Textbook Answer wrong or..?

[barydos]

I thought the correct choice would be D, but the answers says it's B.
Isn't density = mass/volume though?

[pi]

I think the density of gases changes with temperature, hence density can't be calculated with certainty.

However my answer is based on distant memories, hope a real chemist gets to your q too haha

[Stick]

I think the density of gases changes with temperature, hence density can't be calculated with certainty.

However my answer is based on distant memories, hope a real chemist gets to your q too haha

I was thinking the same thing, but I think that would also render II incorrect as well since that could change. The only piece of information which can be determined consistently in that information is mol. Generally answers are made more clear than this so don't stress, but it's good to know nonetheless.

[curry_bro]

Answer is B because... what pi said hahaha
no joke hes right. i conformed with a brilliant Pharmacy student (chem god) from monash.
dont worry. this guy got a 50 in chem, so u can have faith that the answer is B.

[Stick]

Can someone then explain how II is also correct then? :S

[MonsieurHulot]

Can someone then explain how II is also correct then? :S

Well w/v=(unsurprisingly) weight/volume
We are given both weight and volume, hence it can be calculated.
Density cannot be calculated with any certainty without assuming a temperature, ie. SLC, as the equation for density of gases is= MP/RT. As a temperature is required, and none is given, it cannot be calculated.
w/v% can be calculated, as there is no temperature value needed.

Spoiler

I think.

[Stick]

Ah, now I see. Thanks.

[barydos]

I was thinking the same as stick, wouldn't variance in temperature affect the volume, and ultimately the %w/v??!

[teletubbies_95]

So, Density = m/V

Volume varies with temperature. Generally, as T increases, V increases due to increased collisions with the walls of the container. So as T increases, D decreases. In this question , there has been no indication of the temperature , so we cannot accurately measure the density .

Question looks easy , but tricky ! Good luck

[barydos]

Alright thanks everyone

[FlorianK]

But isn't the definition of density mass per Volume. We are given the mass and we are given the Volume so why shouldn't we in the same way as II be able to calculate the density.

[Stick]

Yeah I'm still a bit confused over it all. I think this was just a bad question.

[MonsieurHulot]

But isn't the definition of density mass per Volume. We are given the mass and we are given the Volume so why shouldn't we in the same way as II be able to calculate the density.

Because, according to Wikipedia, the equation for the density of a gas is not simply m/v, it's MP/RT.

[Stick]

Lol Wikipedia Well I guess you learn something new every day! Although, I don't ever recall learning this in Unit 2 AOS2 Chemistry. :S

[FlorianK]

Because, according to Wikipedia, the equation for the density of a gas is not simply m/v, it's MP/RT.

Well stupid copying without thinking yourself from Wikipedia made you loose, meaning I won.
I will now prove to you that p(density)=m/V=MP/RT
normal stoichiometry formula is m=n*M
density formula is p=MP/RT
ideal gas equation is P=nRT/V

Sub in ideal gas equation into density formula and you get
p=MnRT/(RTV)=Mn/V=m/V

I like winning