Can't Judge a Powder B

[Cyrus_D]

Here's a question: How are you supposed to find the mass of something without a balance?

Its almost impossible.

[amerikestrel]

Here's a question: How are you supposed to find the mass of something without a balance?

Its almost impossible.

No... you can calculate the mass if you know the density and volume of the substance.

[2win]

but you don't. They gave us the powder in the container, and then told us to find the mass and density.

[Sunshine]

don't worry 2win, you weren't the only freaking out about that. I just guesstimated it, but in the end, those questions were crossed off.

[2win]

really? that's good. yeah, i guessed too. My coach said to just use something we had as a reference.

[Phenylethylamine]

I am also trying to find out about the use of Benidict's solution.

Benedict's solution tests for simple sugars (more specifically, reducing sugars- I don't know how much you know about carbohydrates, but there are monosaccharides made up of one sugar unit, disaccharides made up of two, and so on; most polysaccharides, made up of many units, aren't 'sugars' really- one example would be starch. Reducing sugars don't have to be monosaccharides; certain disaccharides, because of the way they are bonded, are also reducing). This includes monosaccharides such as glucose and fructose, and disaccharides such as lactose. Sucrose- table sugar- is not a reducing sugar and will not show up positive in Benedict's solution.

To test a substance with Benedict's solution, mix a small amount of the substance with the solution in a test tube, and place it in a hot water bath for anywhere from two to ten minutes, depending on how readily the sugar reduces (monosaccharides will react more quickly than reducing disaccharides). If reducing sugars are present, the solution will change color from blue to orange.

As you can see, this isn't the most practical test to do in competition, because it takes a long time. However, you can run it while you're conducting other tests, so it's not impossible; you just lose the more specific observation of approximately how long the solution took to change color if you're not watching it.

[gneissisnice]

I am also trying to find out about the use of Benidict's solution.

Benedict's solution tests for simple sugars (more specifically, reducing sugars- I don't know how much you know about carbohydrates, but there are monosaccharides made up of one sugar unit, disaccharides made up of two, and so on; most polysaccharides, made up of many units, aren't 'sugars' really- one example would be starch. Reducing sugars don't have to be monosaccharides; certain disaccharides, because of the way they are bonded, are also reducing). This includes monosaccharides such as glucose and fructose, and disaccharides such as lactose. Sucrose- table sugar- is not a reducing sugar and will not show up positive in Benedict's solution.

To test a substance with Benedict's solution, mix a small amount of the substance with the solution in a test tube, and place it in a hot water bath for anywhere from two to ten minutes, depending on how readily the sugar reduces (monosaccharides will react more quickly than reducing disaccharides). If reducing sugars are present, the solution will change color from blue to orange.

As you can see, this isn't the most practical test to do in competition, because it takes a long time. However, you can run it while you're conducting other tests, so it's not impossible; you just lose the more specific observation of approximately how long the solution took to change color if you're not watching it.

There's a very good chance you wont get Benedict's (or Fehlig's, basically the same thing) in CJAB. The chemicals I remember getting were NaOH, HCl, H2O (those are the standard ones, at every competition), phenolphthalein, and I think we got Bromothymyl Blue once, but Im not sure, and you might also get silver nitrate.

And by the way, one thing we had a problem with was how to tell if there were certain ions in the substance. If you know what to look for, you'll be able to tell, but note that the ions would go under inferences, so for observations, put down whatever makes you know that the ion is there, if that makes sense (i hope it does, i know it was really grammatically incorrect).

Here's a list of ions that I remember:

Carbonate (CO3 2-)-Present if the substance fizzes in HCl.
Chlorine (Cl-)-Present if it forms a yellow precipitate when added to Silver Nitrate (AgNO3)
Cyanide(CN-)- Present if it's acidic (which, now that I think about it, doesnt make sense, but that's what I remember when I was looking for a list for this years back).
Ammonium (NH3+)-Present if it smells like ammonia when you add NaOH (remember, waft so you dont get DQed).

And....that's all I remember. I coulda sworn I knew more than that, but I seem to have forgotten em all.

[HappySciencePie]

Wait.
So we DO have to identify them? D:

[amerikestrel]

Wait.
So we DO have to identify them? D:

No. You just have to say what traits they have.

[gneissisnice]

Wait.
So we DO have to identify them? D:

In your observations, you cant identify them directly. That would be an inference.
Instead, you need to write down how you identified it, so if they ask something like "Did it contain a carbonate ion?" you say Yes/No and put down the number of your observation that showed that the powder fizzes in HCl.
So you're writing down that it fizzes in acid, but you're using that observation to infer that it contains a carbonate ion.