What is the mole fraction of chloride ions..?

[Smooth Operater]

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What is the mole fraction of chloride ions in a 1 m
solution of NaCl? (Atomic weights: Na = 23, Cl = 35)

A. 1/3
B. 1/2
C. 35/38
D. 1
E. None of the above

the correct answer E. But I am not sure how to arrive to the answer. Thanks!

 

[dudewhensmydat]

Ah; I just can't figure it out. I was trying to use the density & MM of water to get something going, but couldn't do it. Was there any other info stated?

 

[Manyak222]

its 35/58

58 being the total of both in 1 mole.
Hey quick question. when are you taking your DAT?

What is the mole fraction of chloride ions in a 1 m
solution of NaCl? (Atomic weights: Na = 23, Cl = 35)

A. 1/3
B. 1/2
C. 35/38
D. 1
E. None of the above

the correct answer E. But I am not sure how to arrive to the answer. Thanks!

 

[dat_student]

What is the mole fraction of chloride ions in a 1 m
solution of NaCl? (Atomic weights: Na = 23, Cl = 35)

A. 1/3
B. 1/2
C. 35/38
D. 1
E. None of the above

the correct answer E. But I am not sure how to arrive to the answer. Thanks!

m = molality = moles of solute / kg of solvent

1 m = 1 mole of NaCl / 1 kg of H2O

1 kg of H2O = 1000 g H2O (i.e. 1000 g / 18g/mole = ~55.5 moles)

1 mole of NaCl = 1 mole of Na+ plus 1 mole of Cl-

mole fraction of Cl ions = 1 mole / (1 mole + 1 mole + 55.5 moles) (i.e. 1 / 57.5)

 

[Smooth Operater]

Manyak222, I got the same answer as you did at first try, but actually we are wrong. We need to include the mole of water 😛 tricky I am taking the Canadian DAT on Nov. Why ask?

 

[dudewhensmydat]

Manyak222, I got the same answer as you did at first try, but actually we are wrong. We need to include the mole of water 😛 tricky I am taking the Canadian DAT on Nov. Why ask?

Wait, so what exactly is the answer?

 

[aranjuez]

Can we be clear in the future as to whether the problem involves "M" or "m." It makes a big difference. I know it sounds mean, and I realize it's unintentional sometimes, but I'm sure there are very competent people on the forums that would love to help but don't know whether you're asking about M or m.

Sorry if I sound rude. Just an observation.

 

[Smooth Operater]

the question give in term of "m" 😛 That's why we gonna include the mole of water.

 

[Smooth Operater]

Wait, so what exactly is the answer?

Datstudent is right. see above post