annahinh's (modified) Chemistry Question

[physics]

0.148g of a metal carbonate exactly reacts with 20ml of 0.1M HCl. The formula of the metal carbonate is most likely to be
A. Li2CO3   B. Na2CO3   C.MgCO3   D. Sr CO3

i got A the ans is D
i did
n=0.02 *0.1 =0.002mol
M =m/n and that gives me 74 and ....now i have lost myself

SHortened this question below to important bits
There are 2 samples of CaCO3 both weighing 2g. Sample 1 has large pieces of CaCO3 and sample 2 has smaller pieces.
100ml of 0.5M HCl is added to sample 1 and at 18C
equation : CaCO3 + 2HCl--> CaCl2 + H20 +CO2

First question asks for the amount in excess of Hcl which is 0.47684L (used pV=nRT)
then calculate the total change in mass recorded by the balance when all the calcium carbonate has been used up?


my 1000 posts :3  :smitten:

[kyzoo]

Not neccesarily. The retention time of a substance does not depend on its molar mass, but rather its tendency to adsorb onto the stationary phase and desorb into the mobile phase. You can have two substances with the same molecular formula (and hence molar mass) but with different retention times due to differing structures.

[naved_s9994]

Not neccesarily. The retention time of a substance does not depend on its molar mass, but rather its tendency to adsorb onto the stationary phase and desorb into the mobile phase. You can have two substances with the same molecular formula (and hence molar mass) but with different retention times due to differing structures.

That is absolutely correct.

[stonecold]

Not neccesarily. The retention time of a substance does not depend on its molar mass, but rather its tendency to adsorb onto the stationary phase and desorb into the mobile phase. You can have two substances with the same molecular formula (and hence molar mass) but with different retention times due to differing structures.

That is absolutely correct.

+1

kyzoo is on the money.

just to add, for example, a polar molecule will have a high affinity to a mobile phase such as water(which is also polar).  but if the mobile phase is a non polar solution, then it will be less likely to desorb than if it were a non polar molecule...

[fady_22]

However for some groups of hydrocarbons, the strength of adsorption onto the stationary phase increases (especially in gas chromatography) with molar mass, and so the retention time increases. This is only because they have similar structure.

I think.

[naved_s9994]

However for some groups of hydrocarbons, the strength of adsorption onto the stationary phase increases (especially in gas chromatography) with molar mass, and so the retention time increases. This is only because they have similar structure.

I think.

True...
The analyte does take a certain amount of time to equilibrate between the stationary and mobile phase. If the speed of the mobile phase is high, and the analyte has a strong atraction for the stationary phase, then the analyte in the mobile phase will move ahead of the analyte in the stationary phase.

I believe its lipids ?

_____________________________________________________________________________________________

But I believe this now over and above the VCE Chemistry Study Design Requirements...

[qshyrn]

However for some groups of hydrocarbons, the strength of adsorption onto the stationary phase increases (especially in gas chromatography) with molar mass, and so the retention time increases. This is only because they have similar structure.

I think.

But I believe this conversation, is now over

wtf

[physics]

THANKS FOR THE HELP!

+ the retention time is just the time that the machine runs for rihgt? thanks

[kyzoo]

Nop, it's the time it takes for a substance from the sample mixture to travel from the starting end of the chromatography column, to the point where it is picked up by the detector.

[physics]

Nop, it's the time it takes for a substance from the sample mixture to travel from the starting end of the chromatography column, to the point where it is picked up by the detector.

thank you :]

[physics]

HELP ME PLEASE


1000 post