Question
Which aqueous solution has higher concentration-1 molar or 1 molal solution of the same solute? Give reason.
Case I:
When density of solvent is 1g/ mL: In aqueous solution, density of water is normally taken as 1. This means that 1m solution has 1 mole of the solute dissolved in 1000g or 1000mL of the solvent. At the same time 1M solution contains 1 mole of the solute in 1000mL solution, which is the volume of both the solute and solvent present in the solution. This clearly shows that the solvent present in 1M solution is less as compared to 1m solution. Therefore, 1M solution is more concentrated than 1m solution.
Case II:
When density of the solvent is less than 1g/ mL: This means that the volume of solvent (mass/ density) will be more as compared to its mass. Thus, 1M solution will be less concentrated than 1m solution.
Case III:
When density of the solvent is more than 1g/ mL: This means that the volume of solvent will be less than its mass. Under these circumstances, 1M solution will be more concentrated than 1m solution.
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| Time/sec | Total pressure/atm |
| 0 | 0.30 |
| 300 | 0.50 |