CHEM 1215 Help Session

Saturday, April 29, 200

First Question

Exam II, Problem #8, Spring, 2000 CHEM 1215:

Two isotopes of copper exist in nature. 30.80% of copper is 65Cu with a mass of 64.9278 u. What is the mass of the other isotope of copper?

Setup

Solution

Second Question

Exam II, Problem #6, Spring, 2000 CHEM 1215:

A 60.0 gram sample of aluminum metal, initially at 23.5 ÐC is carefully added to 100. gram sample of water at 55.0 ÐC. Calculate the final temperature of the mixture. Note: the specifi heat of aluminum is 0.900 J­g-1­ÐC-1.

Setup

Substituting

Solving

Final Comments

Third Question

Exam I, Problem #9, Spring, 2000 CHEM 1215:

An aqueous solution of concentrated ammonia, NH3, is 58.0% pure ammonia (by weight). A 255 mL sample of concentrated ammonia solution was found to contain 133 grams of pure ammonia. Calculate the density of the concentrated ammonia solution.

Setup

Substituting and Solving

Fourth Question

Exam I, Problem #5c, Spring, 2000 CHEM 1215:

a fertilizer suggests an application of 2.06 x 10-1 kg­m-2. Convert to pounds­foot-2.

Setup and solution

Final Comments

Fifth Question

Final Exam, Problem #2, Fall, 1998 CHEM 1215:

Peanut oil has a density of 0.920 g­mL-1. A recipe calls for 0.667 cups of peanut oil (1 cup = 0.225 L). Calculate the mass, in grams, of peanut oil in this particular recipe.

Setup and solution

Sixth Question

Exam III, Problem #7a and b, Spring, 2000 CHEM 1215:

7a) In laboratory last week everyone reacted copper with nitric acid, according to the equation

3Cu(s) + 8HNO3(aq) -> 2NO(g) + 3Cu(NO3)2(aq) + 4H2O(l)

Calculate the number of moles and the number of grams of NO formed when 1.17 grams of copper metal reacted with excess nitric acid.

Setup and solution

b) NO is a colorless gas which reacts immediately with O2 in the atmosphere according to the equation

2NO(g) + O2(g)  -> 2NO2(g)

Calculate the number of grams of NO2 formed when the 1.17 gram sample of copper in part a) reacts.

Setup and solution