Analysis of hard water Introduction

Analysis of hard water
Introduction

Hard water is water that has high mineral content (in contrast with soft
water). Hard water has high concentrations of calcium, magnesium and iron
ions.
These ions are called hardening ion.

In low concentrations, these ions are not considered harmful for domestic
use, but when present in higher concentrations these ions interfere with
the cleansing action of soaps and accelerate the corrosion of steel pipes,
especially those carrying hot water

Soaps are sodium or potassium salts of higher fatty acids such as stearic
acid, C17H35COOH . Soaps such as C17H35COONa+ are very effective
cleansing agents so long as they remain soluble in water. They react with
Ca2+ and Na2+ ions present in hard water and form an insoluble sticky
precipitate of calcium and magnesium salts of fatty acids known as scum and
thus interfere in the cleansing action of soap.

C17H35COONa+ (aq) + Ca2+ (aq) C17H35COOCa2+ +2Na+

Hardness of water can be defined as the soap – consuming capacity of water,
or the capacity of precipitation of soap as a characteristic property of
water that prevents the lathering of soap. It is responsible for the
formation of boiler scales on tea kettles and vessels used for heating
water. The boiler scale reduces the efficiency of transfer of heat because
it is a bad conductor of heat. Formation of boiler scale in the pipes
carrying hot water reduces the rate of flow of water in them. On extreme
cases due to overheating the boiler or the pipes may break due to
overheating. The boiler scale consists of primarily of the carbonates of
hardening ions.

Ca2+ (aq) + 2HCO3-(aq)
CaCO3(s)+CO2(g)+H2O(l)

The hardening ions enter into water as a result of reaction between
slightly acidic rain water and mineral deposits. Ground water becomes hard
as it flows through underground lime – stone deposits. The water from the
deep wells has higher degree of hardness as compared with water from
shallow wells because of greater interaction with the lime – stone
deposits.CO2 dissolved in water, makes it slightly acidic and helps in
dissolved lime-stone deposits.

CO2 (aq) + CaCO3(s) + H2O(l) Ca2+
(aq) + 2HCO3-(aq)

Types of hard water

Hard water can be classified into two:-

Temporary Hard water
Permanent Hard water

Temporary hardness

Temporary hardness is caused by a combination of calcium ions and
bicarbonate ions in the water. it can be removed by boiling the water or by
the addition of lime (calcium hydroxide). Boiling promotes the formation of
carbonate from bicarbonate and precipitates calcium carbonate out of the
solution, leaving water that is softer upon cooling.

The following is the equilibrium reaction when calcium carbonate (CaCO3) is
dissolved in water.

CaCO3(s) + CO2(g) +H2O(l) Ca2+
(aq) + 2HCO3-(aq)

Upon heating, less CO2 is able to dissolve into the water. Since there is
not enough CO2 around, the reaction cannot proceed from left to
right, and therefore the CaCO3 will not dissolve rapidly. Instead, the
reaction is forced to the left to re-establish equilibrium, and solid CaCO3
is formed.

Boiling the water will remove hardness as long as the solid CaCO3 that
participates out is removed. After cooling, if enough time passes, the
water will pick up CO2 from the air and the reaction will again proceed
from left to right ,allowing the CaCO3 re-dissolve into the water.

Permanent hardness

Permanent hardness is hardness that cannot be removed by boiling. It is
usually caused by the presence of calcium and magnesium sulphates and or
chlorides which become more soluble as the temperature rises. Despite the
name, permanent hardness can be removed using a water softener or ion
exchange column, where the calcium and magnesium ions are exchanged with
the sodium ions in the column.

Hard water causes scaling, which is the left – over mineral deposits that
are formed after the hard water had evaporated .this is also known as lime
scale the scale can clog pipes , ruin water heaters , coat the inside of
tea and coffee pots and decrease the life of toilet flushing units.

Hardening must be constantly monitored to avoid costly breakdowns in
contact with water. Hardness is controlled by the addition of chemicals and
by large-scale softening with zeolites (Na2Al2SiO8.xH2O) and ion exchange
resins.

Effects of hard water

These are advantages and disadvantages for people who live in hard water
areas.

Disadvantages of hard water
It is difficult to form lather with soap.
Scum may form in a reaction with soap thus wasting soap.
Lime scale (a hard crust) forms inside kettles. This wastes energy
whenever you boil a kettle.
Hot water pipes fur up. Lime scale starts to coat the inside of the
pipes which can eventually can get blocked up.

Advantages of hard water
Some people prefer the taste.
Calcium ions in the water are good for children's teeth and bones.
It helps to reduce heart disease.
A coating of lime scale onside copper pipes or especially old lead
pipes sops poisonous salts dissolving into water

Effects on skin

Some confusion may arise after a first experience with soft water. Hard
water does lather well with soap and leaves a "clean feeling". Soft water
lathers better than hard water but leaves a "slippery feeling" on the skin
after use with soap. Some providers of water softening equipment claim
that the "slippery feeling" after showering in soft water is due to "clean
skin" and absence of friction causing soap scum.

