Review Sheet-Chapter 3



Intro Material #2 Review Sheet

1. Chromium, Cr, has 4 isotopes. What is the average atomic weight of chromium? Does your answer make sense?

Mass Number Isotopic mass (amu) Fractional Abundance

50 49.9461 0.0435

52 51.9405 0.8379

53 52.9407 0.0950

54 53.9389 0.0236

2. Naturally occurring boron, atomic number 5, is a mixture of two isotopes, boron-10 and boron-11. The isotopes have masses of 10.0129 and 11.00931 amu, respectively. Without using a calculator, choose the best estimate among the following for the percent abundance of the two boron isotopes:

i) 40% 10B and 60% 11B

ii) 80% 10B and 20% 11B

iii) 20% 10B and 80% 11B

iv) 60% 10B and 40% 11B

3. Write an equation or put the equation into words for each of the following:

a) 2 molecules of solid potassium, K, react with 1 molecule of chlorine gas, Cl2, to yield 2 molecules of solid potassium chloride, KCl.

b) 2 Mg (s) + O2 (g) → 2 MgO (s)

4. When hydrocarbon fuels undergo complete combustion, carbon dioxide and water are produced. Extensive use of fossil fuels, composed of hydrocarbons, poses an environmental concern because carbon dioxide is a major contributor to the “greenhouse effect”. Consider the burning of gasoline in an automobile engine. Assume that gasoline is composed entirely of the hydrocarbon octane, C8H18, and that the only emission products are carbon dioxide and water. (In actuality, the combustion in an automobile engine is incomplete and CO is also produced.) Write a balanced equation for the combustion of octane.

5. Calculate the molar mass of cobalt(III)chloride, methanol (CH3OH) and ethyl ether (CH3CH2OCH2CH3).

6. Phenol, a general disinfectant, is 76.57% C, 6.43% H and 17.00% O, by mass. What is the empirical formula of phenol?

7. Consider the reaction: Fe2O3 (s) + 3 CO (g) → 2 Fe (s) + 3 CO2 (g)

A. What is the maximum amount, moles, of carbon dioxide that can be produced from the reaction of 10.5 moles of iron (III) oxide, Fe2O3 with 10.5 moles CO?

B. What mass, in grams, of carbon dioxide can be produced from 10.5 grams of iron (III) oxide, Fe2O3?

C. What mass of Fe2O3 is needed to produce 3.00 g Fe?

D. How much carbon dioxide is actually produced if the percent yield of part B was 72%?

8. How many molecules are in 4.0 moles of hydrogen gas, H2?

9. How many molecules are in 4.0 grams of hydrogen gas, H2?

10. How many H atoms are in 4.0 grams of hydrogen gas, H2?

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