Chemistry Answers

62. Methylbenzene (toluene), CHI;CH;(1), is a common

paint thinner. It can be prepared from benzene, Cattal

CH,CI(g) + CoHo(1) > CH;CH;() + HCK(g)

In an investigation, 25.0 g of benzene is combined

with 20.0 g of chloromethane, CH, C1, in the presence

of an appropriate catalyst. (7.4, 7.5)

(a) Calculate the theoretical yield of toluene.

(b) If 22.0 g of CH, CH, is actually obtained, what is the

percentage yield?

(c)

Suggest reasons for the discrepancy between the

actual yield and the theoretical yield.

Suppose that 181.1 J of heat energy is required to completely vaporize 3.9 g of a pure liquid. If the molar mass of the liquid is 128.34 g/mol, what is the molar enthalpy of vaporization of the liquid?

4. What is the purpose of adjusting the polarity?

5. Would benzoic acid dissolve better in water, or in ethanol? Explain why using the concepts discussed in this laboratory.

In a final very careful and correct recrystallization from acetone, benzoic acid (pure mp 122-122.3°C) was melted on a melting point machine immediately after vacuum filtration and washing, and found to have a melting point of 116-121°C. Why is the melting point not

122-122.3°C? Assume that there are no solid compounds present other than benzoic acid present, and suggest what may be present to affect melting point, and what role that presence does.

2. What are 2 advantages of using gravity filtration over vacuum filtration when removing a solid impurity from a hot mixture?

3. If iron filings were an impurity present along with the ASA in this experiment, at which point in the recrystallization procedure would they be removed completely from the ASA? (What slide numbers show this procedure?)

An actual yield of 18g, the theoretical yield is unknown. Calculate the theoretical yield?

During a combustion reaction of H and O, H2O was produced. What is the limiting reactant in the reaction? And why?

72cm³ of a mixture of Nitrogen and Nitrogen oxide were passed over heated copper until all the nitrogen oxide had been reduced to nitrogen. The volume of the resulting gas was 60cm³, calculate the volume of nitrogen oxide in the original mixture.

130cm³ of air were passed through heated carbon. The resulting gas consisted a Carbon monoxide and nitrogen and the volume of Carbon monoxide was 54cm³. Calculate the volume of Nitrogen.

Why do scientists sometimes discard theories?