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Answers to 2007 Higher Chemistry - HSN forum - Page 2

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Answers to 2007 Higher Chemistry


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#21 Cooldude

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Posted 31 May 2007 - 10:20 AM

yaaayyy biggrin.gif i think i got about 82%!! should be an A ...... biggrin.gif

#22 iain3915

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Posted 31 May 2007 - 11:19 AM

Are you certain about your answer to multiple choice 13; How many moles of oxygen atoms are in 0.5 mol of carbon dioxide?

You answered C - 1 Mole

I think 0.5 mol....but I'm just a student.

#23 jackbauer

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Posted 31 May 2007 - 12:03 PM

QUOTE(ginneswatson @ May 30 2007, 06:24 AM) View Post
QUOTE(Kiltox @ May 30 2007, 12:37 AM) View Post
Think I've lost more marks in the multiple choice than in the rest but nothing too major so should hopefully do well biggrin.gif Thanks for that, though I'm not gonna look into it in too much detail, will no doubt cause paranoia.

I think you've made a mistake on one of the MC questions though, the one that asks you to compare sodium hydroxide to ammonia.

Surely NaOH has a higher pH as well as a higher conductivity since it's a strong base and the other is weak? smile.gif



ohmy.gif Your absolutely right. The correct answer to Q36 is B. Sorry about that. rolleyes.gif


hi,

can someone please explain how Q36 can be B?

surely with a high pH, like 13, there are less H+ ions and more OH- ions, and it is the amount of H+ ions present that determine conductivity, ie the greaer the amount of H+ ions the greater the conductivity, and low pH (like 2) has a greater conductivity than 10?

so i thought Q36) would be A?

i'm confused is all. unsure.gif

cheers

#24 englisher

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Posted 31 May 2007 - 03:38 PM

QUOTE(iain3915 @ May 31 2007, 12:19 PM) View Post
Are you certain about your answer to multiple choice 13; How many moles of oxygen atoms are in 0.5 mol of carbon dioxide?

You answered C - 1 Mole

I think 0.5 mol....but I'm just a student.



Hi there.

The formula for carbon dioxide is CO2. So there are two oxygens for every one carbon. There are, therefore, 2 moles of oxygen for every mole of carbon dioxide. And 1 mole of Oxygen for every 0.5moles of carbon dioxide.

QUOTE(jackbauer @ May 31 2007, 01:03 PM) View Post
QUOTE(ginneswatson @ May 30 2007, 06:24 AM) View Post
QUOTE(Kiltox @ May 30 2007, 12:37 AM) View Post
Think I've lost more marks in the multiple choice than in the rest but nothing too major so should hopefully do well biggrin.gif Thanks for that, though I'm not gonna look into it in too much detail, will no doubt cause paranoia.

I think you've made a mistake on one of the MC questions though, the one that asks you to compare sodium hydroxide to ammonia.

Surely NaOH has a higher pH as well as a higher conductivity since it's a strong base and the other is weak? smile.gif



ohmy.gif Your absolutely right. The correct answer to Q36 is B. Sorry about that. rolleyes.gif


hi,

can someone please explain how Q36 can be B?

surely with a high pH, like 13, there are less H+ ions and more OH- ions, and it is the amount of H+ ions present that determine conductivity, ie the greaer the amount of H+ ions the greater the conductivity, and low pH (like 2) has a greater conductivity than 10?

so i thought Q36) would be A?

i'm confused is all. unsure.gif

cheers


It's because more of the H2O molecules have dissociated into H+ and OH- ions and so there are more charge carriers (hence conductivity increases). I may be wrong though.

#25 jackbauer

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Posted 31 May 2007 - 03:52 PM

QUOTE(englisher @ May 31 2007, 04:38 PM) View Post
It's because more of the H2O molecules have dissociated into H+ and OH- ions and so there are more charge carriers (hence conductivity increases). I may be wrong though.


Do you mean OH- carry charges/electrons/electricity as well as H+ ions?

