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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?

Nerd_Bunny wrote: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

kenniky wrote:

Nerd_Bunny wrote: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.

dmis wrote:

kenniky wrote:

Nerd_Bunny wrote: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!

dmis wrote:

kenniky wrote:

Nerd_Bunny wrote: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

kenniky wrote:

dmis wrote:

kenniky wrote: 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

Yeah, I spent a long time trying to figure out what it meant.

I had a question for physical properties. When they are asking for the magnetism, will they be asking about paramagnetic vs diamagnetic or other topics?
also, for density and color, will we need a list of it in our cheat sheet or will they just be asking certain elements?

Thank You and a Happy New Year!!!

2017-18 Events:
Chemistry Lab, Material Science, Thermodynamics, Fermi Questions.

kenniky wrote:

Nerd_Bunny wrote:

geniusjohn5 wrote: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

Oh, I just did some research on this and my research points out that you should never give more sig figs than the lowest amount given to you. You give the amount of sig figs of the lowest value. For example, if you're doing a problem and the values you're given for certain things in the problem are 5.0, 139, and 55.2, then you need 2 sig figs in your final answer.

How is everyone studying for physical properties? Since this topic hasn't been in rotation for a while I'm having trouble finding any resources to help study.

Nerd_Bunny wrote:How is everyone studying for physical properties? Since this topic hasn't been in rotation for a while I'm having trouble finding any resources to help study.

The thing I have seen most is either a) identify, given a chart with common tests, which of these samples is which, or b) "a crystalline solid that is a poor conductor of electricity in solid state, dissolves and has a high melting point is likely to be which of the following (answer is ionic)."
for studying, i just put a chart on my cheat sheet since i know that i would probably get a lot of the stuff confused during competition. i also learned some exceptions, but i found it hard to study for this part of the test (other than also memorizing different physical properties)