Chapter 14, Problem 2STP

Interpretation Introduction

Interpretation:

Amount of bromine (Br₂) in 55 gm of solution 4 has to be calculated.

Concept introduction:

Composition of a solution can be defined by expressing its concentration. Concentration can be expressed either qualitatively or quantitatively. There are several ways by which we can describe the concentration of the solution quantitatively. Some commonly used quantitative descriptions are percent by mass, percent by volume, molarity, molality and mole fraction.

Mass percentage or percent by mass (w/W): The mass percentage of a component of a solution is defined as:

$\mathrm{Mass}\%ofacomponent=\frac{Mass of the component in the solution}{Total mass of the solution}\times 100$

Volume/volume percentage (v/V percent): Percent by volume is expressed as the ratio of the volume of the solute to the total volume of the solution multiplied by 100.

In expression,

$\mathrm{Volume}percentage\left(v/V\right)\%ofacomponent=\frac{Volumeof the solute}{Total volume of the solution}\times 100$

Answer to Problem 2STP

Answer is D. 0.2628 gm of bromine (Br₂) is present in 55 gm of solution 4.

Mass percentage or percent by mass (w/W): The mass percentage of a component of a solution is defined as:

$\mathrm{Mass}\%ofacomponent=\frac{Mass of the component in the solution}{Total mass of the solution}\times 100$

Data given: Total mass of the solution = 55 gm

Percent by mass = 0.4779

$\begin{array}{l}Masspercentage=\frac{Massof bromineinthesolution}{Total mass of the solution}\times 100\\ Massof bromineinthesolution=\frac{Masspercentage\times Total mass of the solution}{100}\\ \mathrm{Mass}of bromineinthesolution=\frac{0.4779\times 55gm}{100}=0.2628gm\end{array}$

Answer is D.

Reasons for incorrect options:

As it can be seen that mass of bromine calculated from the equation:

$\begin{array}{l}Masspercentage=\frac{Massof bromineinthesolution}{Total mass of the solution}\times 100\\ Massof bromineinthesolution=\frac{Masspercentage\times Total mass of the solution}{100}\\ \mathrm{Mass}of bromineinthesolution=\frac{0.4779\times 55gm}{100}=0.2628gm\end{array}$

So, 0.2628 gm of bromine (Br₂) is present in 55 gm of solution 4.

That means other options that is,

a. 3.560 g

b. 0.084 98 g

c. 1.151 g

are not found by this equation, that makes them incorrect.

Explanation of Solution

Mass percentage or percent by mass (w/W): The mass percentage of a component of a solution is defined as:

$\mathrm{Mass}\%ofacomponent=\frac{Mass of the component in the solution}{Total mass of the solution}\times 100$

Data given: Total mass of the solution = 55 gm

Percent by mass = 0.4779

$\begin{array}{l}Masspercentage=\frac{Massof bromineinthesolution}{Total mass of the solution}\times 100\\ Massof bromineinthesolution=\frac{Masspercentage\times Total mass of the solution}{100}\\ \mathrm{Mass}of bromineinthesolution=\frac{0.4779\times 55gm}{100}=0.2628gm\end{array}$

Answer is D.

Conclusion

Reasons for incorrect options:

As it can be seen that mass of bromine calculated from the equation:

$\begin{array}{l}Masspercentage=\frac{Massof bromineinthesolution}{Total mass of the solution}\times 100\\ Massof bromineinthesolution=\frac{Masspercentage\times Total mass of the solution}{100}\\ \mathrm{Mass}of bromineinthesolution=\frac{0.4779\times 55gm}{100}=0.2628gm\end{array}$

So, 0.2628 gm of bromine (Br₂) is present in 55 gm of solution 4.

That means other options that is,

a. 3.560 g

b. 0.084 98 g

c. 1.151 g

are not found by this equation, that makes them incorrect.