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July 01, 2026, 07:13:01 pm
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Author Topic: more questions  (Read 26796 times)  Share 

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helen

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Re: more questions
« Reply #90 on: June 11, 2008, 11:59:04 am »
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can someone tell me the difference between chemical and physical properties and an example of them? like BT. is that physical?
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vce01

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Re: more questions
« Reply #91 on: June 11, 2008, 12:23:13 pm »
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a diol = when you have 2 hydroxyl groups, yeah?
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shinny

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Re: more questions
« Reply #92 on: June 11, 2008, 12:53:21 pm »
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Quote from: vce01 on June 11, 2008, 12:23:13 pm
a diol = when you have 2 hydroxyl groups, yeah?
yeh, something like HO-R-OH

Quote from: helen on June 11, 2008, 11:59:04 am
can someone tell me the difference between chemical and physical properties and an example of them? like BT. is that physical?
a chemical property is something that is evident from its reaction with other chemical compounds, whereas a physical property is its reaction with physical things such as heat; so yes BP and MP are physical. these arent exactly great definitions but it should make it a bit more clear. go wiki if u want the exact ones but these should make it clear enough
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monicak

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Re: more questions
« Reply #93 on: June 11, 2008, 12:56:05 pm »
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Just going through a few practice questions..
There is a pH question, which I think has an incorrect answer:
The pH of a 10^(-9) solution of HCl is closest to...
Thanks
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vce01

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Re: more questions
« Reply #94 on: June 11, 2008, 12:59:31 pm »
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Quote from: monicak on June 11, 2008, 12:56:05 pm
Just going through a few practice questions..
There is a pH question, which I think has an incorrect answer:
The pH of a 10^(-9) solution of HCl is closest to...
Thanks

isnt it 9?  :-\
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monicak

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Re: more questions
« Reply #95 on: June 11, 2008, 01:03:18 pm »
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Quote from: vce01 on June 11, 2008, 12:59:31 pm
isnt it 9?  :-\

That's what I though. but the answer is 7... Assume it's a typo?? :-\
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vce01

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Re: more questions
« Reply #96 on: June 11, 2008, 01:10:00 pm »
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Quote from: monicak on June 11, 2008, 01:03:18 pm
Quote from: vce01 on June 11, 2008, 12:59:31 pm
isnt it 9?  :-\

That's what I though. but the answer is 7... Assume it's a typo?? :-\


yeah should be, id get an answer from someone else too tho, could be a dodgy question..
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helen

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Re: more questions
« Reply #97 on: June 11, 2008, 01:21:43 pm »
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yeah! i was reading that question too! it HAS to be a typo because why in the world would HCl be neutral? unless...again...we're missing something here

omg. maybe because its 10^-9 but because Hcl has to be acidic then...maybe the closest thing it can be is neutral? ahahahaha now im making crap up! lol
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shinny

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Re: more questions
« Reply #98 on: June 11, 2008, 01:27:04 pm »
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whats the full question exactly? i cant see how its possible for a solution of HCl to be basic o_o i assume 10^-9 was the number of mols or something, not concentration?
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monicak

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Re: more questions
« Reply #99 on: June 11, 2008, 02:26:24 pm »
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Here's the full question:
The pH of a 10^(-9)M solution of HCl is closest to:
a) 4
b) 6
c) 7
d) 9
And the answer, on the answer sheet, is c...
« Last Edit: June 11, 2008, 02:34:00 pm by monicak »
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polky

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Re: more questions
« Reply #100 on: June 11, 2008, 02:28:44 pm »
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10^(-9) solution... there are no units for that number lol.

I would assume that it's 10^(-9)M and thus the answer would be d, but apparently not...

!!!THE POWER OF HYDROGEN!!!
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monicak

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Re: more questions
« Reply #101 on: June 11, 2008, 02:35:48 pm »
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Quote from: polky on June 11, 2008, 02:28:44 pm
10^(-9) solution... there are no units for that number lol.
Sorry, it is actually M.. fixed my original post
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shinny

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Re: more questions
« Reply #102 on: June 11, 2008, 02:48:39 pm »
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the pH rule seems to only apply up to [H+]=10^-7 because otherwise this wouldnt make any sense; u can't make a basic solution from adding HCl (i think, unless adding such minute amounts of H+ does something weird to the ionic product of water). i assume at such minute concentrations of HCl that u could pretty much consider the solution just almost equivalent to pure water (~7 pH)
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vce01

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Re: more questions
« Reply #103 on: June 11, 2008, 02:51:08 pm »
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Quote from: shinjitsuzx on June 11, 2008, 02:48:39 pm
the pH rule seems to only apply up to [H+]=10^-7 because otherwise this wouldnt make any sense; u can't make a basic solution from adding HCl (i think, unless adding such minute amounts of H+ does something weird to the ionic product of water). i assume at such minute concentrations of HCl that u could pretty much consider the solution just almost equivalent to pure water (~7 pH)

lol, genius. makes sense now
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vce01

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Re: more questions
« Reply #104 on: June 11, 2008, 03:51:33 pm »
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A soluble fertilister contains phosphorus in the form of phosphate ions. To determine the phosphate content by gravimetric analysis, 5.97 g of the fertiliser powder was completely dissolved in water to make a volume of 250.0 mL. A 20.00 mL volume of this solution was pipetted into a conical flask and the phosphate ions in the solution were precipitated as MgNH4PO4. The precipitate was filtered, washed with water and then converted by heating into Mg2P2O7. THe mass of it was 0.0352g.

If the conical flask had been previously washed with water but not dried, indicate the likely effect on the calculated percentage of phosphate ions in the fertiliser.

The answer says 'no effect on calculated result.' But, since there's water left over in the conical flask, wouldn't the concentration of phosphate be less than what I calculated, since I used 20 mL as my volume and the real volume is higher than that? Wouldn't the calculated result be too low?
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