civilsid
Civil/Environmental
- Feb 6, 2007
- 21
Civil P.E. study question I ran into but would like someone experienced to translate this into English. It is somewhat confusing to me:
If 0.1 mol/L of sodium is sufficient to destabilize a colloid, then which of the following doses will be equally effective?
1.00× 10 ?4 mol/L of alum
1.43× 10 ?4 mol/L of alum
1.00× 10 ?3 mol/L of ferric chloride
1.43× 10 ?3 mol/L of ferric chloride
Solution:
The Shultz-Hardy rule states that the destabilization of a colloid by an indifferent electrolyte is brought about by ions of opposite charge to that of the colloid, and that coagulation effectiveness increases with charge. Thus, monovalent, divalent, and trivalent species should be effective approximately in the ratio of 1 : 100 : 1000. In most practical systems, the Shultz-Hardy rule is "violated" because the electrolytes are not different. Inorganic compounds added to water react with solution electrolytes and form complexes and precipitates. Hence the coagulation power for monovalent, divalent, and trivalent species is taken as 1:60:700.
The conventional choices for appropriate coagulants with appropriate characteristics are alum (Al2SO4·14H2O), ferric chloride (FeCl3), or ferric sulfate (Fe(SO4)3·H2O).
Alum and ferric chloride are trivalent coagulants, therefore the dose corresponding to 0.1 mol/L sodium is
concentration of alum / concentration of sodium = 1/700
concentration of alum = concentration of sodium / 700
= (0.1 mol/L)/ 700
= .000143 mol / L of alum
The answer is B.
If 0.1 mol/L of sodium is sufficient to destabilize a colloid, then which of the following doses will be equally effective?
1.00× 10 ?4 mol/L of alum
1.43× 10 ?4 mol/L of alum
1.00× 10 ?3 mol/L of ferric chloride
1.43× 10 ?3 mol/L of ferric chloride
Solution:
The Shultz-Hardy rule states that the destabilization of a colloid by an indifferent electrolyte is brought about by ions of opposite charge to that of the colloid, and that coagulation effectiveness increases with charge. Thus, monovalent, divalent, and trivalent species should be effective approximately in the ratio of 1 : 100 : 1000. In most practical systems, the Shultz-Hardy rule is "violated" because the electrolytes are not different. Inorganic compounds added to water react with solution electrolytes and form complexes and precipitates. Hence the coagulation power for monovalent, divalent, and trivalent species is taken as 1:60:700.
The conventional choices for appropriate coagulants with appropriate characteristics are alum (Al2SO4·14H2O), ferric chloride (FeCl3), or ferric sulfate (Fe(SO4)3·H2O).
Alum and ferric chloride are trivalent coagulants, therefore the dose corresponding to 0.1 mol/L sodium is
concentration of alum / concentration of sodium = 1/700
concentration of alum = concentration of sodium / 700
= (0.1 mol/L)/ 700
= .000143 mol / L of alum
The answer is B.
