Chapter 7, Problem 7.79UTC

Interpretation Introduction

To determine:

Molecular formula, molar mass and number of moles in 10 g of given compounds.

Answer to Problem 7.79UTC

Compound 1:

Molecular formula  Molar mass  Number of moles in 10 g

$S_{2}C{l}_2$   135.06 g/ mol  0.074054 mol

Compound 2:

Molecular formula  Molar mass  Number of moles in 10 g

$C_6{H}_6$   78.066 g/ mol  0.1281 mol

Explanation of Solution

Given:

a. Formula of a chemical species is given by ${\text{A}}_{\text{o}}{\text{B}}_{\text{l }}$,

where A, B are the symbols of the elements, o and l are the number of A and B elements in the molecule.

Here, in first compound, o = 2, l = 2 and in second compound o = 6, l = 6. So, formulas are $S_{2}C{l}_2$ and $C_6{H}_6$.

Formula used:

b. Molar mass of a compound,

${\text{A}}_{\text{o}}{\text{B}}_{\text{l }}\text{= o×Atomic Mass of A + l× Atomic Mass of B }$ - (1)

c. The number of moles, n

$\text{n}\text{=}\frac{\left(\text{Mass of substance}\text{in grams}\right)}{\text{(Molar}\text{Mass in g/mol)}}$ - (2)

Calculation:

b. Using equation (1), Molar mass of $S_{2}C{l}_2$ = $\text{2× 32}\text{.065 + 2×35}\text{.453 = 135}\text{.036 g/ mol}$

Molar mass of $C_6{H}_6$ = $\text{6×12}\text{.011 + 1×6 = 78}\text{.066 g/ mol}$

Using equation (2),

Number of moles of $S_{2}C{l}_2$ in 10 g = $\frac{\text{10}\text{g}}{\text{135}\text{.036}\text{g/mol}}\text{=}\text{0}\text{.074054}\text{mol}$

Number of moles of $C_6{H}_6$ in 10 g = $\frac{\text{10}\text{g}}{78.066\text{g/mol}}\text{=}\text{0}\text{.1281}\text{mol}$

Conclusion

Molecular formula of compound,1 = $S_{2}C{l}_2$, molar mass=135.036 g/ mol and number of moles in 10 g of substance is 0.074054 mol.

Molecular formula of compound, 2 = $C_6{H}_6$, molar mass= 78.066 g/ mol and number of moles in 10 g of substance = 0.1281 mol.