ALL QUESTIONS ANSWERED PLEASE Which of the following liquid systems would be exp

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ALL QUESTIONS ANSWERED PLEASE

Which of the following liquid systems would be expected to have the lowest vapor pressure at room temperature? a 1.00 m solution of ethanol in water a 1.00 m solution of sucrose in water a 1.00 m solution of acetone (CH_3C(O)CH_3) in water a 1.00 m solution of NaCl in water all are the same A 10.0% by weight solution of NaCl in water has a modality of: 0.127 m 1.42 m 1.50 m 7.85 m impossible to determine unless you know the density of the solution If freezing point depression was used to determine the molecular weight of a strong add dissolved in water, and the dissociation of the add wasn't taken into account, the determined value of the molecular weight of the add would be: accurate too high too low inaccurate, but in a direction that cannot be predicted

Explanation / Answer

11) Step 1: Calculate the moles of NaCl in 10.0 g   of    NaCl.

                       n = g/mm
                          = 10.0g / 58.5 g/mol
                          = 0.171 mol of NaCl.

Step 2: Calculate the kilograms of H2O in 100 grams of this solution. (Remember it is grams of solution with percent concentration, but kilograms (or 1000 g) of solvent with molality.

There is 10.0 grams of NaCl in 100.0 grams of solution. So there must be 100.0 g - 10.0 g = 90.0 grams of water present. 90.0 grams = 0.090 kg of water.

Step 3: Calculate molality, m, the ratio of moles to kg of solvent.

m = moles of solute / kg of solvent
    = 0.171 mol of NaCl / 0.090 kg of H2O
    = 1.90 m

Therefore a 10.0% w/w NaCl solution is also 1.90 m NaCl

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