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Chapter 13: Problem 11

Define these concentration terms and give their units: percent by mass, molarity, molality. Compare their advantages and disadvantages.

Short Answer

Expert verified
Percent by mass measures the mass of solute per 100 units of the total solution's mass and doesn't change with temperature, but can be difficult to measure for gases. Its unit is percent (%). Molarity measures the number of solute's moles per solution's liter. It's commonly used and easy to measure, but changes significantly with temperature. Its unit is moles per liter (M or mol/L). Molality measures the number of solute's moles per solvent's kilogram, and doesn't change with temperature, but requires precise knowledge of the solution's components. Its unit is moles per kilogram (m or mol/kg).

Step by step solution

01

Define Percent by Mass

Percent by mass (also known as mass percent) is a measure of the mass of solute per 100 units of the total mass of the solution (solute and solvent together). The unit for this term is percent (%). It has several advantages, including that it does not change with temperature and that it's straightforward to understand. However, since mass is required, it can be difficult to measure for gases, and when the solute and solvent have approximately the same mass, small measurement errors can lead to large changes in calculated values.
02

Define Molarity

Molarity is the number of moles of solute per liter of solution. It's measured in moles per liter (M or mol/L). The main advantage is that molarity is commonly used and easy to measure, especially in laboratory settings. However, one of its major drawbacks is that volume (and hence molarity) changes significantly with temperature, which can make it less reliable.
03

Define Molality

Molality is the number of moles of solute per kilogram of solvent. The unit of measurement for this term is moles per kilogram (m or mol/kg), which offers the advantage of not changing with temperature, because it uses mass instead of volume. However, it requires more precise knowledge of the components of the solution, and it can be less practical to use, because the solvent's mass instead of the solution's volume is required.

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Most popular questions from this chapter

The molar mass of benzoic acid \(\left(\mathrm{C}_{6} \mathrm{H}_{5} \mathrm{COOH}\right)\) determined by measuring the freezing-point depression in benzene is twice that expected for the molecular formula, \(\mathrm{C}_{7} \mathrm{H}_{6} \mathrm{O}_{2}\). Explain this apparent anomaly.

Give two examples of a volatile liquid and two examples of a nonvolatile liquid.

A student is observing two beakers of water. One beaker is heated to \(30^{\circ} \mathrm{C},\) and the other is heated to \(100^{\circ} \mathrm{C}\). In each case, bubbles form in the water. Are these bubbles of the same origin? Explain.

A mixture of liquids \(A\) and \(B\) exhibits ideal behavior. At \(84^{\circ} \mathrm{C},\) the total vapor pressure of a solution containing 1.2 moles of \(A\) and 2,3 moles of \(B\) is 331 \(\mathrm{mmHg}\). Upon the addition of another mole of \(\mathrm{B}\) to the solution, the vapor pressure increases to 347 \(\mathrm{mmHg}\). Calculate the vapor pressures of pure \(\mathrm{A}\) and \(\mathrm{B}\) at \(84^{\circ} \mathrm{C}\)

Write the equation relating osmotic pressure to the concentration of a solution. Define all the terms and give their units.
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