My Chemistry Thread

[jgoudie]

You kind of answered your questions, you just need to think about what you just wrote. 

The loss of electrons happens in the reaction that occurs at the anode, thus the anode is surrounded by negative electrons, these electrons then leave and head towards the positive cathode where they are taken in.

The negative means a source of negative electrons, you can think off loss of electrons as "creation" of electrons if you want to, thus the anode has a negative charge.

Probably a stupid question, but why is the anode negatively charged, if that's where oxidisation (loss of electrons) is occurring?

[lzxnl]

Remember, this logic ONLY applies for a galvanic cell. For an electrolytic cell, the anode and cathode designations switch, but the half-cell polarities don't. Read my thread in the Chemistry Resources list in the VCE Chemistry forum.

[alchemy]

The negative means a source of negative electrons, you can think off loss of electrons as "creation" of electrons if you want to, thus the anode has a negative charge.

Oh right, that makes sense now that I think about it like that. I guess my mistake was thinking the electrode that accepted the electrons as being 'negatively charged' :/

[alchemy]

The density of liquid nitrogen is 0.807 g mL–1. If a person accidentally swallowed a 0.025 mL drop
of liquid nitrogen, what volume of nitrogen gas would be evolved in their body at 100.0 kPa and
37 °C?
A 0.018 mL
B 0.025 mL
C 19 mL
D 23 mL
E 37 mL

My answer is way off Actual answer is C.

[Yacoubb]

The density of liquid nitrogen is 0.807 g mL–1. If a person accidentally swallowed a 0.025 mL drop
of liquid nitrogen, what volume of nitrogen gas would be evolved in their body at 100.0 kPa and
37 °C?
A 0.018 mL
B 0.025 mL
C 19 mL
D 23 mL
E 37 mL

My answer is way off Actual answer is C.

Hey

Okay so:

1. Calculate mass of nitrogen gas:

Density = mass / volume
Thus, mass = 0.807 * 0.025 = 0.020175 g

2. Calculate number of moles

N = m / Mr = 0.020175 / 28 = 0.000720535 mol

3. Calculate volume of gas using pv = nRt

100 * v = 0.000720535 * 8.31 * 310
v = 0.01856L
v = 18.6 mL = 19mL, hence C

[alchemy]

Hey

Okay so:

1. Calculate mass of nitrogen gas:

Density = mass / volume
Thus, mass = 0.807 * 0.025 = 0.020175 g

2. Calculate number of moles

N = m / Mr = 0.020175 / 28 = 0.000720535 mol

3. Calculate volume of gas using pv = nRt

100 * v = 0.000720535 * 8.31 * 310
v = 0.01856L
v = 18.6 mL = 19mL, hence C

Thanks. I made a silly mistake again...lol.

[Yacoubb]

Thanks. I made a silly mistake again...lol.

It's all good

[alchemy]

I'm finding this question a bit hard to understand. If someone could just explain what the question is asking for, and perhaps reword it, I would be happy to attempt it myself.

Methanol, CH₃OH has a density of 0.787 g.cm^-3 at 25 degrees Celsius. A volumetric flask was found to be miscalibrated. The actual volume, when filled to the mark was 932.0 mL. If this flask is used to make a methanol solution of 0.800 molar, how much methanol (in ml) must be pipetted in, before it is diluted up to the mark?

[swagsxcboi]

I'm finding this question a bit hard to understand. If someone could just explain what the question is asking for, and perhaps reword it, I would be happy to attempt it myself.

Methanol, CH₃OH has a density of 0.787 g.cm^-3 at 25 degrees Celsius. A volumetric flask was found to be miscalibrated. The actual volume, when filled to the mark was 932.0 mL. If this flask is used to make a methanol solution of 0.800 molar, how much methanol (in ml) must be pipetted in, before it is diluted up to the mark?

okay so a density of 0.787 g.cm^3 means that for every cm^3, you have 0.787g of methanol.

Mr(CH3OH) = 32g/mol

so if we find out how many mols of methanol per cm^3 (aka mL, as 1cm^3 = 1mL),
n=m/Mr,   n= 0.024594 mols

since the actual volume of the volumetric flask is 932.0 mL, a quick C=n/V can give us how many mols of methanol we need to pipette.

n= C x V,  n = 0.8 x 0.932     n= 0.7456 mols of methanol required to make the flask have a 0.8M.

divide the amount of mols of methanol required by the amount of mols of methanol per mL.

0.7456/0.024594 = 30.3163 mL of methanol must be pipetted.

express to 3 sig figs, 30.3mL.

[alchemy]

Does Na⁺ have a greater atomic radius than F^-? If so, why? I got this question incorrect on a past chem test but wasn't sure why Na+ has a smaller atomic radius. Is it simply because it's a positive cation?

[hobbitle]

Well both ions have the same electron configuration, so their negative charge is the same, but Na has more protons than Fl .
The Na protons (because there are more of them) pull those electrons closer to the nucleus, reducing the atomic radius.

[alchemy]

Well both ions have the same electron configuration, so their negative charge is the same, but Na has more protons than Fl .
The Na protons (because there are more of them) pull those electrons closer to the nucleus, reducing the atomic radius.

But Na has an extra shell, therefore increasing it's radius, right? Idk...

[hobbitle]

But Na has an extra shell, therefore increasing it's radius, right? Idk...

The Na ION doesn't have the extra shell.
Only an Na neutral atom does.

[IndefatigableLover]

But Na has an extra shell, therefore increasing it's radius, right? Idk...

It won't have an extra shell  because it's an ion meaning that it'll have the same amount of shells as F^-
Edit: Beaten

[hobbitle]

As said in my first answer, both Na+ and Fl- have the same electron configuration ( that of Neon ).  Same number of electrons, same number of shells