Concept explainers
Estimate the osmotic pressure, freezing point, and boiling point of seawater, which you can approximate as equivalent to a
Interpretation:
The osmotic pressure, freezing point, and boiling point of seawater are to be estimated. The value of
Concept introduction:
Colligative properties are those properties of a material that depends on the number of particles of the substance present in material. The colligative properties are lowering of vapor pressure, elevation in boiling point, depression in freezing point and osmotic pressure.
Answer to Problem 7.72E
The osmotic pressure, freezing point, and boiling point of seawater are
Explanation of Solution
The molality of the seawater is
It is assumed that sea water only consists of water and sodium chloride.
The enthalpy of fusion of water is
The enthalpy of vaporization of water is
The molar mass of the water is
The boiling point of water is
The freezing point of water is
The sodium chloride salt gets dissociated in water to from sodium ion and chloride ion. Therefore, the number of particles into which sodium chloride is dissociated is
The formula of boiling point elevation constant is represented as,
Where,
•
•
•
•
Substitute the value of
The formula for elevation in boiling point is given as,
Where,
•
•
•
•
•
Rearrange the equation for the value of
Substitute the value of,
The boiling point of the seawater in Kelvin is represented as,
Therefore, the boiling point of the seawater is
The formula of freezing point depression constant is represented as,
Where,
•
•
•
•
Substitute the value of
The formula for depression in freezing point is given as,
Where,
•
•
•
•
Rearrange the equation for the value of
Substitute the value of
The freezing point of the seawater in Kelvin is represented as,
Therefore, the freezing point of the seawater is
The relation between mole fraction of a solute and molarity of the solution is given as,
Where,
•
•
•
Rearrange the equation for the value of
Substitute the value of molarity of seawater and molar mass of water in the above equation.
Molar volume of the water at standard temperature is
The standard temperature is
The osmotic pressure of the solution is given as,
Where,
•
•
•
Substitute the value of
The osmotic pressure of the seawater is
The osmotic pressure, freezing point, and boiling point of seawater are
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Chapter 7 Solutions
Physical Chemistry
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