CHEM 1411 Chapter 3 Practice Test Newton 5

Laredo Community College Science Department

CHEM 1411

Practice Test Chapter 3 Newton 1

Part I. Multiple Choice

Circle the letter of the BEST answer on the test here. When you have finished, use a #2 pencil (provided) and completely darken the letter on the Scantron form which corresponds to your choice. If you make a mistake, erase the wrong answer completely. Each question is worth 3 points.

1. In a balanced equation, what is balanced? (A) atoms (B) moles (C) molecules (D) atoms and molecules (E) moles and atoms

2. The value of Avogadro’s number is mol-1 . (A) 2.179 x 10-19 (B) 2.998 x 108 (C) 6.626 x 10-34 (D) 6.022 x 1023 (E) 9.109 x 10-28

3. The formula for methanol is CH3OH. This means that, in methanol, .

Atomic Masses

H 1.0 g mol-1 C 12.0 g mol-1 N 14.0 g mol-1 O 16.0 g mol-1

(A) for every 100 atoms of carbon there are 300 atoms of hydrogen and 100 hydroxide ions. (B) for every gram of hydrogen there are twelve grams of carbon. (C) for every twelve grams of carbon there are sixteen grams of oxygen. (D) the compound is 33% oxygen by mass. (E) the compound is 50% hydrogen by mass.

4. The molar mass (to the nearest whole number) of anhydrous iron(II) sulfate, FeSO4 , is grams per mole. (A) 104 (B) 152 (C) 248 (D) 336 (E) 400

5. A sample of Fe2O3 was found to contain 10.2 g of iron. How many moles of iron are there in the sample? (A) 0.180 (B) 0.360 (C) 2.00 (D) 3.60 CHEM 1411 Chapter 3 Practice Test Newton 2

6. The expression “one mole of copper(II) sulfide” refers to the mass of . (A) copper(II) sulfide needed to occupy one liter of solution (B) solid copper(II) sulfide needed to occupy 22.4 L at STP. (C) copper combined with sulfur in one molecule. (D) copper(II) sulfide in grams equal to one formula molar mass (E) one molecule (in grams) of copper(II) sulfide

7. Why is this equation incorrect? Mg3 + N2  Mg3N2 (A) Some of the subscripts are incorrectly used. (B) The equation is not balanced. (C) The valence of the nitride ion is incorrect. (D) The valence of the magnesium ion is incorrect. (E) The coefficient of N2 is incorrect.

8. Which procedure can be used to demonstrate experimentally that the reaction below obeys the Law of Conservation of Matter? 2 Mg + O2  2 MgO

(A) Take a mass of 1.0000 g of Mg ribbon, burn it in pure O2, and compare the mass of the product with the original mass of the Mg. (B) Show that the sum of 2 atomic molar masses of Mg plus 1 molar mass of O2 is equal to 2 molar masses of MgO. (C) Determine the mass of a sealed flash-bulb containing magnesium and oxygen, ignite the mixture, cool, and compare the final mass of bulb plus contents with the original mass of the bulb plus contents. (D) Burn 1.0000 g of Mg ribbon in a tall beaker filled with air, scrape out all of the MgO formed, and compare with the original mass of the Mg.

9. The chemical equation 2 CO2  2 CO + O2 informs us that . (A) when 2 mol of CO2 decompose, less than 2 mol of CO will be formed and the quantity of O2 formed will be less than 1 mol (B) only under special conditions will 2 mol of CO2 yield 2 mol of CO and l mol of O2 (C) carbon dioxide decomposes, but that the relative amounts of CO2, CO, and O2 involved in the reaction are a function of conditions. (D) regardless of conditions, the decomposition of l mol of CO2 will yield l mol of CO and 1/2 mole of O2 (E) the tendency of CO2 to decompose is equal to the tendency of CO and O2 to combine

10. What is the percentage of oxygen by mass in (NH4)3PO4? (A)  100 % (B)  100 % (C)  100 % (D)  100 %

11. A compound of which halogen is used in etching glass? (A) astatine (B) iodine (C) bromine

CHEM 1411 Chapter 3 Practice Test Newton 3

(D) chlorine (E) fluorine

12. Which of the following compounds will produce a product other than carbon dioxide and water upon combustion in an atmosphere of pure oxygen? (A) CH4 (B) C2H6 (C) C6H5NH2 (D) CH3OCH2CH3 (E) C32H44O9

13. Substances that contain water incorporated in the crystal in definite proportions by weight are . (A) anhydrous. (B) amorphous. (C) hydrates. (D) polymorphous. (E) zeolites.

14. The empirical formula of a sugar is CH2O. If the sugar has a molecular weight of 148 ± 4 amu, the molecular formula of the compound is . (A) CH2O (B) CH2O5 (C) C5H5O5 (D) C5H10O5 (E) C5H10O

15. How many moles of Fe are needed to produce 16.0 mol of H2, according to the equation below?

4 H2O(g) + 3 Fe(s)  Fe3O4(s) + 4 H2(g)

(A) 3.00 mol (B) 12.0 mol (C) 16.0 mol (D) 21.3 mol

16. The element molybdenum has been prepared by the reduction of molybdenum trioxide by hydrogen according to the balanced equation below.

MoO3(s) + 3 H2(g)  Mo(s) + 3 H2O(g)

When 24.0 g of molybdenum trioxide reacts with 1.0 g of hydrogen measured at STP, the mass of molybdenum produced was 14.4 g. What is the percent yield of molybdenum?

Molar Masses (g mol–1)

Mo 95.94 MoO3 143.94 H2 2.0

(A) 100.% (B) 90.0% (C) 60.7% (D) 50.6%

17. A hydrocarbon (CxHy) was burned completely in air yielding 0.18 g of water and 0.44 g of carbon dioxide. Which formula could give such data?

CHEM 1411 Chapter 3 Practice Test Newton 4

Molar Masses (g mol–1)

CO2 44.0 H2O 18.0

(A) C2H2 (B) C2H4 (C) C2H6 (D) C6H6

Part II. Short Answer

Answer each question in the space provided on. The point value of each question is shown with the question. Use the back of the page if you need more room.

1. Balance the following chemical equations using small whole number coefficients. Be sure to include a coefficient in each blank. (6)

a) C6H12O6 + O2  CO2 + H2O

b) H3PO4 + Ca(OH)2  Ca3(PO4)2 + H2O

c) (NH4)2Cr2O7  Cr2O3 + N2 + H2O

Show all work, including units, for the word problem. Record your answers to the proper number of significant figures.

Partial credit may be earned, but all work (with appropriate units) must be shown in order to receive full credit for the problem. No credit will be given for an answer only. Circle your final answers.

2. Laboratory tests have confirmed the presence of the nerve agent Sarin inside a roadside bomb which exploded in Baghdad. The elemental composition of Sarin is given in the table below. The molecular weight of the compound is 140 amu.

34.29 % C C 12.01 amu 7.19 % H H 1.008 amu 22.84 % O O 16.00 amu 13.56 % F F 19.00 amu 22.11 % P P 30.97 amu

a) What is the empirical formula of Sarin? (4)

b) What is the molecular formula of Sarin? (2)