question_answer 44)

Calculate the depression in the freezing point of water when 10 g of CH3CH2CHClCOOH is a dried to 250 g of water, Ka = 1.4 x 10–3, Kf  = 1.86 K kg mol–1

Answer:

Step I. To find degree of dissociation of acid Molar mass of CH3CH2CHClCOOH i.e., C4H7ClO2 = 12 x 4 + 7 x 1 + 35.5 + 32 = 122.5 g mol?1 Moles in 10 g of CH3CH2CHClCOOH mole Mass of solvent = 250 g = 0.25 kg Molality of the solution (m) If  is the degree of dissociation of CH3CH2CHCICOOH, then CH3CH2­CHClCOOH  CH3CH2CHClCOO+H+  Initial conc.         C mol L?1                              ?             ? At equilibrium   C(1 ? ) mol L?1                       C        C  very small and 1 ?   1) or Step II. To Calculate van't Hoff factor Initial moles             1             ?        ?   of moles After dissociation   1 ?            Total no. of moles after dissociation= 1 +           Step- III. To find depression in freezing point