
Concept explainers
(a)
Interpretation:
The mass of KCl required to get 100 mL of 2.0m of KCl in water needs to be determined, if density of water is 1.00 g/cm3
Concept Introduction:
The measure of concentration of solute in solution or the amount of substance that is present in a specified amount of mass of solvent is termed as Molality.
Molarity is the number of moles of solute per liter of solution. Most of the solution concentration is indicated in terms of Molarity as it will indicate the volume of solvent or amount of solute.
(a)

Answer to Problem 22E
For preparing 100 mL of 2.0 m KCl solution, it is necessary to dissolve 15 g in 100 ml water.
Explanation of Solution
Given density of water as 1.00 g/cm3
Volume of water 100 mL
To convert to kg, divide by 1000
Given molality of KCl as 2 m and to get molar mass,
As Molality is 2 m, it indicates 2 mol KCl in 1 kg of water i.e.
Molarity is 74.55 g is present in 1 mol KCl.
To compute the mass of KCl in 2m, multiply both with mass of solvent in kg
Therefore, to prepare 100 ml of 2m KCl solution, we require 15g of KCl in 100 mL of water.
(b)
Interpretation:
The mass of NaOH required to get 100 mL of 15% of NaOH in water needs to be determined, if density of water is 1.00 g/cm3
Concept Introduction:
The measure of concentration of solute in solution or the amount of substance that is present in a specified amount of mass of solvent is termed as Molality.
Molarity is the number of moles of solute per liter of solution. Most of the solution concentration is indicated in terms of Molarity as it will indicate the volume of solvent or amount of solute.
(b)

Answer to Problem 22E
To prepare 100 mL of 15% of NaOH in water, we require 18 grams of NaOH.
Explanation of Solution
Given density of water as 1.00 g/cm3
Volume of water 100 mL
Give mass percentage of NaOH as 15% which means 100g of solution contains 15 grams of NaOH solute.
Mass of NaOH solute =15g
Mass of solution = 100g
Hence, Mass of solution = Mass of NaOH solute + Mass of solvent
OR
Mass of solvent = Mass of solution − Mass of NaOH solute
= 100 g - 15g
= 85 g
In other words to prepare 15% NaOH solution by mass, 15g of NaOH solute is dissolved in 85 g of solvent.
In order to find out the mass of NaOH required to prepare 15% solution in 100 ml solvent, the mass of water is multiplied by mass percentage conversion factor:
Therefore, to prepare 100 mL of 15% NaOH solution, we need to dissolve 18g of NaOH in 100mL of water.
(c)
Interpretation:
The mass of NaOH required to get 100 mL of 25% of NaOH in CH3OH needs to be determined, if density of CH3OH is 0.79g/cm3.
Concept Introduction:
The measure of concentration of solute in solution or the amount of substance that is present in a specified amount of mass of solvent is termed as Molality.
Molarity is the number of moles of solute per liter of solution. Most of the solution concentration is indicated in terms of Molarity as it will indicate the volume of solvent or amount of solute.
(c)

Answer to Problem 22E
To prepare 100 mL of 25% of NaOH in CH3OH, we require 26 grams of NaOH.
Explanation of Solution
Given density of CH3OH as 0.79 g/cm3
Volume of CH3OH 100 mL
Given the mass percent of NaOH is 25% which indicates that 100 g of solution contains 25 g of NaOH solute.
Mass of NaOH solute = 25 g
Mass of solution = 100 g
Hence, Mass of solution = Mass of NaOH solute + Mass of solvent
OR
Mass of solvent = Mass of solution − Mass of NaOH solute
= 100 g - 25g
= 75 g
In other words to prepare 25% NaOH solution by mass, 25g of NaOH solute is dissolved in 75 g of solvent.
In order to find out the mass of NaOH required to prepare 25% solution in 100 ml solvent, the mass of CH3OH is multiplied by mass percentage conversion factor:
Therefore, to prepare 100 mL of 15% NaOH solution, we need to dissolve 18g of NaOH in 100mL of water.
Therefore, to prepare 100 mL of 25% NaOH solution, we need to dissolve 26g of CH3OH in 100mL of water.
(d)
Interpretation:
The mass of
Concept Introduction:
The measure of concentration of solute in solution or the amount of substance that is present in a specified amount of mass of solvent is termed as Molality.
Molarity is the number of moles of solute per liter of solution. Most of the solution concentration is indicated in terms of Molarity as it will indicate the volume of solvent or amount of solute.
Mole fraction is the number of molecules of particular component in a mixture divided by total number of moles
(d)

Answer to Problem 22E
To prepare 100 ml of 0.10 mole of
Explanation of Solution
Given density of water as 1.00 g/cm3
Volume of water 100 ml
To compute the number of moles of water required
To find the mole fraction of
Hence, mole fraction of
To get the number of moles of water,
Mole fraction of
Also, we found that no. of moles of water present in 100 ml is 5.55 mol
Molar mass of
To compute the mass of
Therefore, to prepare 100 ml of 0.10 mole of
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Chapter 17 Solutions
Chemical Principles
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