Chapter 7, Problem 7.AE

(a)

Interpretation Introduction

Interpretation:

The formula mass of ascorbic acid has to be calculated.

Concept introduction:

Formula mass is defined as addition of atomic mass of atoms of the compound in empirical formula.  The unit is atomic mass unit(amu)

Answer to Problem 7.AE

The formula mass of ascorbic acid is $176.124\text{g/mol}$.

Explanation of Solution

To calculate: The formula mass of ascorbic acid.

The molecular formula of ascorbic acid is ${\text{C}}_{\text{6}}{\text{H}}_{\text{8}}{\text{O}}_{\text{6}}$

The formula mass is determined as follows,

$\begin{array}{l}=\text{6(atomic mass of C) + 8(atomic mass of H)}\text{+ 6(atomic mass of 0) }\\ \\ \text{= 6( 12}\text{.010 6) + 8(1}\text{.007 98) + 6(15}\text{.999 4)}\\ \\ =176.124\text{g/mol}\end{array}$

(b)

Interpretation Introduction

Interpretation:

The molarity of ${\text{I}}_{\text{3}}{}^{\text{-}}$ solution has to be calculated.

Concept introduction:

Molarity can be defined as the moles of solute (in grams) to the volume of the solution (in litres). The molarity of a solution can be given by the formula,

$\text{Molarity(M)=}\frac{\text{Moles}\text{of}\text{solute(in}\text{mol)}}{\text{Volume}\text{of}\text{solution(in}\text{L)}}$

Answer to Problem 7.AE

The molarity of ${\text{I}}_{\text{3}}{}^{\text{-}}$ solution is $\text{0}\text{.038 03 M}$.

Explanation of Solution

To calculate: The molarity of ${\text{I}}_{\text{3}}{}^{\text{-}}$ solution.

The molecular weight of ascorbic acid is $176.124\text{g/mol}$.

The number of moles of ascorbic acid is calculated as

$\begin{array}{l}\text{Mole}\text{=}\frac{\text{Given}\text{weight}}{\text{Molecular}\text{weight}}\\ \\ =\frac{\text{0}\text{.1970 g}}{\text{176}\text{.124 g/mol}}=\text{1}\text{.118 5 mmol}\end{array}$

There are equal number of moles for both ascorbic acid and ${\text{I}}_{\text{3}}{}^{\text{-}}$.  Thus, the molarity is calculated as

$\begin{array}{l}\text{Molarity of}{\text{I}}_{\text{3}}{}^{\text{-}}\text{ = 1}\text{.118 5 mmol/29}\text{.41 mL}\\ \\ \text{= 0}\text{.03803 M}\end{array}$

(c)

Interpretation Introduction

Interpretation:

The mass percentage of ascorbic acid in given tablet has to be calculated.

Concept introduction:

The mass percentage of compound can be calculated by taking the calculated mass of the substance to the total mass of the sample whole multiplied by 100.

The mass percent can be calculated with formula,

$\text{Mass}\text{percent(in}\text{percentage)=}\frac{\text{Calculated}\text{mass(in}\text{grams)}}{\text{total}\text{mass(in}\text{grams)}}\text{×100}$

$\text{Molar}\text{mass}\text{=}\frac{\text{Mass}}{\text{Mole}}$

Molarity can be defined as the moles of solute (in grams) to the volume of the solution (in litres). The molarity of a solution can be given by the formula,

$\text{Molarity(M)=}\frac{\text{Moles}\text{of}\text{solute(in}\text{mol)}}{\text{Volume}\text{of}\text{solution(in}\text{L)}}$

Answer to Problem 7.AE

The mass percentage of ascorbic acid in given tablet is $\text{49}\text{.94}\text{\%}$.

Explanation of Solution

To calculate: The mass percentage of ascorbic acid in given tablet.

The number of moles of  ${\text{I}}_{\text{3}}{}^{\text{-}}$ is calculated as

$\begin{array}{l}\text{=}\text{0}\text{.03803}\text{(mol/L)}\text{×}\text{0}\text{.03163}\text{L}\\ \\ \text{=}\text{0}\text{.001203}\text{mol}\end{array}$

There are equal number of moles for both ascorbic acid and ${\text{I}}_{\text{3}}{}^{\text{-}}$.

$\text{Moles}\text{=}\text{0}\text{.001203}\text{mol}\text{of}\text{ascorbic}\text{acid}$

The mass of ascorbic acid is derived from molecular weight of ascorbic acid

$\begin{array}{l}\text{=}\text{176}\text{.124g/mol}\text{×}\text{0}\text{.001203}\text{mol}\\ \\ \text{=}\text{0}\text{.2119}\text{g}\end{array}$

The mass percent of ascorbic acid in given tablet is

$\text{Mass}\text{percent}\text{=}\frac{\text{0}\text{.2119}\text{g}}{\text{0}\text{.4242}\text{g}}\text{×100}\text{=}\text{49}\text{.94}\text{\%}\text{of}\text{ascorbic}\text{acid}\text{in}\text{tablet}$