenmeyer
on page 3. sample volume from Table 1 flask.
on page 3.

5. If the sample volume is 6. Add 1 mL of 8 N 7. Swirl to mix. 8. Add the contents of one
less than 50 mL, dilute to Potassium Hydroxide CalVer 2 Calcium Indicator
approximately 50 mL with Standard Solution. Powder Pillow.
deionized water.

9. Swirl to mix. 10. Put the flask under the 11. Use the multiplier in
buret. Swirl the flask. Add Table 1 on page 3 to
titrant until the color calculate the concentration.
changes from red to pure mL of titrant × multiplier =
blue. mg/L Ca as CaCO3.

Sample volumes and multipliers

Select a range in Table 1, then read across the table row to find the applicable
information for this test. Use the multiplier to calculate the concentration in the test
procedure.

1 Titration accuracy has a direct relation to the accuracy of the sample volume measurement. For smaller
volumes, it is recommended to use a pipet to increase accuracy.

2 Hardness, Calcium (25,000 mg/L)

 Example: A 50-mL sample was titrated with 0.020 N titrant and 12 mL of titrant was used
at the endpoint. The concentration is 12 mL × 20 = 240 mg/L Ca as CaCO3.
Table 1 Sample volumes and multipliers
Range (mg/L) Sample volume (mL) Titrant—TitraVer hardness Multiplier
0–500 50 0.020 N 20
400–1000 25 0.020 N 40
1000–2500 10 0.020 N 100
2000–5000 5 0.020 N 200
1000–5000 50 0.200 N 200
4000–10,000 25 0.200 N 400
10,000–25,000 10 0.200 N 1000

Conversions units
To change the units or chemical form of the test result, multiply the test result by the
factor in Table 2.
Table 2 Conversions
mg/L Ca as CaCO3 to... multiply by... Example
mg/L as Ca 0.40 1000 mg/L as CaCO3 x 0.40 = 400 mg/L Ca
German degrees hardness (Gdh) 0.056 1000 mg/L as CaCO3 × 0.056 = 56 Gdh
Grains per gallon (gpg) 0.058 1000 mg/L as CaCO3 x 0.058 = 58 gpg

Interferences

WARNING
Chemical hazard. Potassium cyanide is toxic. Make sure to add potassium cyanide to the
sample after the 8 N Potassium Hydroxide Standard Solution has been added. Keep
cyanide solutions at more than pH 11 to prevent exposure to hydrogen cyanide gas.
Dispose of reacted solutions according to local, state and federal regulations.

An interfering substance can prevent the color change at the titration endpoint. A smaller
sample volume can often dilute the interfering substance to a level at which the
substance does not interfere. Table 3 shows the substances that can interfere with this
test.
Table 3 Interferences
Interfering substance Interference level
Acidity 10,000 mg/L acidity as CaCO3 does not interfere.
Alkalinity 10,000 mg/L alkalinity as CaCO3 does not interfere.
Aluminum Causes a slow endpoint. The sample can contain a maximum of 200 mg/L aluminum if sufficient
time is given for the color change.
Barium Barium is titrated at the same time with calcium and interferes with this test, but it is unusual to find
high levels of Barium in natural waters.
Chloride The chloride level in seawater does not interfere. Solutions that are saturated with chloride do not
show a sharp endpoint.
Cobalt Interferes directly. Add 0.5 grams of potassium cyanide after the 8 N Potassium Hydroxide
Standard Solution during the test procedure to remove the interference from a maximum of
20 mg/L cobalt.

