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Which mixture of water and H2SO4 represents a solution with a concentration that is...

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saj-94 | (Level 1) Salutatorian

Posted September 6, 2013 at 2:51 PM via web

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Which mixture of water and H2SO4 represents a solution with a concentration that is closest to 30% by mass H2SO4?  
(A)  30 g H2SO4 + 100 g H2O
(B)  1 mol H2SO4 + 200 g H2O
(C)  30 mol H2SO4 + 0.70 kg H2O
(D)  0.30 mol H2SO4 + 0.70 mol H2O

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justaguide | College Teacher | (Level 2) Distinguished Educator

Posted September 6, 2013 at 3:23 PM (Answer #1)

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The molar mass of H2SO4 is 98.079 g/mole and the molar mass of water is 18 g/mole.

For the given choices, the concentration of H2SO4 by mass is:

(A)  30 g H2SO4 + 100 g H2O: 30/130 `~~` 0.23

(B)  1 mole H2SO4 + 200 g H2O : 98/(98 + 200) `~~` 0.32

(C)  30 mole H2SO4 + 0.70 kg H2O : (30*98)/(700+30*98) `~~` 0.80

(D)  0.30 mole H2SO4 + 0.70 mole H2O : (0.3*98)/(0.3*98+0.7*18) `~~` 0.7

The value closest to 30% by mass of H2SO4 is given by option B.

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