Can't Judge a Powder B

Re: Can't Judge a Powder B

Postby haven chuck on Wed May 26, 2010 9:48 pm

melody2k6 wrote:We don't have the test packet.

This wasn't on the test this year, but here is what they wanted in '06-
Put a set amount of the powder in a beaker and weigh it. Leave it alone for at least 15 minutes and then weigh it again. If there is a change is weight, then it is likely hygroscopic; if not, then it isn't. However, this process can take a fair amount of time if you have a shared triple beam balance (when you have so little time to start with), so it is probably worth considering just writing down something to the effect of "The powder clumps". This simple would receive AT LEAST 3-4 points anywhere, though most Invitational/Regional/State supervisors would probably give it 5, and would take far less time.
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Re: Can't Judge a Powder B

Postby ichaelm on Wed May 26, 2010 10:05 pm

Hmm. We just did clumping as an observation, and then we would test to see if it was hydrophobic by seeing if water made it wet when a drop was put on it. We would write "the powder does/does not adsorb to water." Note that "adsorb" is not a typo! :D
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Re: Can't Judge a Powder B

Postby 2win on Sat May 29, 2010 11:56 pm

melody2k6 wrote:
r00ki316 wrote:Please tell me I don't have to police you on the boards, Brian.


I think there's a rule against using real names on Scioly. Give Brian a break! Meanwhile, you should realize that it's very coincidental that Solon asked a question about hygroscopic-ness...


Um, not to be mean or anything, but please refrain from posting non-related comments on study/building threads. You could always use PM's.
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Re: Can't Judge a Powder B

Postby melody2k6 on Sun May 30, 2010 12:14 am

2win wrote:
melody2k6 wrote:
r00ki316 wrote:Please tell me I don't have to police you on the boards, Brian.


I think there's a rule against using real names on Scioly. Give Brian a break! Meanwhile, you should realize that it's very coincidental that Solon asked a question about hygroscopic-ness...


Um, not to be mean or anything, but please refrain from posting non-related comments on study/building threads. You could always use PM's.


Sorry. I have terrible judgement of simple things like that. Did anyone understand the question about the rotten egg odor? My partner and I had no idea what it meant.
Last edited by melody2k6 on Sun May 30, 2010 12:45 am, edited 1 time in total.
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Re: Can't Judge a Powder B

Postby robotman on Sun May 30, 2010 12:17 am

melody2k6 wrote:

Sorry. Did anyone understand the question about the rotten egg odor? My partner and I had no idea what it meant.

I think My partner and I did.
It was the Feric something (brownish color) that had the rotten egg odor
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Re: Can't Judge a Powder B

Postby melody2k6 on Sun May 30, 2010 12:20 am

robotman09 wrote:
melody2k6 wrote:

Sorry. Did anyone understand the question about the rotten egg odor? My partner and I had no idea what it meant.

I think My partner and I did.
It was the Feric something (brownish color) that had the rotten egg odor


Did it ask for something else though? I thought the question asked something about another observation we can make about Ferric Nitrate (I think. Not sure though)
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Re: Can't Judge a Powder B

Postby frogzorz on Sun May 30, 2010 10:07 am

Hmm. My partner and I concluded that it was the sodium sulfide. After all, sodium sulfide (Na2S) contains 2 molecules of sulfur, even in its hydrate form. Both the compound and its hydrate emit hydrogen sulfide, which smells like rotten eggs.
BTW, what the heck is ferric acid? The reactioms to it were similar to HCl except for a few.
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Re: Can't Judge a Powder B

Postby starpug on Sun May 30, 2010 10:59 am

frogzorz wrote:Hmm. My partner and I concluded that it was the sodium sulfide. After all, sodium sulfide (Na2S) contains 2 molecules of sulfur, even in its hydrate form. Both the compound and its hydrate emit hydrogen sulfide, which smells like rotten eggs.
BTW, what the heck is ferric acid? The reactioms to it were similar to HCl except for a few.

How does Sodium Sulfide have 2 molecules of sulfur when the charge on sulfur anion is -2 and the charge on the sodium cation is +1.
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Re: Can't Judge a Powder B

Postby rocketman1555 on Sun May 30, 2010 1:21 pm

frogzorz wrote:Hmm. My partner and I concluded that it was the sodium sulfide. After all, sodium sulfide (Na2S) contains 2 molecules of sulfur, even in its hydrate form. Both the compound and its hydrate emit hydrogen sulfide, which smells like rotten eggs.
BTW, what the heck is ferric acid? The reactioms to it were similar to HCl except for a few.


