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A couple of question...


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#1 floss

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Posted 05 May 2007 - 04:09 PM

Just a couple of questions that I'm not sure about, proabably really easy ones but anyway...

Uranium ore is converted into uranium (IV) fluoride, UF4, to produce fuel for nuclear power stations. In a second process, the uranium (IV)fluoride is converted into UF6 as shown.
UF4 (s) + F2 (g) ------> UF6 (g)
Name the type of bonding in UF6 (g)


^^I'm not sure how you would know this.

EDIT: Is it to do with NOF and hydrogen bonding?

In an experiment to find the enthlpy of solution of potassium hydroxide, KOH, a student added 3.6 g of the solid to the water in the polystyrene cup and measured the temperature rise. From this it was calculated that the heat energy produced in the reaction was 3.5kJ.
Use this information to calulate the enthalpy of solution of potassium hydroxide.


^^I have absolutely no idea where to start this...unsure.gif

Thanks! biggrin.gif

Edited by F.J, 05 May 2007 - 04:10 PM.

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#2 will_789

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Posted 05 May 2007 - 04:31 PM

QUOTE(F.J @ May 5 2007, 05:09 PM) View Post
In an experiment to find the enthlpy of solution of potassium hydroxide, KOH, a student added 3.6 g of the solid to the water in the polystyrene cup and measured the temperature rise. From this it was calculated that the heat energy produced in the reaction was 3.5kJ.
Use this information to calulate the enthalpy of solution of potassium hydroxide.


^^I have absolutely no idea where to start this...unsure.gif

Thanks! biggrin.gif


You do know what to do here...

3.6g of KOH gave out 3.5KJ of energy

Find the gfm of KOH

Then

(gfm of KOH) gave out xKJ of energy

Then use cross multiplication...
If you want further explanation leme know smile.gif


#3 floss

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Posted 05 May 2007 - 04:42 PM

Thank you so much! unsure.gif I feel so stupid now, but at least I got the right answer!
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#4 will_789

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Posted 05 May 2007 - 04:43 PM

QUOTE(F.J @ May 5 2007, 05:42 PM) View Post
Thank you so much! unsure.gif I feel so stupid now, but at least I got the right answer!

Woop!
Those type of questions are usually (delta)H=cm(delta)T. but in this case they save you all the hassel!

#5 ad absurdum

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Posted 05 May 2007 - 05:57 PM

QUOTE(F.J @ May 5 2007, 05:09 PM) View Post
Just a couple of questions that I'm not sure about, proabably really easy ones but anyway...

Uranium ore is converted into uranium (IV) fluoride, UF4, to produce fuel for nuclear power stations. In a second process, the uranium (IV)fluoride is converted into UF6 as shown.
UF4 (s) + F2 (g) ------> UF6 (g)
Name the type of bonding in UF6 (g)


^^I'm not sure how you would know this.
The key is in the (g), which tells you that the compound is in the gaseous state. Is this likely to be ionic or covalent?

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#6 floss

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Posted 05 May 2007 - 07:27 PM

Covalent? unsure.gif
If I've got that wrong I'm going to kick myself. Hard.
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#7 ginneswatson

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Posted 05 May 2007 - 08:15 PM

Chemistry is full of 'rules' that can be broken and 'white lies' that have to be told until you're old enough to be told the 'truth' (or at least the next 'white lie').

Standard grade lets you think metal to non-metal = ionic and non-metals only = covalent. Black and white.

Higher starts to plant the idea that there are shades of grey. Properties change gradually as you move across a row in the Periodic Table. Metals towards the middle of the Periodic Table often form compounds that are less than 100 % ionic. Electronegativity values help. A big difference (e.g. Cs & F) almost certainly leads to electron transfer and ionic properties. Little difference (e.g. C and H) leads to more or less equal sharing. Somewhere in between (e.g H & F) leads to unequal sharing, polar covalent bonding.

The 'surprise' is that some compounds containing metals (e.g. Al & Cl) have differences in electronegativity that point to polar covalent rather than ionic. Sure enough, AlCl3 exists as molecules and has much lower melting & boiling points than expected. Covalent Bonding with polar-polar attractions between molecules. However, when electrolysed, the AlCl3 molecules break apart to form Al3+ ions and Cl ions and conducts. Ionic Bonding.

The bottom line is forget 'rules' and, to a certain extent 'expect the unexpected'.

Properties are the best guide to the bonding structure. Be on your toes.





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