quick Gen chem multiple choice

[kov82]

---

Members don't see this ad.

which has the lowest melting point?
a) pure water
b) 1 M NaCl
c) 1 M sucrose
d) 1 M MgCl2
e) 1 M HCl

my logic was that water had the least solutes dissolved in it so it had the weakest forces within so it would melt the easiest (assuming these are all dissolved in water which would be why they stated "pure water") so my answer was "a" but the said the answer is "d" the explanation given is that a solution with the lowest melting point will have the greatest # of particles dissolved in it, does that make sense? am I incorrectly applying boiling point rules to melting point? is it a book error?


this one is easy but I got it backwards:

A student heated a 120 g sample of a hydrated salt when it was heated to the point when the H2O was removed the remaining powder weighed 30g, what is the ratio of the mass of salt to the mass of H2O in the hydrate?
a) 2:1
b)3:1
c)4:1
d)1:3
e)1:4

I said choice d but the book says choice b its 30/90 = 3/9 = 1/3 so why b?

 

[pbure9]

which has the lowest melting point?
a) pure water
b) 1 M NaCl
c) 1 M sucrose
d) 1 M MgCl2
e) 1 M HCl

my logic was that water had the least solutes dissolved in it so it had the weakest forces within so it would melt the easiest (assuming these are all dissolved in water which would be why they stated "pure water") so my answer was "a" but the said the answer is "d" the explanation given is that a solution with the lowest melting point will have the greatest # of particles dissolved in it, does that make sense? am I incorrectly applying boiling point rules to melting point? is it a book error?


this one is easy but I got it backwards:

A student heated a 120 g sample of a hydrated salt when it was heated to the point when the H2O was removed the remaining powder weighed 30g, what is the ratio of the mass of salt to the mass of H2O in the hydrate?
a) 2:1
b)3:1
c)4:1
d)1:3
e)1:4

I said choice d but the book says choice b its 30/90 = 3/9 = 1/3 so why b?

for the first one, D is correct. Water actually has the highest melting point amongst those choices. When you add electrolytes to water, they decrease the point and increase the boiling point. MgCl2 will give you 3 ions in solution, so it will decrease MP the most.

deltaT = m x kb x i

where m is molality and i is number of dissolved particles (ex. glucose will only give you an i=1).

and the second one is odd. I'd say d too. Is this barrons lol?

 

[doc toothache]

which has the lowest melting point?
a) pure water
b) 1 M NaCl
c) 1 M sucrose
d) 1 M MgCl2
e) 1 M HCl

A student heated a 120 g sample of a hydrated salt when it was heated to the point when the H2O was removed the remaining powder weighed 30g, what is the ratio of the mass of salt to the mass of H2O in the hydrate?

Are you sure you paraphrased the questions properly?

 

[kov82]

nope its some "clep" book with practice problems, and yes I did phrase it correctly, thanks for the reply guys, the second one must be a mistake in the book.

 

[ktpinnock]

this one is easy but I got it backwards:

A student heated a 120 g sample of a hydrated salt when it was heated to the point when the H2O was removed the remaining powder weighed 30g, what is the ratio of the mass of salt to the mass of H2O in the hydrate?
a) 2:1
b)3:1
c)4:1
d)1:3
e)1:4

I said choice d but the book says choice b its 30/90 = 3/9 = 1/3 so why b?[/QUOTE]

Because it asked for the mass of the H20 in the hydrate not the salt and the hydrate together. so mass of the hydrated salt - the mass of salt = the mass of the H20.
Which is 90. so 30/90

 

[doc toothache]

which has the lowest melting point?
a) pure water
b) 1 M NaCl
c) 1 M sucrose
d) 1 M MgCl2
e) 1 M HCl

nope its some "clep" book with practice problems, and yes I did phrase it correctly, thanks for the reply guys, the second one must be a mistake in the book.

As phrased, the question is asking the lowest melting points of pure substances rather than solutions.

 

[pbure9]

which has the lowest melting point?
a) pure water
b) 1 M NaCl
c) 1 M sucrose
d) 1 M MgCl2
e) 1 M HCl




As phrased, the question is asking the lowest melting points of pure substances rather than solutions.

but they give you molarities of each, meaning they are in solution, no?
If anyone has the new destroyer, this problem is similar to number 34 in the Chem.

 

[kov82]

ktpinnock you actually quoted my calculation, so I know how to calculate it, but my answer was 1:3 the books answer was 3:1 its asking for the ratio of the mass of salt to the mass of H2O in the hydrate, the mass of the salt was 30, the mass of H2O is 90, so the ratio is 1:3, the book says the answer is 3:1, I'm thinking its a book error

doc toothache, like I said in my first post, I suppose since they stated "pure water" you can assume that its 1M NaCl (in water) for choice "b" etc..

 

[doc toothache]

ktpinnock you actually quoted my calculation, so I know how to calculate it, but my answer was 1:3 the books answer was 3:1 its asking for the ratio of the mass of salt to the mass of H2O in the hydrate, the mass of the salt was 30, the mass of H2O is 90, so the ratio is 1:3, the book says the answer is 3:1, I'm thinking its a book error

doc toothache, like I said in my first post, I suppose since they stated "pure water" you can assume that its 1M NaCl (in water) for choice "b" etc..

Eyes engaged, brain disengaged.