A water with pH 7.4 has the following analysis. Please determine the exact total

Question

A water with pH 7.4 has the following analysis. Please determine the exact total hardness and alkalinity in units of mg/L as CaCO3.

Na+ -- 10.25 <-- concentration in mg/L

K+ -- 1.15 <-- concentration in mg/L

NH3+ -- 1.39 <-- concentration in mg/L

Ca2+ -- 278.0 <-- concentration in mg/L

Mg2+ -- 134.80 <-- concentration in mg/L

NO3- -- 0.85 <-- concentration in mg/L

Cl- -- 6.34 <-- concentration in mg/L

SO42- -- 30.16 <-- concentration in mg/L

HCO3- -- 248.00 <-- concentration in mg/L

Explanation / Answer

1 / Calculations for total hardness-

hardness causing impurities --------------------------------- equivalents of CaCO3--------------------------------------------------------

Ca 2+ --------------------------------------------------------------- ( 278 x 100/40 ) = 695 mg / L ----------------------------------------Mg 2+ ---------------------------------------------------------------( 134.8 x 100 /24 ) = 561.66 mg / L -----------------------------------

HCO3 - -----------------------------------------------------------[248 x 100 / ( 61 x2 )]= 203.28 mg / L ------------------------------------

Therefore total hardness = ( 695.00 + 561.66 + 203.28 ) = 1459.94 mg / L of CaCO3

2 / Calculations for alkalinity -

Salts----------------------------------------------------------- alkalinity in terms of CaCO3 (mg / L )-------------------------------------------Na + -----------------------------------------------------------[ 10.25 x 100 / ( 23 x 2 ) ] = 22.28 ----------------------------------------------

K + ------------------------------------------------------------[ 1.15 x 100 / ( 39 x 2 ) ] = 1.47 ----------------------------------------------

NH3 + -------------------------------------------------------- [ 1.39 x 100 / ( 18 x2 ) ] = 3,86 ----------------------------------------------

Ca 2+ (ie calcium alkalinity ) ------------------------ [ 278.0 x 100 /40 ] = 695.00 -------------------------------------------

Mg 2+ ( Magnesium alkalinity ) ---------------------[ 134.80 x 100 /24 ] = 561.67------------------------------------------

NO3 - ignored -----------------------------------------------------------------------------------------------------------------------------------------------

SO4 2- ignored --------------------------------------------------------------------------------------------------------------------------------------------

Cl- -----------------------------------------------------------------[ 6.34 x 100 / 35.45 x 2 ] = 9.20 ----------------------------------------------

HCO3 - --------------------------------------------------------- [ 248.00 x 100 / 61 x2 ] = 203.28 -----------------------------------------

Therefore , total alkalinity = 1496.76 mg / L as Ca CO3

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