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How was it?


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#221 Tiger

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Posted 31 May 2005 - 05:51 PM

QUOTE(tupacshakur @ May 31 2005, 06:24 PM)
QUOTE(sai @ May 31 2005, 05:23 PM)
the other product was glycerol i think

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yep

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biggrin.gif

#222 YIC

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Posted 31 May 2005 - 05:51 PM

QUOTE(Tiger @ May 31 2005, 06:50 PM)
QUOTE(tupacshakur @ May 31 2005, 06:23 PM)
QUOTE(Soph.E. @ May 31 2005, 05:22 PM)
- I said both hydrogen and carbon dioxide would be left at the end because:

metal + acid                = salt + hydrogen gas
metal carbonate + acid = salt + water + carbon dioxide gas

and there was a metal and a metal carbonate reacting with the acid. (Think I'm remembering this right!) Standard grade stuff though really isn't it... always catches you out  huh.gif

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yaas i wrote that aswell

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me to biggrin.gif

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I never put that but hopefully I will get half a mark for saying hydrogen only....just kidding tongue.gif

#223 Pooch

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Posted 31 May 2005 - 05:51 PM

There was one about some trout farming type chap adding limestone to his loch to increase the pH, it went from four to six. Then it asked you something about the conc. of H+ ions. It was increasing or decreasing by a factor of either two or one hundred, can anyone remember their answer?

#224 tupacshakur

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Posted 31 May 2005 - 05:53 PM

QUOTE(Pooch @ May 31 2005, 05:51 PM)
There was one about some trout farming type chap adding limestone to his loch to increase the pH, it went from four to six. Then it asked you something about the conc. of H+ ions. It was increasing or decreasing by a factor of either two or one hundred, can anyone remember their answer?

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decreased by factor of 100
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#225 YIC

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Posted 31 May 2005 - 05:53 PM

I think I said decreasing by factor of 100

#226 sai

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Posted 31 May 2005 - 05:54 PM

thats rite becos it came up in a past paper thats wot it was

#227 tupacshakur

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Posted 31 May 2005 - 05:55 PM

is writing starch showed colour change ok to write instead of writing it was the end point of rection?
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#228 bred

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Posted 31 May 2005 - 05:55 PM

QUOTE(ally @ May 31 2005, 06:46 PM)
Disillation is boiling and condensing water. When you boil it you break intermolecular bonds, you break the bonds between the water molecules, not the actual covelant bonds between the atoms. Then when you condense it you reform the bonds between the water molecules.

So  it would be C, Van der Waals bonds are broken then remade.

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Ah, ok, thanks. I'll not let it bug me!
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#229 gary

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Posted 31 May 2005 - 05:55 PM

QUOTE(ally @ May 31 2005, 05:50 PM)
QUOTE(gary @ May 31 2005, 06:46 PM)
Said it showed the end point of the reaction.

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Well done!

That was the 30,000th post on HSN. tongue.gif biggrin.gif

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Cool

#230 e-unit

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Posted 31 May 2005 - 05:55 PM

QUOTE(Soph.E. @ May 31 2005, 06:22 PM)
- I said both hydrogen and carbon dioxide would be left at the end because:

metal + acid                = salt + hydrogen gas
metal carbonate + acid = salt + water + carbon dioxide gas

and there was a metal and a metal carbonate reacting with the acid. (Think I'm remembering this right!) Standard grade stuff though really isn't it... always catches you out  huh.gif

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But copper doesnt react with acids so it was only co2

#231 bred

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Posted 31 May 2005 - 05:56 PM

Coolio. Man, the 20,000th post was only around the time of the English exam, maybe a little before, wasn't it? ohmy.gif
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#232 gary

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Posted 31 May 2005 - 05:56 PM

QUOTE(YIC @ May 31 2005, 05:53 PM)
I think I said decreasing by factor of 100

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Yeah that is right that question is in many past papers.

#233 Tiger

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Posted 31 May 2005 - 05:57 PM

QUOTE(tupacshakur @ May 31 2005, 06:53 PM)
QUOTE(Pooch @ May 31 2005, 05:51 PM)
There was one about some trout farming type chap adding limestone to his loch to increase the pH, it went from four to six. Then it asked you something about the conc. of H+ ions. It was increasing or decreasing by a factor of either two or one hundred, can anyone remember their answer?

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decreased by factor of 100

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I said that too. it is right because its in one of the pastpapers.

#234 YIC

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Posted 31 May 2005 - 05:57 PM

QUOTE(tupacshakur @ May 31 2005, 06:50 PM)
QUOTE(YIC @ May 31 2005, 05:49 PM)

Yea, I think now I can kinda remember as I am sure I used the phrase "end-point of the reaction". However, I am sure the question was a bit more complicated rather than why the starch was used. I understand though as no one has the papr in front of them laugh.gif

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is it ok to say it showed a better colour change?

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Don't worry. No need to take my word because my answer could have been wrong. In the marking instructions they say that markers should "look for reasons to give canditates marks rather than not give give them marks" - they also said that full credit should be given even if it is not completely correct, but shows good chemistry.

Here is the thing:

"A guiding principle in marking is to give credit for (partially) correct chemistry rather than to look for reasons not to give marks.

Example 1: The structure of a hydrocarbon found in petrol is shown below.
Name the hydrocarbon.

Although the punctuation is not correct, '3, methyl-hexane' should gain the full
mark.

Example 2: A student measured the pH of four carboxylic acids to find out how their strength is related to the number of chlorine atoms in the molecule. The results are shown.

Structural formula pH
CH3COOH 1·65
CH2ClCOOH 1·27
CHCl2COOH 0·90
CCl3COOH 0·51

How is the strength of the acids related to the number of chlorine atoms in the
molecule?

Although not completely correct, an answer such as 'the more Cl2, the stronger the
acid' should gain the full mark. "

#235 sai

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Posted 31 May 2005 - 05:58 PM

good old past papers...... biggrin.gif

#236 Soph.E.

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Posted 31 May 2005 - 05:59 PM

Copper does react with acids... doesn't it? Why wouldn't it - it's a metal even if it is relatively unreactive!

#237 bred

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Posted 31 May 2005 - 05:59 PM

QUOTE(e-unit @ May 31 2005, 06:55 PM)
But copper doesnt react with acids so it was only co2

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Oh, I think I realise what question we're on about now. I think I assumed the Cu(s) did not react.
Unless someone could post the precise question I think I'm at a loss to really remember it.
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#238 e-unit

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Posted 31 May 2005 - 06:03 PM

QUOTE(Soph.E. @ May 31 2005, 06:59 PM)
Copper does react with acids... doesn't it? Why wouldn't it - it's a metal even if it is relatively unreactive!

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The equation is actually:
acid + reactive metal -------> Salt + Hydrogen

#239 YIC

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Posted 31 May 2005 - 06:03 PM

For that question with the mask and why the CO2 would disappear, what did people put? I spoke some garbage about the CO2 dissolving in water vapour to produce carbonic acid which would neutralise the potassium hydroxide. Even though nothing was in solution I said that the water vapour would consense.

#240 e-unit

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Posted 31 May 2005 - 06:03 PM

QUOTE(YIC @ May 31 2005, 07:03 PM)
For that question with the mask and why the CO2 would disappear, what did people put? I spoke some garbage about the CO2 dissolving in water vapour to produce carbonic acid which would neutralise the potassium hydroxide. Even though nothing was in solution I said that the water vapour would consense.

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KOH was produced which absorbs CO2





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