CSE 2009 Chem Questions

[kyzoo]

1. For one of the multiple choice questions, it asks which of the following energy production method is the most sustainable

A. Hydroelectric Power
B. Coal (something like this)
C. Hydrogen
D. Nuclear Fission

So my question is...how is hydroelectric power more sustainable than hydrogen...isn't there like, more hydrogen in the universe than water 0.o?

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2. I'm really confused about what cryolite does. Does it lower the melting temperature of alumina? Or does it act as a solvent for alumina?

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3. How does chlorine being more electronegative than iodine mean that HOCl has a higher Ka value than HOI. I couldn't understand the solutions, and I can't visualize how being more attractive to electrons means greater extent of ionization.

[happyhappyland]

hydrogen needs to be produced from somewhere and that process requires energy more than hydroelectric power. In hydroelectric power essentially "nature" due to water's kenetic energy from a higher point falling to a lower point produces energy.

Crylolite lowers the melting temp of alumina allowing the process to run at lower temps and thus saving energy.

[Xavier1234]

1. For one of the multiple choice questions, it asks which of the following energy production method is the most sustainable

A. Hydroelectric Power
B. Coal (something like this)
C. Hydrogen
D. Nuclear Fission

So my question is...how is hydroelectric power more sustainable than hydrogen...isn't there like, more hydrogen in the universe than water 0.o?

--------------------

2. I'm really confused about what cryolite does. Does it lower the melting temperature of alumina? Or does it act as a solvent for alumina?

---------------------

3. How does chlorine being more electronegative than iodine mean that HOCl has a higher Ka value than HOI. I couldn't understand the solutions, and I can't visualize how being more attractive to electrons means greater extent of ionization.

adding into what happyhappyland said, H gas is also extremely flammable. not very viable in this day and age.

[vexx]

3. How does chlorine being more electronegative than iodine mean that HOCl has a higher Ka value than HOI. I couldn't understand the solutions, and I can't visualize how being more attractive to electrons means greater extent of ionization.

Well the more electronegative it is, the more the conjugate base is stabilised, so it makes it a stronger acid... and the stronger an acid is, the higher the Ka value as it proceeds further to the right..
you really don't need to know more detail.

[Greggler]

For the HOCl one just look at the databook/electro negative series.

A question i have about this exam, is i think that  last question, where you were expected to pull a half equatoin out of your ass... something involving a carbonate ion and hydrogen i think. i had no idea, how did everyone else find it?

[kyzoo]

3. How does chlorine being more electronegative than iodine mean that HOCl has a higher Ka value than HOI. I couldn't understand the solutions, and I can't visualize how being more attractive to electrons means greater extent of ionization.

Well the more electronegative it is, the more the conjugate base is stabilised, so it makes it a stronger acid... and the stronger an acid is, the higher the Ka value as it proceeds further to the right..
you really don't need to know more detail.

...I want to know in detail =X It's hard to remember random facts that don't even make sense

Greggler: Yea I was stumped that too 0.o They don't even have a H+ or OH- ion in that half equation.

[Greggler]

yeah, doubt it would be something to stress over.

[vexx]

3. How does chlorine being more electronegative than iodine mean that HOCl has a higher Ka value than HOI. I couldn't understand the solutions, and I can't visualize how being more attractive to electrons means greater extent of ionization.

Well the more electronegative it is, the more the conjugate base is stabilised, so it makes it a stronger acid... and the stronger an acid is, the higher the Ka value as it proceeds further to the right..
you really don't need to know more detail.

...I want to know in detail =X It's hard to remember random facts that don't even make sense

Greggler: Yea I was stumped that too 0.o They don't even have a H+ or OH- ion in that half equation.

errr well.
the more stable the conjugate base is, the more the electrons can move around. and so the negative charge are able to be spread out on the electronegative atoms... which means the stronger the electronegivity, the more they will be able to accept the partial negative charge.. which lead to a stable conjugate base.. therefore enabling it to be a stronger acid, hence improving its ability to have a greater K value (stronger acid=stronger K which you should already know)
hope that makes sense LOL.

[kyzoo]

wait wait...wat does negative charges have to do with acids and bases =X

[vexx]

Sorry didn't see this one either, chem forum didn't show any new posts o-O?

Ahh well, sorry to confuse you, i think its why its best to just know
higher electroneg=higher acid strength=higher Ka

but basically using this as example "HOCl has a higher Ka value than HOI"
- acid ionisation, causes a negative ion to be produced, it is negative as it has an extra electron (Cl- or I-), the electronegativity of the ion, means that the more electronegative, the more the negative charge (electron) will be attracted to the ion. so the conjugate base OCl- can more readily accept the negative charge, making it more stable.
And, the more electronegative it is, the more easily it can cut the O-H bond, making it more easily ionised, and hence increasing its ability to attract that negative ion when the conjugate base is formed.
so = stronger acid.
:p