Chemistry Lab C

[kenniky]

Do sig figs matter?

Yes! I haven't ever encountered anything in Chemistry where sig figs don't matter, whether or not it's Science Olympiad. Usually in the instructions of your test, it will tell you whether or not they matter, but always just assume they matter, just in case. It's a sad day when you get answers right but they don't have the right number of sig figs.

To add on, if they don't specify, always give at least three sig figs

[Eureka314]

What sorts questions about physical properties would appear on tests? Would there be calculations or things like differentiating physical from chemical properties?

[Nerd_Bunny]

What sorts questions about physical properties would appear on tests? Would there be calculations or things like differentiating physical from chemical properties?

There will definitely be calculations. Practice calculating molarity, molality, and freezing point depression to start out with. Others will be needed, but that's what I've started out with. There really aren't many resources here or on the wiki because physical properties hasn't been a topic since 2006.

[Nerd_Bunny]

Just curious...what are the topics next year for Chem Lab? I know one is going to be physical properties, but what about the other one?

[Unome]

Just curious...what are the topics next year for Chem Lab? I know one is going to be physical properties, but what about the other one?

Chem Lab is hard to predict because we've yet to actually go through a full cycle of topics. My bet is on Acids and Bases or Aqueous Solutions, though I think the former is more likely.

[Nerd_Bunny]

I'm having trouble with this Molarity problem and I was wondering if someone could help me figure out where I went wrong. I haven't done these in a while so i'm wondering if I just forgot a step...

Problem: A sample of HCl is brought into a laboratory and mixed with an equal volume of a preservative solution. For analysis, a 5.00 mL sample of this new solution is diluted to 100 mL with water, and the concentration of chloride ions in the diluted solution is found to be 3.0 * 10^-3 M. What is the chloride concentration of the original sample brought into the laboratory.

Using M1*V1 = M2*V2, I got 6.0 * 10^-2. According to the answer key, the correct answer is 1.2 * 10^-1. I can't figure out where I went wrong.

M1 * 5.00 = [3.0 * 10^-3] * 100

M1 * 5.00 = 0.3

M1 = 6.0 * 10^-2

Is there another step?

[kenniky]

I'm having trouble with this Molarity problem and I was wondering if someone could help me figure out where I went wrong. I haven't done these in a while so i'm wondering if I just forgot a step...

Problem: A sample of HCl is brought into a laboratory and mixed with an equal volume of a preservative solution. For analysis, a 5.00 mL sample of this new solution is diluted to 100 mL with water, and the concentration of chloride ions in the diluted solution is found to be 3.0 * 10^-3 M. What is the chloride concentration of the original sample brought into the laboratory.

Using M1*V1 = M2*V2, I got 6.0 * 10^-2. According to the answer key, the correct answer is 1.2 * 10^-1. I can't figure out where I went wrong.

M1 * 5.00 = [3.0 * 10^-3] * 100

M1 * 5.00 = 0.3

M1 = 6.0 * 10^-2

Is there another step?

It's telling that the answer is 2x what you got but I can't figure out where you went wrong either... maybe it's an error? Not sure

[dmis]

I'm having trouble with this Molarity problem and I was wondering if someone could help me figure out where I went wrong. I haven't done these in a while so i'm wondering if I just forgot a step...

Problem: A sample of HCl is brought into a laboratory and mixed with an equal volume of a preservative solution. For analysis, a 5.00 mL sample of this new solution is diluted to 100 mL with water, and the concentration of chloride ions in the diluted solution is found to be 3.0 * 10^-3 M. What is the chloride concentration of the original sample brought into the laboratory.

Using M1*V1 = M2*V2, I got 6.0 * 10^-2. According to the answer key, the correct answer is 1.2 * 10^-1. I can't figure out where I went wrong.

M1 * 5.00 = [3.0 * 10^-3] * 100

M1 * 5.00 = 0.3

M1 = 6.0 * 10^-2

Is there another step?

It's telling that the answer is 2x what you got but I can't figure out where you went wrong either... maybe it's an error? Not sure

I think I found the error. You solved the concentration of cl- ions in the new solution (the acid mixed with the preservative solution). The question asks for the concentration of the original hcl solution, which is diluted to double the volume when it is mixed with he preservative.

[Nerd_Bunny]

I'm having trouble with this Molarity problem and I was wondering if someone could help me figure out where I went wrong. I haven't done these in a while so i'm wondering if I just forgot a step...

Problem: A sample of HCl is brought into a laboratory and mixed with an equal volume of a preservative solution. For analysis, a 5.00 mL sample of this new solution is diluted to 100 mL with water, and the concentration of chloride ions in the diluted solution is found to be 3.0 * 10^-3 M. What is the chloride concentration of the original sample brought into the laboratory.

Using M1*V1 = M2*V2, I got 6.0 * 10^-2. According to the answer key, the correct answer is 1.2 * 10^-1. I can't figure out where I went wrong.

M1 * 5.00 = [3.0 * 10^-3] * 100

M1 * 5.00 = 0.3

M1 = 6.0 * 10^-2

Is there another step?

It's telling that the answer is 2x what you got but I can't figure out where you went wrong either... maybe it's an error? Not sure

I think I found the error. You solved the concentration of cl- ions in the new solution (the acid mixed with the preservative solution). The question asks for the concentration of the original hcl solution, which is diluted to double the volume when it is mixed with he preservative.

Ah, I see it now. Thanks!

[kenniky]

I'm having trouble with this Molarity problem and I was wondering if someone could help me figure out where I went wrong. I haven't done these in a while so i'm wondering if I just forgot a step...

Problem: A sample of HCl is brought into a laboratory and mixed with an equal volume of a preservative solution. For analysis, a 5.00 mL sample of this new solution is diluted to 100 mL with water, and the concentration of chloride ions in the diluted solution is found to be 3.0 * 10^-3 M. What is the chloride concentration of the original sample brought into the laboratory.

Using M1*V1 = M2*V2, I got 6.0 * 10^-2. According to the answer key, the correct answer is 1.2 * 10^-1. I can't figure out where I went wrong.

M1 * 5.00 = [3.0 * 10^-3] * 100

M1 * 5.00 = 0.3

M1 = 6.0 * 10^-2

Is there another step?

It's telling that the answer is 2x what you got but I can't figure out where you went wrong either... maybe it's an error? Not sure

I think I found the error. You solved the concentration of cl- ions in the new solution (the acid mixed with the preservative solution). The question asks for the concentration of the original hcl solution, which is diluted to double the volume when it is mixed with he preservative.

The question asks for the chloride concentration which could be taken to mean the chloride ions or the chloride as a whole.

Seems like a somewhat badly worded question