Sub-topic 1
2013 · National Semifinal
Free
Cations responsible for permanent water hardness
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Sub-topic 2
2013 · National Semifinal
Premium
Why temporary water hardness is so named (removable by boiling)
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Sub-topic 3
2017 · National Semifinal
Premium
Mass of slaked lime needed to soften water containing a given mass of calcium hydrogencarbonate
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