Hardness, Calcium (25,000 mg/L) 3

 Table 3 Interferences (continued)
Interfering substance Interference level
Copper Interferes at 0.1 mg/L copper. Add 0.5 grams of potassium cyanide after the 8 N Potassium
Hydroxide Standard Solution during the test procedure to remove the interference from a
maximum of 100 mg/L copper.
Iron More than 8 mg/L iron causes an orange-red to green endpoint. Results are accurate to 20 mg/L
iron with this endpoint.
Magnesium The formation of magnesium hydroxide at the high test pH prevents interference from 200 mg/L
magnesium. Samples with more than 200 mg/L magnesium do not give a distinct endpoint.
Manganese Interferes at more than 5 mg/L manganese.
Nickel Interferes at 0.5 mg/L nickel. Add 0.5 grams of potassium cyanide after the 8 N Potassium
Hydroxide Standard Solution during the test procedure to remove the interference from a
maximum of 200 mg/L nickel.
Orthophosphate Forms calcium phosphate and causes a slow endpoint. If sufficient time is given to let the calcium
phosphate dissolve during the titration, the orthophosphate will not interfere with the test.
Polyphosphates Interfere directly and are included in the test result.
Strontium Strontium is titrated at the same time with calcium and interferes with this test, but it is unusual to
find high levels of Strontium in natural waters.
Temperature Samples at 20 °C (68 °F) or colder should be titrated slowly near the endpoint to give sufficient
time for the color change.
Zinc Interferes at 5 mg/L zinc. Add 0.5 grams of potassium cyanide after the 8 N Potassium Hydroxide
Standard Solution during the test procedure to remove the interference from a maximum of
100 mg/L zinc.
Highly buffered samples Can prevent the correct pH adjustment (of the sample) by the reagents. Sample pretreatment may
or extreme sample pH be necessary.

Accuracy check
Standard additions method (sample spike)—0.020 N titrant
Use the standard additions method to validate the test procedure, reagents, apparatus,
technique and to find if there is an interference in the sample.
Items to collect:
• Calcium Hardness Standard Solution, 10,000 mg/L as CaCO3, 10-mL Voluette
ampule
• Ampule Breaker
• Pipet, TenSette, 0.1–1.0 mL and pipet tips

1. Use the test procedure to measure the concentration of the standard solution. Use
the 0.020 N titrant.
2. Use a TenSette pipet to add 0.1 mL of the standard solution to the titrated sample.
3. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
4. Add one more 0.1-mL addition of the standard solution to the titrated sample.
5. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
6. Add one more 0.1-mL addition of the standard solution to the titrated sample.
7. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
8. Compare the actual result to the correct result. The correct result for this titration is
1.0 mL of titrant for each 0.1-mL addition of the standard solution. If much more or
less titrant was used, there can be a problem with user technique, reagents,
apparatus or an interference.

4 Hardness, Calcium (25,000 mg/L)

Standard additions method (sample spike)—0.200 N titrant
Use the standard additions method to validate the test procedure, reagents, apparatus,
technique and to find if there is an interference in the sample.
Items to collect:
• Calcium Hardness Standard Solution, 10,000 mg/L as CaCO3, 10-mL Voluette
ampule
• Ampule Breaker
• Pipet, TenSette, 0.1–1.0 mL and pipet tips

1. Use the test procedure to measure the concentration of the standard solution. Use
the 0.200 N titrant.
2. Use a TenSette pipet to add 1.0 mL of the standard solution to the titrated sample.
3. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
4. Add one more 1.0-mL addition of the standard solution to the titrated sample.
5. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
6. Add one more 1.0-mL addition of the standard solution to the titrated sample.
7. Titrate the spiked sample to the endpoint. Record the mL of titrant added.
8. Compare the actual result to the correct result. The correct result for this titration is
1.0 mL of titrant for each 1.0-mL addition of the standard solution. If much more or
less titrant was used, there can be a problem with user technique, reagents,
apparatus or an interference.

Standard solution method—0.020 N titrant

Use the standard solution method to validate the test procedure, reagents, apparatus and
technique.
Items to collect:
• Calcium Chloride Standard Solution, 1000 mg/L as CaCO3
• Pipet, TenSette, 1.0–10.0 mL and pipet tips

1. Use the test procedure to measure the concentration of the standard solution. Use
25.0 mL of the standard solution and the 0.020 N titrant.
2. Compare the actual result to the correct result. The correct result for this titration is
25 mL of titrant.

