Homework Help: Chemistry

Posted by Adam on Friday, January 28, 2011 at 12:00am.

Could someone help me with these problems;

A)If 5.97mL of a solution of NaCl contains 2.54g of sodium ion, what is the molarity of the sodium chloride solution?
-I know M=#moles solute/L
but when I do this I get 7.28*10^-3 which is wrong, the answer should be 1.85*10^-2

B) Combustion analysis of a 22.0-mg sample of the painkiller morphine produced 13.2 mg of water. What is the % by mass of hydrogen in morphine?

Chemistry - DrBob222, Friday, January 28, 2011 at 12:15am
If you had shown your work I could have found your error; however, I suspect the error you made was to divide 2.54 g by molar mass NaCl (about 58.5) whereas the problem states that it is 2.54 g of the Na^+. So 2.54/23 = moles NaCl.
There is a bigger problem than that. Could you have made a typo and the 2.54 g whould be 2.54 mg? If so then
2.54 mg/23 = ?? mmoles and ??mmoles/5.97 mL = 0.0185 M.
But if 2.54g is correct, then
2.54/23 = 0.110 moles and that divided by 0.00597 L = a number 100 x higher than the answer. Of course, that could be 5.97L too for the correct answer to be 0.0185M

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