However, the chemical explanation is that softened water, because of its
sodium content, has a much reduced ability to combine with the soap film on
the body; therefore, the soap is much more difficult to rinse off.
Solution are to use less soap or a synthetic liquid body wash.

SOFTENING

It is often considered desirable to soften hard water. This is because the
calcium and Magnesium ions block the oil emulsifying action of soap due to
the formation of insoluble scum. Large amount of soap have to be used to
counteract this. Most modern soaps and detergents contain ingredients that
at least partly prevent this effect and detergents are available that are
chemically completely unaffected by the hardness. This makes hardness
removal/softening an optional rather than a necessary water treatment
except possibly in the case of extremely hard water. Where softening is
practiced it is often recommended to soften only the water sent to domestic
hot water systems so as to prevent damage due to scale formation in water
heaters. Another reason for this is to avoid adding sodium or potassium
from the softener to cold water taken for human consumption while still
providing softening for hot water used in washing and bathing.

PROCESS

A water softener works on the principle of cation or ion exchange in which
hardening ions are exchanged for Sodium or Potassium ions, effectively
reducing the concentration of hardness to tolerable levels and thus making
the water softer and giving it a smoother feeling.

The most economical way to soften household water is with an ion exchange
water Softener. This unit uses Sodium Chloride (NaCl) to recharge beads
made of the ion exchange resins that exchange hardness mineral ions for
sodium ions. Artificial or natural zeolites can also be used.

As the hard water passes through the beads, the hardness mineral ions are
preferentially absorbed, displacing the sodium ions. This process is
called ion exchange. When bead or sodium zeolite has a low concentration
of sodium ions left, it is exhausted, and can no longer soften water. The
resin is recharged by flushing with salt water. The high excess
concentration of sodium ions alter the equilibrium between the ions in
solution and the ions held on the surface of the resin, resulting in
replacement of the hardness mineral ions on the resin or zeolite with
sodium ions. The resulting saltwater and mineral ion solution is then
rinsed away, and the resin is ready to start the process all over again.
This cycle can be repeated many times. Potassium chloride may also be used
to regenerate the resin beads. It exchanges the hardness ions for
potassium. It also will exchange naturally occurring sodium for potassium
resulting in sodium-free soft water.

Some softening processes in industry use the same method, but on a much
larger scale. These methods create as enormous amount of salty water that
is costly to treat and dispose of.

MEASUREMENT

The simple way to determine the hardness of water is the lather/froth test:

When agitated, lathers easily in soft water but not in hard water. More
exact measurements of hardness can be obtained through a wet titration.
Although water hardness usually measures only the total concentrations of
Calcium and Magnesium (the two most prevalent, divalent metal ions), iron,
Aluminium, and Manganese may also be present at elevated levels in some
geographical locations.

The degree of hardness in water depends on the extent of hardening ions
present in water. The concentration of hardening ions is a water sample is
generally expressed as though the hardness is due exclusively to CaCO3.
The units or hardness is mg CaCO3/litre which is same as parts per million
(ppm) CaCO3.

A General Classification Of Hard Water is given below:

" " "
"Hardness (ppm CaCO3) "Classification "
"<15ppm "Very soft water "
"15ppm-50ppm "Soft water "
"50ppm-100ppm "Medium hard water "
"100ppm-200ppm "Hard water "
">200ppm "Very hard water "

Experiment

Aim
To determine the hardness of a water sample

Requirements
250ml conical flask , funnel , beaker , burette , pipette.
Standard EDTA(Na2H2Y)solution ,buffer solution(pH=10),Erichrome Black
T(EBT) indicator

Theory
The concentration of hardening ions in water can be determined by a
titration technique, the titrant is the disodium salt of ethylene-
diaminetetraaceticacid

In aqueous solution Na2H2Y dissociates into Na+ and H2Y2- ions.Ca2+ and
Mg2+ react with H2Y2- to form stable complexes in a solution having pH of
about 10.a buffer solution containing ammonia and ammonium ions is used to
maintain the pH of the solution around 10.
For the detection of the end point Erichrome Black T (EBT) is used as
indicator EBT forms complex ions with Ca2+ and Mg2+, but binds more
strongly to Mg2+ ions. Since only a small amount of EBT is added, only a
small amount of Mg2+ ions is used in the formation of complex and no Ca2+
ions are used.

EBT indicator is sky-blue in solution but its complex with Mg2+ ions, [Mg-
EBT]2+, is wine red

Mg2+(aq) + EBT(aq) [Mg-EBT]2+ (aq)
Sky-blue
wine red

Thus, during titration when indicator is added to hard water ,the initial
colour is wine red.

When the titrant is added, H2Y2- complexes with free Ca2+ and Mg2+ present
in water and finally removes Mg2+ ions from the [Mg-EBT]2+ complex ions.
As a result the colour of the solution from wine red to sky blue.

