Alkalinity in Water

Alkalinity in LIMS• W_W_CO3_SM2320B_A as CO3 (v * n * 50000 ) / s ) * 0.6• W_W_ALKALINITY_HCO3_SM_A Alkalinity as HCO3 ( v * n * 61000 ) / s• W_W_HCO3_SM2320B_A Bicarbonate as HCO3 ( v * n * 61000 ) / s• W_W_ALKALINITY_SM_A Alkalinity as mg CaCO3 (v * n * 50000 ) / s• W_W_HCO3_AS_CO3_SM2320B_A Bicarbonate as CO3 (v * n * 30000 ) / s• W_W_HYDROXIDE_SM2320B_A Hydroxide as OH (v * n * 17000 ) / s

SM

There are three sources of alkalinity in water samples

Hydroxide Alkalinity OHˉCarbonate Alkalinity CO32-

Bicarbonate Alkalinity HCO3ˉ

Total Alkalinity is the sum of all

Equations

H+ + OH- H2O (neutral)

H+ + CO32- HCO3

- HCO3

- + H+ H2CO3

(slightly basic) (acidic)

HCO3- + H+ H2CO3

(acidic)

Equations

OH- + H+ H2O (neutral – EP1)

CO32- + H+ HCO3

- (slightly basic – EP1)

HCO3- + H+ H2CO3 (acidic – EP2)

HCO3- + H+ H2CO3 (acidic – EP2)

Equations

OH- is a strong base.

HCO3- is a weak acid

If I have more OH- than HCO3-, it completely neutralizes it and I

just have OH-If I have more HCO3

- than OH-, then it partially neutralizes it and I detect only HCO3

-

Method

+

100 mL

Check pH

Start Titration with 0.1 N HCl to pH 8.3Record V1 of HCl

Continue Titration with 0.1 N HCl to pH 4.5Record V2 of HCl

Cases

• Sample Volume • First Volume of HCl from sample pH to pH 8.3• Total Volume of HCl from sample pH to pH 4.5….??!!!

The possibilities for V1(PP) and TV(TT)VV11 = 0 = 0TV = 0 TV = 0

VV11 < ½ < ½ TVTVVV11 = ½ TV= ½ TVVV11 > ½ TV > ½ TV

VV11 = = TVTV

Only If sample pH is less than 4.5

By Means that no acid consumption from pH 8.3 to pH 4.5

Calculations

• OH- Alkalinity Is expressed as OH- or as CaCO3

• CO32-Alkalinity Is expressed as CO3

- or as CaCO3

• HCO3- Alkalinity Is expressed as HCO3

- or as CaCO3

• Total Alkalinity Is expressed as CaCO3

So if you want to report the total alkalinity, you have to express all

types (if present) as CaCO3

Example of all possibilities for V1 and TV

P = 0 P < ½ T P = ½ T P > ½ T P = T

Hydroxide Alkalinity 0 0 0 2P – T T

Carbonate Alkalinity 0 2P 2P 2 (T-P) 0

Bicarbonate Alkalinity T T – 2P 0 0 0

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CalculationsP = 0 0

P < ½ T 0

P = ½ T Hydroxide Alkalinity as OH- 0

P > ½ T N*((2*P)-T)*17000/A

P = T N*T*17000/A

P = 0 0

P < ½ T N*(2*P)*60000/A

P = ½ T Carbonate Alkalinity as CO3 N*(2*P)*60000/A

P > ½ T N*2*(T-P)*60000/AP = T 0

P = 0 N*T*61000/A

P < ½ T N*(T-(2*P))*61000/AP = ½ T Bicarbonate Alkalinity as HCO3 0

P > ½ T 0

P = T 0

Total Alkalinity as CaCO3 (X_1* 50/17)+(X_2*50/60)+(X_3*50/61

P = 0 P < ½ T P = ½ T P > ½ T P = T

A Sample Volume 100 100 100 100 100B Normality of HCl 0.1 0.1 0.1 0.1 0.1C Sample pH 8.6 8.6 8.6 8.6 8.6P Volume of HCl to pH 8.3 0 1 2 3 4T Volume of HCl to pH 4.5 4 4 4 4 4

Hydroxide Alkalinity X1 0 0 0 100 200

Carbonate Alkalinity X2 0 100 200 100 0Bicarbonate Alkalinity X3 200 100 0 0 0Total Alkalinity 200 200 200 200 200

Total Alkalinity =Total Alkalinity = N T 50000 / V

as

Ca

CO

3

X1 + X2 + X3

P = 0 P < ½ T P = ½ T P > ½ T P = T

A Sample Volume 100 100 100 100 100B Normality of HCl 0.1 0.1 0.1 0.1 0.1C Sample pH 8.6 8.6 8.6 8.6 8.6P Volume of HCl to pH 8.3 0 1 2 3 4V2 Volume of HCl from pH 8.3 to 4.5 4 4 4 4 4T Total Volume of HCl to pH 4.5 4 5 6 7 8

Hydroxide Alkalinity X1 0 0 0 -50 400Carbonate Alkalinity X2 0 100 200 400 0Bicarbonate Alkalinity X3 200 150 0 0 0Total Alkalinity 200 250 200 350 400

