Question

Which of the following solutions would have the highest vapor pressure.

A)	0.2 M MgCl2

B)	0.2 M NaCl

C)

0.1 M KCl

D)	0.2 M Na2CO3

E)	0.1 M MgCl2

Answer 1

relative lowering of vapour pressure is directly proportional to vant hoff factor .

so at first we can see that all are ionic compound and they are 100% dissociatable in aqueous solution.

A . MgCl2 = 3 particles, 1 Mg and 2 Cl

B. NaCl = 2 particles , 1 Na and 1 Cl

C. KCl = 2 particles , 1 K and 1 Cl

D .Na2CO3 = 3 particles , 2 Na and 1 CO3

E . MgCl2 = 3 particles , 1 Mg and 2Cl

now we see that their concentration is also different so 0.2 is 2 times 0.1 so we multiply each 0.2 M by 2 because they have 2 times no of particle in 0.1 comparison .

A . MgCl2 = 3*2 = 6 times particles

B. NaCl = 2*2 = 4 times particles

C = KCl = 2 * 1 = 2 times particles (because it has 0.1 molarity concentration)

D.Na2CO3 = 2 * 3 = 6 times particles

E . MgCl2 = 3 times partices

for high vapour pressure we should have less no of particles and we can see 0.1 M KCl have less no. of particles so we have higher vapour pressure

please note here I convert all the dissociating particle according to 0.1 mole .

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