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question on fundamentals G

Posted: Mon Apr 09, 2018 8:39 pm
by yazminedesan1F
Hey! I'm not very sure how to go about this question G.5:
A student prepared a solution of sodium carbonate by adding 2.111 g of the solid to a 250.0-mL volumetric flask and adding water to the mark. Some of this solution was transferred to a buret. What volume of solution should the student transfer into a fl ask to obtain (a) 2.15 mmol Na; (b) 4.98 mmol CO32; (c) 50.0 mg Na2CO3?

Re: question on fundamentals G

Posted: Mon Apr 09, 2018 9:29 pm
by Jocelyn Fermin1J
Hello, with help this is what we came up with:
Find the molarity of Na2CO3=0.08 M
convert mmol of Na+ to moles and convert mmol of CO3^2- and convert mmol of Na2CO3 to moles
mol of Na+/2(0.08M)
mol of CO3^2-/(0.8M)
mol of Na2C03/(0.8M)
convert answers to ML

Re: question on fundamentals G

Posted: Wed Apr 11, 2018 9:02 pm
by jessicasam
First, you need to find the molarity of Na2CO3

M=n/V= (2.11gNaCO3mol/105.951g)/.25L = .08 molL-1

Then you can solve each equation for a volume

a) V= 2.15x10-3 mol Na+ x 1 mol Na2C03 / .08 molNa2CO3 L-1 x 2mol Na+ = 1.35x 10-2L

b) V= 4.98x10-3 mol CO3 x 1 mol Na2C03 / .08 molNa2CO3 L-1 x 2mol CO3 = 6.3 x10-2L

c) V= .5g Na2CO3/ 105.951gmol-1NaCO3 x .08 molL-1 = 5.9 x10-3L

Re: question on fundamentals G

Posted: Sun May 06, 2018 3:09 pm
by Aryana Nazem 1A
Hey I was wondering if anyone could explain G.25 for me? I don't understand how to go about this, thanks in advance!!

G.25 Practitioners of the branch of alternative medicine known as homeopathy claim that very dilute solutions of substances can have an effect. Is the claim plausible? To explore this question, suppose that you prepare a solution of a supposedly active substance, X, with a molarity of 0.10 mol L 1. Then
you dilute 10. mL of that solution by doubling the volume, doubling it again, and so on, for 90 doublings in all. How many molecules of X will be present in 10. mL of the nal solution? Comment on the possible health bene ts of the solution.

Re: question on fundamentals G

Posted: Sun May 06, 2018 3:28 pm
by Chem_Mod
You need to think about what would happen if you continue to dilute your solution by half infinitely many times. The question you would have to answer is will you have any substance X left in your solution if you repeatedly diluted the solution that your infinitely diluted solution has some activity left

Re: question on fundamentals G

Posted: Sun May 06, 2018 8:30 pm
by Aryana Nazem 1A
So basically if I understand this right, we would only be expected to know that after many dilutions you would have close to less than one molecule left? If that is right, would we have to show some sort of mathematical work for this?