Alkalinity of a water sample indicates its concentration of which species?

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Multiple Choice

Alkalinity of a water sample indicates its concentration of which species?

Alkalinity reflects the water’s buffering capacity to neutralize acids, and in most natural and treated waters that buffering comes mainly from bicarbonate ions (HCO3−). When acid is added, bicarbonate reacts to form carbonic acid, which then releasing CO2, helping keep the pH from dropping quickly. Because bicarbonate is typically the dominant buffering species in common drinking water, alkalinity effectively indicates its concentration. The other ions listed don’t provide buffering to the same extent: chloride and nitrate are largely non-buffering, and sulfate contributes far less to alkalinity in usual waters. At higher pH, carbonate and hydroxide can contribute more, but for ordinary potable water, bicarbonate is the primary contributor.

Alkalinity reflects the water’s buffering capacity to neutralize acids, and in most natural and treated waters that buffering comes mainly from bicarbonate ions (HCO3−). When acid is added, bicarbonate reacts to form carbonic acid, which then releasing CO2, helping keep the pH from dropping quickly. Because bicarbonate is typically the dominant buffering species in common drinking water, alkalinity effectively indicates its concentration. The other ions listed don’t provide buffering to the same extent: chloride and nitrate are largely non-buffering, and sulfate contributes far less to alkalinity in usual waters. At higher pH, carbonate and hydroxide can contribute more, but for ordinary potable water, bicarbonate is the primary contributor.

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