Total Alkalinity =Total Alkalinity =

X1 + X2 + X3

N T 50000 / V

as

Ca

CO

3

Case Study

CO32-HCO3

-

Case Study

CO32-HCO3

-

H+

Case Study

CO32-HCO3

- H+

Case Study

CO32-HCO3

- H+

H+

Case Study

CO32-HCO3

-H+ H+

Case Study

CO32-HCO3

-H+ H+

H+

Case Study

CO32-HCO3

-H+ H+ H+

Case Study

CO32-HCO3

-H+ H+ H+

Total H+ = 3

Two of them for CO32-

One of them for HCO32-

Case Study

H2CO3-

Total H+ = 3

Two of them for CO32-

One of them for HCO32-

H2CO3-

Case Study

CO32-HCO3

- 2 Mole3 Mole

Case Study

CO32-HCO3

- 4 Equivalent3 Equivalent

X EquivalentH+

Case Study

CO32-HCO3

-

X Equivalent H+

4 Equivalent 3 Equivalent

Case Study

CO32-HCO3

-

Equivalent = N VEquivalent = N V

Equivalent = N VH+

Case Study

CO32-HCO3

-

X Equivalent H+ 2 Equivalent

HCO3-

3 Equivalent

2 Equivalent

P = 2

Case Study

HCO3-

5 Equivalent H+

HCO3-

3 Equivalent

2 Equivalent

5 Equivalent

V2 = 5

Case Study

HCO3-

7 Equivalent H+

CO3-

2 Equivalent

2 Equivalent

3 Equivalent

T = 7

Case Study

HCO3-

7 mLH+

CO3-

2 mL

2 mL

3 mL

Calculate Carbonate Alkalinity

Calculate Bicarbonate Alkalinity

Calculate Total Alkalinity

P = 2 mL

T = 7 or 5 mL

Case Study

Calculate Carbonate Alkalinity

Calculate Bicarbonate Alkalinity

Calculate Total Alkalinity

P = 2 mL

T = 7 or 5 mL

P = 0

Carbonate Alkalinity as CO3

0

P < ½ T N*(2*P)*60000/A

P = ½ T N*(2*P)*60000/A

P > ½ T N*2*(T-P)*60000/A

P = T 0

N*(2*P)*60000/A

0.1*(2*2)*60000/100 = 240 as CO3

0.1*(2*2)*50000/100 = 200 as CaCO3

P = 2 mL

P = 2 mL

Case Study

Calculate Carbonate Alkalinity

Calculate Bicarbonate Alkalinity

Calculate Total Alkalinity

P = 2 mL

T = 7 or 5 mL

N*(T-(2*P))*61000/A

0.1*(7-(2*2))*61000/A = 183 as HCO3

0.1*(7-(2*2))*50000/A = 150 as CaCO3

P = 0

Bicarbonate Alkalinity as HCO3

N*T*61000/AP < ½ T N*(T-(2*P))*61000/A

P = ½ T 0P > ½ T 0

P = T 0

T = 7 mL

T = 5 mL0.1*(5-(2*2))*50000/A = 50 as CaCO3

0.1*(5-(2*2))*61000/A = 61 as HCO3 T = 5 mL

T = 7 mL

ComparisonP < ½ T

A Sample Volume 100B Normality of HCl 0.1C Sample pH 8.6P Volume of HCl to pH 8.3 2T Volume of HCl to pH 4.5 7.0X1 Hydroxide Alkalinity as OH- 0X2 Carbonate Alkalinity as CO3 240X3 Bicarbonate Alkalinity as HCO3 183X4 Total Alkalinity as CaCO3 350

P < ½ T

A Sample Volume 100B Normality of HCl 0.1C Sample pH 8.6P Volume of HCl to pH 8.3 2T Volume of HCl to pH 4.5 5.0X1 Hydroxide Alkalinity as OH- 0X2 Carbonate Alkalinity as CO3 240X3 Bicarbonate Alkalinity as HCO3 61X4 Total Alkalinity as CaCO3 250

Calculations

P = 0 P < ½ T P = ½ T P > ½ T P = T

A Sample Volume 100 100 100 100 100B Normality of HCl 0.1 0.1 0.1 0.1 0.1C Sample pH 8.6 8.6 8.6 8.6 8.6P Volume of HCl to pH 8.3 0.0 1 2 3 4.0T Volume of HCl to pH 4.5 4.0 4.0 4.0 4.0 4.0X1 Hydroxide Alkalinity as OH- 0 0 0 34 68X2 Carbonate Alkalinity as CO3 0 120 240 120 0X3 Bicarbonate Alkalinity as HCO3 244 122 0 0 0X4 Total Alkalinity as CaCO3 200 200 200 200 200

Three sources of alkalinity depends on sample pH No Treatments, dilution or preservation Titrate to pH 8.3 then record the HCl volume Complete titration to pH 4.5 Record the Total volume of HCl For Total Alkalinity use TV in the calculation formula For other types of alkalinity, refer to the table .. it depends on first volume

of HCl to reach pH 8.3 and the rest of total volume.. Express Total Alkalinity as CaCO3