Sample Solution from
Quantitative Chemical Analysis
9th Edition
ISBN: 9781464135385
Chapter 1
Problem 1.AE
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(a)

Interpretation Introduction

Interpretation:

Molarity of 500 mL methanol solution of 25.00 mL methanol in chloroform has to be calculated.

Concept Introduction:

Molarity is one of the parameters used to express concentration of a solution.  It is expressed as,

Molarity = number of moles of solutevolume of solution in L

Expert Solution

Answer

Answer:

Molarity of 500 mL methanol solution made of 25.00 mL methanol in chloroform is calculated as 1.235 M.

Explanation of Solution

Explanation:

Calculate the number of moles of solute methanol to determine.

Given that volume of methanol is 25.00 mL this can be converted to mass as,

density = massvolume

Rewriting the above equation to calculate mass of methanol,

mass=volume×density

Given that density of methanol is 0.7914 g/mL. Therefore,

mass of methanol = 25.00 mL ×0.7914 g/mL = 19.785 g

no.of moles of methanol = massmolar mass = 19.785 g32.04 g/mol =   0.6175 mol

Volume of solution is 500 mL(= 0.5 L)

Now calculate the molarity of methanol in 500 mL solution containing 25.00 mL (=25.00 g) of methanol as shown below,

Molarity  = number of moles of methanolvolume of solution in L = 0.6175 mol0.5 L = 1.235 M

Conclusion

Conclusion: 

Given the density of methanol solution, its molarity is calculated using relevant formula.

(b)

Interpretation Introduction

Interpretation:

Molality of 500 mL methanol solution of 25.00 mL methanol in chloroform has to be calculated.

Concept Introduction:

Molality is one of the many parameters that is used to express concentration of a solution.  It is expressed as,

Molality = number of moles of solutemass of solvent in kg

Expert Solution

Answer

Answer:

Molality of 500 mL methanol solution made of 25.00 mL methanol in chloroform is calculated as 0.873 m.

Explanation of Solution

Explanation:

Volume of solution is 500 mL.  It is converted to mass –

density = massvolume

Rewriting the above equation to calculate mass of solution,

mass=volume×density

Given that density of solution is 1.454 g/mL. Therefore,

mass of solution = 500 mL ×1.454 g/mL = 727 g

727 g of solution contains 25.00 mL of methanol which is equivalent to 19.785 g methanol as calculated in previous step.  Therefore mass of solvent chloroform is,

727 g of solution  = 19.78 g of methanol + mass of chloroformmass of chloroform      = 727 g - 19.785 g  = 707.215 g = 0.707215 kg

Number of moles of methanol as calculated in previous step is 0.6175 mol.

Molality of methanol is calculated as,

Molality of methanol = number of moles of methanolmass of chloroform in kg = 0.6175 mol0.707215 = 0.873 m

Conclusion

Conclusion: 

Given the density of methanol solution, its molality is calculated using relevant formula.

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