Chapter 10, Problem 193A

Interpretation Introduction

(a)

Interpretation:

Number of moles in 1 g of L-tryptophan must be found.

Concept introduction:

The number of moles is related to mass and molar mass as follows:

Number of moles $\text{=}\frac{\text{mass}}{\text{molar mass}}\text{.}$

Answer to Problem 193A

Number of mole of L-tryptophan is 0.005 mol

Explanation of Solution

The molar mass of C, H, N and O is 12 g/mol, 1 g/mol, 14 g/mol and 16 g/mol respectively.

Molar mass of L-tryptophan (C₁₁H₁₂N₂O₂)

$\begin{array}{l}\text{=(11×12+12×1+2×14+2×16) g/mol}\\ \text{=(132+12+28+32) g = 204 g/mol}\end{array}$

Mass is given 1 g thus, number of moles can be calculated as follows:

Number of mol $=\frac{1\text{ g}}{204\text{ g/mol}}=0.0049\approx 0.005\text{ mol}$

b)

Interpretation Introduction

Interpretation:

Number of moles in 1 g of magnesium sulfate heptahydrate must be found.

Concept introduction:

The number of moles is related to mass and molar mass as follows:

Number of moles $\text{=}\frac{\text{mass}}{\text{molar mass}}\text{.}$

Answer to Problem 193A

Number of mole of magnesium sulfate heptahydrate is 0.004 mol.

Explanation of Solution

Molecular formula of magnesium sulfate heptahydrate is MgSO₄.7H₂O. Here, molar mass of Mg, S, O and H is 24 g/mol, 32 g/mol, 16 g/mol and 1 g/mol respectively.

Thus, molar mass of H₂O is 18 g/mol.

Molar mass of magnesium sulfate heptahydrate (MgSO₄.7H₂O)

$\begin{array}{l}\text{=(1×24+1×32+4×16+7×18) g/mol}\\ \text{=(24+32+64+126) g = 246 g/mol}\end{array}$

Now, number of moles can be calculated as follows:

Number of mol $=\frac{1\text{ g}}{246\text{ g/mol}}=0.004\text{ mol}$

c)

Interpretation Introduction

Interpretation:

Number of moles in 1 g of propane needs to be determined.

Concept introduction:

The number of moles is related to mass and molar mass as follows:

Number of moles $\text{=}\frac{\text{mass}}{\text{molar mass}}\text{.}$

Answer to Problem 193A

Number of mole of propane is 0.023 mol.

Explanation of Solution

The molar mass of C and H is 12 g/mol and 1 g/mol respectively.

Molar mass of propane (C₃H₈)

$\text{=(3×12+8×1) g/mol = (36+8) g/mol = 44 g/mol}$

The number of moles can be calculated as follows:

Number of mol $=\frac{1\text{ g}}{44\text{ g/mol}}=0.0227\text{ mol}\approx 0.023\text{ mol}$