TrueTears question thread

[TrueTears]

thank you ed_saifa

[chem-nerd]

the line between the O and the Na is a negative charge rather than a bond

so it would be -COO^-Na⁺

[TrueTears]

Thanks chem-nerd

Another one:

A standard 0.103 M sodium carbonate was prepared in a volumetric flask. 25.00mL aliquots were measured into a conical flask and titrated against a dilute solution of approximately 0.2M hydrochloric acid. Which of the following indicators is most suitable for use in this titration?
A. Methyl red
B. Phenol red
C. Phenolphthalein
D. Bromothymol blue

[chem-nerd]

check this post for the electronic version of this lisachem exam (it has the answers at the end)
http://vcenotes.com/forum/index.php/topic,13001.msg152181.html#msg152181

[TrueTears]

Yeah, I have the answers, but I don't understand them lol.

[lacoste]

A standard 0.103 M sodium carbonate was prepared in a volumetric flask. 25.00mL aliquots were measured into a conical flask and titrated against a dilute solution of approximately 0.2M hydrochloric acid. Which of the following indicators is most suitable for use in this titration?
A. Methyl red
B. Phenol red
C. Phenolphthalein
D. Bromothymol blue

I don't fully get the solutions either. This is how I would solve it:

-sodium carbonate is a weak base
-dilute HCl is a medium (usually strong) acid

(If) dilute HCl is strong acid then you can ONLY use methyl red.
because:
*phenolphthalein is for strong base/weak acid
*bromothymol blue is for strong base/strong acid
*phenol red is med strong base/ weak acid

use elimination method. even if it gets to two ans.

that is how i would do it!

[TrueTears]

^^ Thanks

A triglyceride with a molar mass of 884 is formed by reacting glycerol with an excess of linoleic acid (contains 2 double bonds). 1.00g of the triglyceride is reacted with excess (addition reaction). Calculate the mass of needed for this reaction.

[ed_saifa]

What's the answer?

[TrueTears]

1.08 g.

I've tried doing it, but my working doesn't let me to 1.08g lol

[ed_saifa]

For one mol of the triglyceride, you will need 6 mols of Br2. This is because there are 6 double bonds in the triglyceride.

[dekoyl]

I did because 2 on each fatty acid and three fatty acids on triglyceride so 3x2=6.

[TrueTears]

Oh shi* lol I just did 2 double bonds sigh...

Thanks everyone!!!

[TrueTears]

I know this question was just asked by NE2000 but is a double bond (alkene) considered as a functional group?

[/0]

yep, it was on one of the vcaa exams

[TrueTears]

thanks for that /0

just another question

Say you got an amide group -CONH-, but when you put that through a IR spectrometer would there be a peak between 1670 - 1750 which is the C=O peak?

The sample exam for VCAA 2008 says no, which is the answer I got after a process of elimination, since all the other answers were wrong, but I just want to make sure where exactly does the C=O on the data sheet 1670 - 1750 corresponds to? Is it only for carboxy or what?

Thanks