Standard solution method—0.200 N titrant

Use the standard solution method to validate the test procedure, reagents, apparatus and
technique.
Items to collect:
• Calcium Hardness Standard Solution, 10,000 mg/L as CaCO3, 10-mL Voluette
ampule
• Ampule Breaker
• Pipet, TenSette, 1.0–10.0 mL and pipet tips

1. Use the test procedure to measure the concentration of the standard solution. Use
10.0 mL of the standard solution and the 0.200 N titrant.
2. Compare the actual result to the correct result. The correct result for this titration is
10 mL of titrant.

Summary of method
Potassium hydroxide is added to the sample to adjust the pH to 12 to 13, which causes a
magnesium hydroxide precipitate to form. CalVer 2 Calcium Indicator is then added,
which reacts with calcium to give a red color. The EDTA titrant is added, which reacts
with all the free calcium. After the EDTA has reacted with all of the free calcium ions, the

Hardness, Calcium (25,000 mg/L) 5

 EDTA removes the calcium from the indicator. The indicator color then changes from red
to blue.
Consumables and replacement items
Required reagents

Description Quantity/Test Unit Item no.

Hardness (Calcium) Reagent Set (approximately 100 tests): — each 2447000

CalVer 2 Calcium Indicator Powder Pillows 1 pillow 100/pkg 85299
Potassium Hydroxide Standard Solution, 8 N 1 mL 100 mL MDB 28232H
®
TitraVer Hardness Titrant, 0.020 N varies 1L 20553
®
TitraVer Hardness Titrant, 0.200 N varies 500 mL 102149

Required apparatus

Description Quantity/test Unit Item no.

Buret clamp, double 1 each 32800

Buret, Class A, 25 mL 1 each 2636540
Support stand 1 each 56300
Funnel, micro 1 each 2584335
Graduated cylinders—Select one or more for the sample volume:
Cylinder, graduated, 5 mL 1 each 50837
Cylinder, graduated, 10 mL 1 each 50838
Cylinder, graduated, 25 mL 1 each 50840
Cylinder, graduated, 50 mL 1 each 50841
Cylinder, graduated, 100 mL 1 each 50842
®
Tensette pipets and pipet tips—Select one or more for the sample volume:
®
Pipet, TenSette , 0.1–1.0 mL 1 each 1970001
®
Pipet tips, TenSette Pipet, 0.1–1.0 mL varies 50/pkg 2185696
®
Pipet, TenSette , 1.0–10.0 mL 1 each 1970010
®
Pipet tips, TenSette Pipet, 1.0–10.0 mL varies 50/pkg 2199796
Flask, Erlenmeyer, 250 mL 1 each 50546

Recommended standards

Description Unit Item no.

Calcium Chloride Standard Solution, 1000 mg/L as CaCO3 1L 12153

Calcium Hardness Standard Solution, 10,000 mg/L as CaCO3, 10-mL Voluette ampule 16/pkg 218710

Optional reagents and apparatus

Description Unit Item no.

®
Ampule Breaker, 10-mL Voluette Ampules each 2196800
Bottle, sampling, with cap, low density polyethylene, 250 mL 12/pkg 2087076
CalVer® 2 Calcium Indicator Powder 113 g 28114H
Magnesium Standard Solution, 10-g/L as CaCO3 29 mL 102233

6 Hardness, Calcium (25,000 mg/L)

Optional reagents and apparatus (continued)
Description Unit Item no.

Nitric Acid, concentrated 500 mL 15249

Nitric Acid Solution, 1:1 500 mL 254049
Potassium Cyanide, ACS 100 g 76714
Potassium Hydroxide Standard Solution, 8 N 500 mL 28249
Spoon, measuring, 0.1 g each 51100
Stir bar, octagonal each 2095352
TitraStir® Titration Stand, 115 VAC each 1940000
TitraStir® Titration Stand, 230 VAC each 1940010

Hardness, Calcium (25,000 mg/L) 7

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