When alum is added to the waste water containing calcium ions which compound is formed as a precipitate?
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Answer:
Surface waters must be treated to remove turbidity, color and bacteria. The object of coagulation (and subsequently flocculation) is to turn the small particles of color, turbidity and bacteria into larger flocs, either as precipitates or suspended particles. These flocs are then conditioned so that they will be readily removed in subsequent processes. Technically, coagulation applies to the removal of colloidal particles. We define coagulation as a method to alter the colloids so that they will be able to approach and adhere to each other to form larger floc particles.
Colloid Stability...
Before discussing colloid removal, we should understand why the colloids are suspended in solution and cannot be removed by sedimentation or filtration. Very simply, the particles in the colloid range are too small to settle in a reasonable time period and too small to be trapped in the pores of a filter. For colloids to remain stable they must remain small. Most colloids are stable because they possess a negative charge that repels other colloids particles before they collide with one another.
Colloid Destabilization...
Since colloids are stable because of their surface charge, in order to destabilize the particles, we must neutralize this charge. Such neutralization can take place by addition of an ion of opposite charge to the colloid. Since most colloids found in water are negatively charged, the addition of sodium ions (Na+) should reduce the charge. As we would have predicted, then higher the concentration of sodium we add, the lower the charge, and therefore the lower the repelling forces around the colloid. If, instead of adding a monovalent ion such as sodium, we add a divalent or trivalent ion, the charge is reduced even faster. In fact, it was found by schulze and Hardy that one mole of a trivalent ion can reduce the charge as much as 30 to 50 moles of a divalent ion and as much as 1,500 to 2,500 moles of a monovalent ion.
When alum is added to the waste water containing calcium ions which compound is formed as a precipitate? Explanation: When alum is added to a waste water containing calcium salts Al (OH)3 is precipitated