Soccerboi's questions thread

[soccerboi]

What does inter particle bonding mean? Is it just the same as intermolecular forces of attraction? I'm a bit confused about inter particle, inter/intramolecular.

Also what on earth are ion dipole bonds?

[SenriAkane]

Interparticle bonding = bonds formed between molecules = intermolecular forces

ion-dipole is electrostatic attraction forces between an ion and a polar molecule

[soccerboi]

Thanks

Also, On the diagram of the electrophoresis gel shown below, draw a possible finished gel after the
amino acids have been separated, clearly labelling the locations of the glutamic acid and serine
amino acids.

Glutamic acid and serine are both heavier so why has it moved further than alanine?

[pi]

Are you looking at it the right way? It's hard to tell as the -ve and +ve signs aren't given

[vgardiy]

If this is from neap 2010, its because the pH is 6.0, meaning the Glutamic Acid and serine are both above their isoelectric points, so will be carrying a negative charge, moving them further towards the positive electrode, whereas alanine carries a neutral charge, so it moves through slower.

I think its a bit of a dodgy question overall, but I'm not sure about that.

[soccerboi]

sorry i forgot to say the left is negative and the right is positive

[soccerboi]

If this is from neap 2010, its because the pH is 6.0, meaning the Glutamic Acid and serine are both above their isoelectric points, so will be carrying a negative charge, moving them further towards the positive electrode, whereas alanine carries a neutral charge, so it moves through slower.

I think its a bit of a dodgy question overall, but I'm not sure about that.

Are isoelectric points even part of unit 3???

[vgardiy]

If this is from neap 2010, its because the pH is 6.0, meaning the Glutamic Acid and serine are both above their isoelectric points, so will be carrying a negative charge, moving them further towards the positive electrode, whereas alanine carries a neutral charge, so it moves through slower.

I think its a bit of a dodgy question overall, but I'm not sure about that.

Are isoelectric points even part of unit 3???

Thats why i thought it was dodgy. They dont even provide pKa's, so you cant actually infer anything about the isoelectric points.

[soccerboi]

A mass of 0.1373 g of freeze-dried sample of shellfish tissue is dissolved in 2.00 mL of nitric
acid, heated for 3 hours at 125°C and transferred to a 500.0 mL volumetric flask, where it is
made up to the mark with deionised water. A volume of 1.00 mL of this solution is then
further diluted to 250.0 mL in a second volumetric flask. AAS is used to measure the
absorbance of this solution, which is found to be 1.03.

a. What is the concentration, in μg L–1, of mercury in the 250.0 mL volumetric flask?
0.34 μg L–1 (from the graph)

b. Calculate the mass, in mg, of mercury in the shellfish sample.
NEED HELP HERE!
Answer is 0.021 mg

[Tonychet2]

A mass of 0.1373 g of freeze-dried sample of shellfish tissue is dissolved in 2.00 mL of nitric
acid, heated for 3 hours at 125°C and transferred to a 500.0 mL volumetric flask, where it is
made up to the mark with deionised water. <------- (ignore all this random information to throw u off because of no dilution factors)


A volume of 1.00 mL of this solution is then
further diluted to 250.0 mL in a second volumetric flask. AAS is used to measure the
absorbance of this solution, which is found to be 1.03.

a. What is the concentration, in μg L–1, of mercury in the 250.0 mL volumetric flask?
0.34 μg L–1 (from the graph)

0.34 ug = 0.34x10^-6g per liter...

you have 250ml so you divide 0.34 x 10^-6 by 4 to get 8.5 x 10^-8g

the dilution factor was 250 because of 1ml to 250ml so multiply  8.5 x 10^-8g by 250 to give you the answer ... 2.1 x 10^-5g (0.021 mg )

[soccerboi]

A mass of 0.1373 g of freeze-dried sample of shellfish tissue is dissolved in 2.00 mL of nitric
acid, heated for 3 hours at 125°C and transferred to a 500.0 mL volumetric flask, where it is
made up to the mark with deionised water. <------- (ignore all this random information to throw u off because of no dilution factors)


A volume of 1.00 mL of this solution is then
further diluted to 250.0 mL in a second volumetric flask. AAS is used to measure the
absorbance of this solution, which is found to be 1.03.

a. What is the concentration, in μg L–1, of mercury in the 250.0 mL volumetric flask?
0.34 μg L–1 (from the graph)

0.34 ug = 0.34x10^-6g per liter...

you have 250ml so you divide 0.34 x 10^-6 by 4 to get 8.5 x 10^-8g

the dilution factor was 250 because of 1ml to 250ml so multiply  8.5 x 10^-8g by 250 to give you the answer ... 2.1 x 10^-5g (0.021 mg )

How come we don't multiply by (500.0/1.00) to get the mass in 500ml? isn't this the volume for the sample, not 1ml?

[soccerboi]

In mass spec equations, how do we know where to put the charge? Is it just where fragment comes off, or always at the end of the formula?
Like the one below, if the CH3O comes off, how do u write the fragment that will show the peak on the spectrum? CH3COOCO⁺?

Also how do u write the semistructural formula for it? CHCOOCOOCH3 or CHOOCCOOCH3?

[charmanderp]

I think you can put square brackets around the entire molecule and then have a + on the outside. Or alternatively, put it where to free radical came off.

[soccerboi]

oh thanks, and about writing the semi structural formula, does it matter if its -COOCOO- or OOCCOO- in the above compound?

[charmanderp]

Personally I think having two Cs (or Hs or Os or whatever) next to each other not only looks silly but it can be awfully confusing, so avoid it wherever possible.