You have 5 liters of water with a concentration of 15 mg/L of Calcium dissolved in it. You leave the water in the sun and 2.5 liters of water evaporate. What is the concentration now?

Question

BlackTom AI · Accepted Answer

The scenario presents 5 liters of water with a calcium concentration of 15 mg/L, and 2.5 liters of water evaporate, leaving 2.5 L behind. To find the new concentration, begin by computing the total amount of calcium initially present: 5 L × 15 mg/L = 75 mg of calcium. Evaporation reduces the volume but does not remove calcium, so the total calcium mass remains 75 mg in the remaining 2.5 L of water. Now calculate the new concentration: 75 mg / 2.5 L = 30 mg/L.
Option 1: 3 mg/L — this would require a tenfold decrease from the original concentration, which would imply loss of calcium or a much larger increase in volume; since mass is conserved and volume decreased, this is incorrect.
Option 2: 1875 mg/L — this would require the same 75 mg to be confined to a tiny volume of 0.04 L (75 mg / 0.04 L ≈ 1875 mg/L); the actual remaining volume is 2.5 L, so this is not feasible here and incorrect.
Option 3: 12.5 mg/L — this would result from 75 mg spread over 6 L (75 mg / 6 L = 12.5 mg/L); our final volume is 2.5 L, not 6 L, so this option is incorrect.
Option 4: 30 mg/L — this aligns with the conservation of mass (75 mg) divided by the new volume (2.5 L), producing 30 mg/L; this is the correct outcome given the scenario.

You have 5 liters of water with a concentration of 15 mg/L of Calcium dissolved in it. You leave the water in the sun and 2.5 liters of water evaporate. What is the concentration now?单项选择题

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