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March 25, 2017

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Nitric acid is commonly purchased as a 16 M solution, which has a density of 1.41 g/mL.
Convert this molarity to a) mass percentage, b) molality, c) mole fraction.

A) 16molHNO3(63.02HNO3/1MolHNO3)=1,008.32gHNO3
- 1,000gH20(1MolH20/1.41ml/g)=1410ml/mol
w/w= 1008.32/1410= 71.5%w/w

B)1410-1008.32= 401.88 --> 16molHNO3/401.32= 0.40m

C)71.5%w/w (1mol/63.02)= 1.13--> 1.13
100gSoln(1ml/1.41)= 70.92--> .113/.71= .16 mol frac

  • Chemistry - ,

    A and B are ok.
    I think C is incorrect.
    If the soln is 71.5%, then you are right that 1.13 mol HNO3.
    100 g soln = 71.5g HNO3 = 2.85g H2O (I think you converted to volume).
    Then XHNO3 = 1.13 mols HNO3/(1.13+2.85) = about 0.4 or so.

  • Chemistry - ,

    Dr.Bob,
    How did you obtain 2.85gH20?

  • Chemistry - ,

    I made two typos and did not show a step. Here it is in detail.
    That should be 100g total - 71.5g HNO3 = 28.5 H2O.
    mols H2O = 28.5/18 = 1.58
    total mols = 1.58 + 1.13 = 2.71
    XHNO3 = 1.13/2.71 = 0.417

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