[Mg-EBT]2+ (aq) + H2Y2-(aq)
MgY2- + 2H+(aq) + EBT(aq)
Wine red
sky blue

It may be mentioned here that for the end point to appear, Mg2+ ions must
be present in the solution. Therefore, a small amount of Mg2+ (as same
salt) is added to the buffer solution and an equivalent amount of Na2H2Y
is also added so that the added Mg2+ ions do not affect the amount of H2Y2-
used during titration.

Indicator

Erichrome Black T(EBT)

End point

Wine red to sky blue colour.

Wine red to sky blue

Procedure

Take about 100ml of the water sample to be analyzed. If the water
sample contains suspended impurities, it should be subjected to
simple filtration. If the water sample is acidic to litmus, add 1M
NH3 drop wise until it becomes basic to litmus.
Rinse the burette with Na2H2Y solution and then fill it with the
solution. Record the initial reading.
Pipette out 25.0ml of the given sample of water in the conical
flask. Add 1ml of the buffer (pH=10) solution and 2 drops EBT
indicator. The colour of the solution becomes wine red at this stage.
Titrate the above solution with standard Na2H2Y solution. At the
end point the wine red colour disappears and the solution becomes
blue(or purple) in colour. Note the final reading of the burette.
Repeat the titration 3 to 4 times to get a concordant reading.

Observations

Morality of the standard Na2H2Y solution =0.01M.
Volume of water taken for each titration = 20.0ml.

Burette readings
tap water

"S no. "Initial reading "Final reading "Volume of Na2H2Y used "
"1 "0.0 "4.4 "4.4ml "
"2 "4.4 "8.9ml "4.5ml "
"3 "8.9 "13.4ml "4.5ml "

Concordant readings – 4.5ml

pool water

"S no "Initial reading "Final reading "Volume of Na2H2Y used "
"1 "0.0 "6.3 "6.3ml "
"2 "6.3 "12.7 "6.4ml "
"3 "12.7 "19.1 "6.4ml "


sea water

"S no "Initial reading "Final reading "Volume of Na2H2Y used "
"1 "0.0 "79.9 "79.9ml "
"2 "0.0 "80.0ml "80.0ml "
"3 "0.0 "80.0ml "80.0ml "


Calculations

tap water

Let the volume of titrant used be = 4.5 ml
Morality of titrant solution = 0.01M

Moles of titrant used = M x
V

1000

=0.01 x 4.5

1000

= 45 x 10-6

Mass of Na2H2Y = Moles of Ca2+ = 0.01 x 4.5
= 45 x 10-6

1000

Mass of equivalent CaCO3 = 0 .01 x
4.5 x100g = 45x10-6x102

1000

=45x10-4 mg

Mass of CaCO3 per litre

= 45 x 10-4 x 1000

20

=50 x 45 x10-4

=225 x 10-3mg/l

Hardness =
= 225 x 10 -3 x 106

= 225 x 10 -3 x 106

103

= 225 ppm
Calculations

Pool water

Let the volume of titrant used be = 6.4 ml

V

1000

=0.01 x 6.4

1000

= 64x 10-6

Mass of Na2H2Y = Moles of Ca2+ = 0.01 x 6.4=
45 x 10-6

1000

6.4x100g = 64x10-6x102

1000

=64x10-4 mg


= 64 x 10-4 x 1000

20

=50 x 64 x10-4

=320 x 10-3mg/l

Hardness =
= 320 x 10 -3 x 106

= 320x 10 -3 x 106

103

= 320 ppm
Calculations

Sea water

Let the volume of titrant used be = 80 ml

V

1000

=0.01 x 80

1000

= 80 x 10-5

Mass of Na2H2Y = Moles of Ca2+ = 0.01 x 80 =
80 x 10-5

1000

80 x100g = 80x10-5x102

1000

=80x10-3 mg


= 80 x 10-3 x 1000

20

=50 x 80 x10-3

=4000 x 10-3mg/l

Hardness =
= 4000 x 10 -3 x 106

= 4000 x 10 -3 x 106

103

= 4000 ppm

Result

The degree of hardness of the following water samples are:-

Tap water - 225ml
Pool water - 320ml
Sea water - 4000ppm

Index

Certificate
Acknowledgements
Introduction
Aim, theory and procedure
Observations and calculations
Result

Certificate

This is to certify that Eben Mathew of class XII has completed the
investigatory project as per the requirement of CBSE practical work during
the year 2010-2011

…………………….. ………………………..
Signature of teacher
Signature of examiner

Acknowledgements

I would like to express my gratitude to my teacher Mrs. Rajasree karnavar
for providing us with an opportunity to perform this experiment.

I would like to express my appreciation to Mrs. Mary Thomas our lab
assistant for her guiding support throughout the experiment.

Lastly a sincere thanks to my partners Rahul Mahajan and Nabeel for the
great deal of effort put into this experiment.

Chemistry Project
Analysis of hard water

BY:
Eben Mathew

Class: XII-K

Analysis of hard water Introduction

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