Pre-exam questions

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Wow, I have a lot of them, thanks if you can please help with them...

1.
I
II
III
IV

The substance(s) that contain(s) molecules that are attracted to molecules of the same substance by hydrogen bonds is (are)
A. I.                        B. I and IV.                        C. I, II and IV.                        D IV.

(I picked B because Hydrogen bonds are formed between Hydrogen and F, O, N, but it isn't right :/)

2.
Which one of the following statements is correct?
A. Oil and water mix to form a colourless solution.
B. ALL ionic compounds dissolve readily in water.
C. Ethanol () and water mix to form a solution.
D. ALL polar molecular substances dissolve readily in water.

(D and E seem pretty good at the moment, not quite sure which one)

3.
Which of the following molecules would be expected to be the most soluble in water?
A.                         B.
C.                      D.

(C and D are both polar, and although O has higher electronegativity, it has the H attached to it, which sort of counteracts that... does it?)

4.
An oxide of formula was extracted from a sample of beach sand. If the oxide contains 40% by mass oxygen, the molar mass of X would be
A.                         B.                         C.                         D.

 ()

5.
Which of Sodium Chloride and Lithium Chloride would have the higher melting temperature? Why?

That's all... for now! 

[mark_alec]

1. D is correct. Hydrogen bonds will only form if the hydrogen is attached to oxygen, nitrogen or fluorine.

2. Any statement that generalises a property (e.g. all/none these) is very unlikely to be correct, since there are almost always exceptions to the rule. One that should immediately spring out as being correct is C, since alcoholic beverages contain ethanol dissolved in water.

3. C and D are both polar, but ethanol forms hydrogen bonds with water, so it will be the most soluble.

4. D If 40% of the substance is oxygen by weight, then


5. Not sure, the answer is NaCl, as for why, better let coblin explain.

[/0]

Thanks, I just have a few concerns

In question 1, couldn't hydrogen bonding occur as in the attached diagram?

For question 4, is capital M the molecular mass or the mass? It seems like it is being used as the mass... I'm still a bit confused about that

[jeremykleeman]

I am pretty sure that your example will not work, as the hydrogens bonded to the carbon aren't going to be "slightly positive" (as required for hydrogen bonding) given the small difference in electro negativity between carbon and hydrogen.

[mark_alec]

Thanks, I just have a few concerns

In question 1, couldn't hydrogen bonding occur as in the attached diagram?

For question 4, is capital M the molecular mass or the mass? It seems like it is being used as the mass... I'm still a bit confused about that

Should be the molar mass of O2 divided by the molar mass of XO2.

[cootcoot]

with question 4, XO2

i thought that it would be O : 40/16                  X  : 60/48
                                        = 2.5                       =1.25   

                                          2.5/1.25                  1.25/1.25
                                         =2                           =1


theerfore RMM is 48?...?