Question

Two friends Heena and Shikha were discussing which term is better for expressing the concentration of a solution Molality or Molarity ? Shikha told Heena that Molality is considered better for expressing the concentration as compared to Molarity and also gave justification to her answer: (i) What would be the explanation of Shikha? (ii) What is the difference between molality & molarity? (iii) Mention the values shown by Shikha.

Answer 1

(i) Molarity is termed as the amount of moles of a compound dissolved in an amount of solvent. Molality is termed as the number of moles of solute divided by the number of kilograms of solvent.

(ii) Molarity is affected by changes in temperature but molality is not affected by the changes in temperature.

(iii) Molarity affected by changes in pressure but molality is not affected by changes in pressure.

(iv) Molarity may be imprecise but molality is very accurate.

(v)                     $Molarity\quad (M)\quad =\quad \frac { Moles\quad of\quad solute }{ Solution\quad in\quad litres } \\ Molality\quad (m)\quad =\quad \frac { Moles\quad of\quad solute }{ Kg\quad of\quad solvent }$

Answer 2

MOLARITY= MOLES OF SOLUTE/SOLUTION IN LITER


MOLALITY= MOLES OF SOLUTE/MASS OF SOLVENT IN kg