This document describes a procedure for determining the total hardness of water samples. Hard water contains high amounts of calcium and magnesium ions that can precipitate out of solution and cause problems. Measuring hardness is important for water treatment processes. The procedure involves titrating water samples with EDTA solution using Eriochrome Black-T indicator. The endpoint is identified by a color change from wine red to blue. By comparing titrations of the original sample and one that is boiled, the procedure determines total hardness. Accurate measurement of hardness is necessary to optimize water softening treatments.
2. Contents
• What is Hardness
• Why determine Hardness
• Determination of Hardness
• Procedure
• Observation
• Reference
3. What is Hardness
• Hard water contains high amounts of minerals in the form of ions,
especially the metals calcium and magnesium, which can precipitate out
and cause problems in water conducting or storing vessels like pipes.
• The most common ions found in hard water are the metal cations calcium
(Ca2+) and magnesium (Mg2+), though iron, aluminum, and manganese
may also be found in certain areas. These metals are water soluble,
meaning they will dissolve in water.
• The ions can precipitate out of the solution. This displacement of minerals
from the solution is responsible for the calcination often seen on water
faucets, which is a precipitation of calcium or magnesium carbonate.
4. Why Measure Hardness?
• In general, hard water forms solid deposits comprised of mainly
calcium and magnesium salts and can damage equipment, while soft
water may be corrosive and therefore, it is important measuring and
knowing levels of hardness in your process water to maintain the
delicate balance between scaling and corrosivity.
• While some hardness may be acceptable in certain water quality
applications, others require zero hardness to prevent scaling and
damage to equipment. Therefore, water softening by either
precipitation or ion exchange is often necessary to remove hardness.
To optimize these processes, it is sometimes important to monitor
calcium and magnesium levels separately, along with total hardness.
5.
6. Determination of Hardness
Aim: Determine the total hardness of given water samples.
Requirements:
• Water sample
• Burette 25-30ml
• Glass funnel
• Pipette 1ml
• Flask
• Dropper
• Measuring cylinder
7. Reagents: EDTA, Eriochrome Black-T, NH2CL, Ammonia Buffer,
Magnesium Carbonate, 90% ethyl alcohol, Distilled water.
Reagent preparation:
• EDTA solution: 4gm EDTA and 0.1gm magnesium bicarbonate dissolve in 800 ml
distilled water.
• Eriochrome Black-T: 0.4gm Ericrome Black T, 4.5 gm hydroxylmine
hydrochloride add in 100ml 95% ethyl alcohol.
• Ammonia Buffer: Stock A: 16.9gm of NH4CL in 143ml of conc. NH4OH, Stock B:
1.25gm magnesium salt of EDTA dissolve in 50 ml distilled water. Mix both stock
solutions and dilute to 250ml with DDW. Dilute 10ml of the solution to 100ml
with DDW.
8. Procedure
1. The burette is filled with standardEDTA solution to the zero level.
2. Take 50ml sample water in flask. If sample having high Calcium content then take
smaller volume and dilute to 50ml.
3. Add 1ml Ammonia buffer.
4. Add 5 to 6 drop of Ericrome black – T indicator.The solution turns into wine red colour.
5. Note the initial reading.
6. Titrate the content against EDTA solution. At the end point colour changefrom wine
red to blue colour.
7. Note the final reading and record it. Repeat the process till we get concordantvalue.
8. Take 50ml sample in another flask and boiled it. (Add distilled water to get final
volume of water.)
9. Repeat step 3-7.
9. Observation
The colour of soluble distilled water and R.O water instantly changed
into blue while tap water and pond water turned wine red when
Erichrome black T was added and therefore after turned blue when
titrated against EDTA solution.
