CHE 11, Fall 1998
Test 1
September 28, 1998

Multiple choice, 2 points each
1. The statement "The total mass of materials is not affected by a chemical change in those materials" is called a(n)

(a) observation.

(b) measurement.

(c) theory.

(d) natural law.

(e) experiment.

2. According to the law of definite proportion,

(a) if the same two elements form two different compounds, they do so in the same ratio.
(b) it is not possible for the same two elements to form more than one compound.
(c) the ratio of the masses of the elements in a compound is always the same.
(d) the total mass after a chemical change is the same as before the change.

3. Which of the following statements about ions is false?

(a) Ions are formed by adding electrons to a neutral atom.
(b) Ions are formed by changing the number of protons in an atom’s nucleus.
(c) Ions are formed by removing electrons from a neutral atom.
(d) An ion has a positive or negative charge.
(e) Metals tend to form positive ions.

4. Given the equation 3A + B C + D. If you carry out the reaction by combining 2 moles of A with 1 mole of B, which of the following is true?

(a) A is the limiting reactant because of its higher molar mass.
(b) A is the limiting reactant because you need 3 moles of A and have 2.
(c) B is the limiting reactant because you have fewer moles of B than A.
(d) Neither reactant is limiting.
(e) More information is needed to determine the limiting reactant in this example.

5. The interaction between solute particles and water molecules, which tends to cause a salt to fall apart in water, is called

Short answer:
6. Provide names for the following compounds. (12 points)

(a) Na₂Cr₂O₇
(b) MnO₂
(c) PCl₅

7. Provide chemical formulas that correspond to the following compound names. (12 points)

(a) sulfur hexafluoride
(b) potassium carbonate
(c) iron (II) sulfate

8. How many protons and neutrons are in ? How many electrons are in a neutral atom of chlorine? How many electrons are in the ion formed by chlorine? (8 points)

9. Balance the following chemical equations. (8 points)

(a)

Ca(OH)2

+

H3PO4

H2O

+

Ca3(PO4)2

(b)

NaCl

+

H2O

Cl2

+

H2

+

NaOH

10. Hexamethylenediamine (C₆H₁₆N₂) is one of the starting materials for the production of nylon. It can be prepared from adipic acid (C₆H₁₀O₄) by the following reaction. (12 points)

C6H10O4

+

2 NH3

+

4 H2

C6H16N2

+

4 H2O

What mass of hexamethylenediamine can be produced from 176.5 g C₆H₁₀O₄, 198.3 g ammonia (NH₃), and 134.6 g hydrogen (H₂)?

11. Using your theoretical yield calculated in question 10, what is the percent yield for this reaction if you obtained 100.5 g of hexamethylenediamine (C₆H₁₆N₂)? (4 points)

12. A compound contains 47.08% carbon, 6.59% hydrogen, and 46.33% chlorine by mass; the molar mass of the compound is 153 g/mol. What are the empirical and molecular formulas of the compound? (10 points)

13. The density of osmium (the densest metal) is 22.57 g/cm³. (8 points)
(a) What is the mass of a block of osmium with dimensions 5.00 cm x 4.00 cm x 2.50 cm?
(b) What volume would be occupied with 1.00 kg of osmium?

14. Experimental discoveries required changes in atomic theory after Dalton first presented his theory about atoms. Describe the discoveries of Thomson, Millikan, and Rutherford and explain how our theory of atoms was changed in order to explain the new data.