Sodium sulfide only has one molecule of sulfur, it has two molecules of sodium though.

And Ferric Acid is a weak acid, I don't know much else about it though.
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Re: Can't Judge a Powder B

Postby frogzorz on Sun May 30, 2010 1:42 pm

Oops. My bad. I thought it had two sulfur molecules. I hate my partner!! :evil:
A weak acid? We tested for a pH of 1 or 2.
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Re: Can't Judge a Powder B

Postby frogzorz on Sun May 30, 2010 1:44 pm

starpug wrote:
frogzorz wrote:Hmm. My partner and I concluded that it was the sodium sulfide. After all, sodium sulfide (Na2S) contains 2 molecules of sulfur, even in its hydrate form. Both the compound and its hydrate emit hydrogen sulfide, which smells like rotten eggs.
BTW, what the heck is ferric acid? The reactioms to it were similar to HCl except for a few.

How does Sodium Sulfide have 2 molecules of sulfur when the charge on sulfur anion is -2 and the charge on the sodium cation is +1.

Yeah, my partner didn't really explain to me the anion or the cation charges for Na2S. Or ichaelm. :|
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Re: Can't Judge a Powder B

Postby starpug on Sun May 30, 2010 1:56 pm

frogzorz wrote:Oops. My bad. I thought it had two sulfur molecules. I hate my partner!! :evil:
A weak acid? We tested for a pH of 1 or 2.

It's a common mistake

Also the term "weak acid" doesn't mean it can't have a ph of 1 or 2. pH is a measure of H+ ion concentration, so a saturated solution of say citric acid (what makes lemons so sour) can have a pH as low as or lower then a dilute solution of HCl. What makes HCl and other strong acids strong is that they completely dissociate in water so if you were to add the same number of moles of HCl and citric acid to water, the HCl would have the higher pH. The HCl would donate more H+ ions to the solution then the citric acid (making more Hydronium Ions, but the difference between H+ and H30+ is irrelvant to what I'm saying.) which makes the pH lower (they're inversely proportional since pH is the -log[H+]). Even among weak acids, some are stronger then others because some dissociate better then others. Also, pH paper has a history of being unreliable, so it's possible that was a faulty reading.

Ferric Acid's formula H2FeO4, I can't seem to find it's dissociation constant so I don't know how strong of a weak acid it is.
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Re: Can't Judge a Powder B

Postby haven chuck on Sun May 30, 2010 1:58 pm

melody2k6 wrote:
robotman09 wrote:
melody2k6 wrote:

Sorry. Did anyone understand the question about the rotten egg odor? My partner and I had no idea what it meant.

I think My partner and I did.
It was the Feric something (brownish color) that had the rotten egg odor


Did it ask for something else though? I thought the question asked something about another observation we can make about Ferric Nitrate (I think. Not sure though)


Yeah, the question was like "Besides a rotten egg odor, what did you observe when ferric nitrate was mixed with the powder". We figured they just wanted a solubility observation :|
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Re: Can't Judge a Powder B

Postby melody2k6 on Sun May 30, 2010 2:04 pm

starpug wrote:
frogzorz wrote:Oops. My bad. I thought it had two sulfur molecules. I hate my partner!! :evil:
A weak acid? We tested for a pH of 1 or 2.

It's a common mistake

Also the term "weak acid" doesn't mean it can't have a ph of 1 or 2. pH is a measure of H+ ion concentration, so a saturated solution of say citric acid (what makes lemons so sour) can have a pH as low as or lower then a dilute solution of HCl. What makes HCl and other strong acids strong is that they completely dissociate in water so if you were to add the same number of moles of HCl and citric acid to water, the HCl would have the higher pH. The HCl would donate more H+ ions to the solution then the citric acid (making more Hydronium Ions, but the difference between H+ and H30+ is irrelvant to what I'm saying.) which makes the pH lower (they're inversely proportional since pH is the -log[H+]). Even among weak acids, some are stronger then others because some dissociate better then others. Also, pH paper has a history of being unreliable, so it's possible that was a faulty reading.

Ferric Acid's formula H2FeO4, I can't seem to find it's dissociation constant so I don't know how strong of a weak acid it is.


I have always thought a weak acid meant an acid with a pH close to neutral. When my partner and I tested the pH of Ferric Acid (or whatever it is) we got a pH of 4. Would that be considered a weak acid?
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Re: Can't Judge a Powder B

Postby melody2k6 on Sun May 30, 2010 2:06 pm

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