I thought it was only H+ ions that carried electricity. I may be wrong though. unsure.gif

#26 Cooldude

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Posted 31 May 2007 - 04:04 PM

i think it's just ions in general, positive or negative....i also could be wrong though!! tongue.gif

#27 ginneswatson

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Posted 31 May 2007 - 05:19 PM

QUOTE(Lizzie @ May 31 2007, 05:04 PM) View Post
i think it's just ions in general, positive or negative....i also could be wrong though!! tongue.gif


Any and every ionic compound conducts. H+ ions are the best conductors, followed by OH ions, followed by all the rest, in the ratio 10:5:1 if I remember correctly.

wink.gif

#28 jackbauer

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Posted 31 May 2007 - 05:33 PM

QUOTE(ginneswatson @ May 31 2007, 06:19 PM) View Post
QUOTE(Lizzie @ May 31 2007, 05:04 PM) View Post
i think it's just ions in general, positive or negative....i also could be wrong though!! tongue.gif


Any and every ionic compound conducts. H+ ions are the best conductors, followed by OH ions, followed by all the rest, in the ratio 10:5:1 if I remember correctly.

wink.gif


cheers ginneswatson cool.gif

#29 englisher

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Posted 31 May 2007 - 06:28 PM

By the way thanks for the answers (especially so quickly) and all the help in the lead up to the exam, ginneswatson. thumbsup.gif

#30 iain3915

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Posted 31 May 2007 - 08:06 PM

QUOTE(englisher @ May 31 2007, 04:38 PM) View Post
QUOTE(iain3915 @ May 31 2007, 12:19 PM) View Post
Are you certain about your answer to multiple choice 13; How many moles of oxygen atoms are in 0.5 mol of carbon dioxide?

You answered C - 1 Mole

I think 0.5 mol....but I'm just a student.



Hi there.

The formula for carbon dioxide is CO2. So there are two oxygens for every one carbon. There are, therefore, 2 moles of oxygen for every mole of carbon dioxide. And 1 mole of Oxygen for every 0.5moles of carbon dioxide.


Yes. But one mole of oxygen consists of 02 molecules since oxygen is diatomic. There are, therefore, 1 moles of oxygen for every 1 mole of carbon. Since you have 0.5 moles of CO2, this implies you have 0.5 moles of O2, surely.

Iain

#31 ginneswatson

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Posted 01 June 2007 - 06:22 AM

QUOTE(iain3915 @ May 31 2007, 09:06 PM) View Post
QUOTE(englisher @ May 31 2007, 04:38 PM) View Post
QUOTE(iain3915 @ May 31 2007, 12:19 PM) View Post
Are you certain about your answer to multiple choice 13; How many moles of oxygen atoms are in 0.5 mol of carbon dioxide?

You answered C - 1 Mole

I think 0.5 mol....but I'm just a student.



Hi there.

The formula for carbon dioxide is CO2. So there are two oxygens for every one carbon. There are, therefore, 2 moles of oxygen for every mole of carbon dioxide. And 1 mole of Oxygen for every 0.5moles of carbon dioxide.


Yes. But one mole of oxygen consists of 02 molecules since oxygen is diatomic. There are, therefore, 1 moles of oxygen for every 1 mole of carbon. Since you have 0.5 moles of CO2, this implies you have 0.5 moles of O2, surely.

Iain


Sorry Iain. You are confused. 'Oxygen' only = O2 when talking about the element, oxygen gas as it exists floating in the air. In a compound 'oxygen' can be any quantity, it is determined by what the oxygen is combined with.

The question was also quite specific in asking for moles of oxygen atoms.

examples: 1mole of Na2O = 0.5 mol of O atoms
1 mole of MgO = 1 mole of O atoms
1 mole of CO2 = 2 moles of O atoms, and so on.

wink.gif



#32 iain3915

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Posted 01 June 2007 - 12:02 PM

Ah ok. Thankyou. I should have read the "atoms" part.

#33 1oon85

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Posted 21 May 2008 - 08:23 PM

Is this completed paper still available? Just that I cant get it.





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