Log out Go to App
Go to App

Learning Materials

Features

Discover

Chapter 13: Problem 75

Thiophene \(\left(\mathrm{fp}=-38.3 ; \mathrm{bp}=84.4^{\circ} \mathrm{C}\right)\) is a sulfur containing hydrocarbon sometimes used as a solvent in place of benzene. Combustion of a \(2.348 \mathrm{g}\) sample of thiophene produces \(4.913 \mathrm{g} \mathrm{CO}_{2}, 1.005 \mathrm{g} \mathrm{H}_{2} \mathrm{O},\) and \(1.788 \mathrm{g} \mathrm{SO}_{2} .\) When a \(0.867 \mathrm{g}\) sample of thiophene is dissolved in \(44.56 \mathrm{g}\) of benzene \(\left(\mathrm{C}_{6} \mathrm{H}_{6}\right),\) the freezing point is lowered by \(1.183^{\circ} \mathrm{C} .\) What is the molecular formula of thiophene?

Short Answer

Expert verified
The molecular formula of thiophene is \( C_{4}H_{4}S \).

Step by step solution

01

Determine empirical formula from combustion products

Write the combustion reaction: \(C_{n}H_{m}S + aO_{2} \rightarrow bCO_{2} + cH_{2}O + dSO_{2}\). We know that combustion produces water, carbon dioxide, and sulfur dioxide. From stoichiometric coefficients, we can find that \(n=b\), \(m=2c\), and \(1=d\). Now, find the amount (mol) of each product by dividing weight by the molecular weight. You obtain: \(b = 4.913g/44.01g/mol = 0.1116 mol\), \(c = 1.005g/18.02g/mol = 0.0557 mol\), and \(d = 1.788g/64.07g/mol = 0.0279 mol\). Now, calculate \(n, m\), and the empirical formula.
02

Find molar mass from freezing point depression and find molecular formula

According to the formula \(\Delta T = K_f * m\), where \(\Delta T = 1.183^{\circ} C\) is the freezing point depression, \(K_f = 5.12 C*mol/g\) is the molal freezing point depression constant for benzene, and \(m=n_2m_2/n_1\) is the molality of the solution, solve for \(m\), where \(n_2 = mass_2/M_2\), and \(M_2\) is what you're looking for. Given that \(mass_2 = 0.867g\), and \(n_1 = 44.56g/78.12g/mol = 0.570 mol\), \(M_2 = mass_2/(m*n_1)\). Then find the molecular formula knowing that the ratio of molar mass to the mass corresponding to empirical formula equals to the ratio of numbers of atoms.
03

Calculate empirical formula mass

Given the empirical formula obtained in step 1, calculate the empirical formula mass by adding up the atomic masses of the elements. For \( C_{4}H_{4}S \), the empirical formula mass is \(4*12.00g/mol + 4*1.01g/mol + 32.07g/mol = 68.15g/mol\).
04

Calculate molar mass and molecular formula

Using the formula obtained in step 2, calculate \(M_2\) . Then, find the ratio of the \(M_2\) to empirical formula mass, which should be an integer. If it's not equal to one, multiply the empirical formula by this number to get the molecular formula.

Unlock Step-by-Step Solutions & Ace Your Exams!

  • Full Textbook Solutions

    Get detailed explanations and key concepts

  • Unlimited Al creation

    Al flashcards, explanations, exams and more...

  • Ads-free access

    To over 500 millions flashcards

  • Money-back guarantee

    We refund you if you fail your exam.

Start your free trial

Over 30 million students worldwide already upgrade their learning with Vaia!

One App. One Place for Learning.

All the tools & learning materials you need for study success - in one app.

Get started for free

Most popular questions from this chapter

NaCl(aq) isotonic with blood is \(0.92 \%\) NaCl (mass/volume). For this solution, what is (a) \(\left[\mathrm{Na}^{+}\right]\) (b) the total molarity of ions; (c) the osmotic pressure at \(37^{\circ} \mathrm{C} ;\) (d) the approximate freezing point? (Assume that the solution has a density of 1.005 g/mL.)

Calculate the mole fraction of the solute in the following aqueous solutions:(a) \(0.112 \mathrm{M} \mathrm{C}_{6} \mathrm{H}_{12} \mathrm{O}_{6}\) \((d=1.006 \mathrm{g} / \mathrm{mL})\) (b) \(3.20 \%\) ethanol,by volume \((d=0.993 \mathrm{g} / \mathrm{mL}\) pure \(\left.\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{OH}, d=0.789 \mathrm{g} / \mathrm{mL}\right)\).

A 0.72 g sample of polyvinyl chloride (PVC) is dissolved in \(250.0 \mathrm{mL}\) of a suitable solvent at \(25^{\circ} \mathrm{C}\). The solution has an osmotic pressure of \(1.67 \mathrm{mm} \mathrm{Hg}\). What is the molar mass of the PVC?

Calculate the vapor pressure at \(20^{\circ} \mathrm{C}\) of a saturated solution of the nonvolatile solute, urea, \(\mathrm{CO}\left(\mathrm{NH}_{2}\right)_{2},\) in methanol, \(\mathrm{CH}_{3} \mathrm{OH} .\) The solubility is \(17 \mathrm{g}\) urea/100 \(\mathrm{mL}\) methanol. The density of methanol is \(0.792 \mathrm{g} / \mathrm{mL}\), and its vapor pressure at \(20^{\circ} \mathrm{C}\) is \(95.7 \mathrm{mmHg}\).

At 1.00 atm, the solubility of \(\mathrm{O}_{2}\) in water is \(2.18 \times 10^{-3} \mathrm{M}\) at \(0^{\circ} \mathrm{C}\) and \(1.26 \times 10^{-3} \mathrm{M}\) at \(25^{\circ} \mathrm{C}\) What volume of \(\mathrm{O}_{2}(\mathrm{g}),\) measured at \(25^{\circ} \mathrm{C}\) and \(1.00 \mathrm{atm},\) is expelled when \(515 \mathrm{mL}\) of water saturated with \(\mathrm{O}_{2}\) is heated from 0 to \(25^{\circ} \mathrm{C}\) ?
See all solutions

Recommended explanations on Chemistry Textbooks

Ionic and Molecular Compounds

Read Explanation

The Earths Atmosphere

Read Explanation

Kinetics

Read Explanation

Inorganic Chemistry

Read Explanation

Chemical Reactions

Read Explanation

Nuclear Chemistry

Read Explanation
View all explanations

What do you think about this solution?

We value your feedback to improve our textbook solutions.

Study anywhere. Anytime. Across all devices.

Sign-up for free