Things to Watch For

Blackline Master U3.Q

Name: ______Date:______

Unit 3 Quiz

For each question, select the best answer from the four alternatives.

1. Which of the following statements is the best description of the law of definite proportions?

(a) A reaction always has the same mole ratio between reactants and products.

(b) A compound always has the same proportion of elements by mass.

(d) Two compounds can have the same empirical formula.

2. A reaction should produce 45.0 g of product. If only 35.0 g of product is collected, what is the percentage yield of the reaction?

(a) 28.6 %(b) 35.0 %

3. The molar mass of carbon is 12.01 g/mol, and the molar mass of hydrogen is 1.01 g/mol. Which
of the following is the molecular formula of a compound that has an empirical formula of CH2 and
a molar mass of 70.15 g/mol?

(a) C4H22(b) C4H8

Indicate whether each statement is true or false. If you think the statement is false, rewrite
it to make it true.

4. The actual yield is calculated from the given amounts of reactants, using stoichiometry.

5. High sodium levels can cause a person to retain water, which can lead to high blood pressure.

6. The coefficients in a balanced chemical equation represent the ratio of the masses of the substances.

7. The presence of side reactions lowers the theoretical yield of a chemical process.

8. Both quantitative and qualitative analyses are required to determine the percentage yield of a reaction.

9. The number of atoms of oxygen in 2.0 mol of oxygen gas, O2, is greater than the number of atoms of oxygen in 30.0 g of water, H2O.

Name: ______Date:______

Unit 3 Quiz(continued)

Match each term on the left with the most appropriate description on the right.

10. _____ (a) limiting reagent(i) Some of this substance remains at the end of a reaction.

_____ (b) Avogadro's constant (ii) This number states the mass, in grams, of one mole of a substance.

_____ (c) excess reagent(iii) None of this substance remains at the end of a reaction.

_____ (b) molar mass(iv) This number states the number of entities in one mole
of a substance.

Write a short answer to each question.

Molar masses
carbon / 12.01 g/mol
hydrogen / 1.01g/mol
oxygen / 16.0 g/mol
iron / 55.8 g/mol

11. Using the information in the chart above, how many hydrogen atoms are in 4.67 g of sucrose, C12H22O11?

12. A hydrocarbon is found to be 84.4 % carbon. What is the empirical formula of the hydrocarbon?

13. Iron can be produced from the following reaction:Fe2O3(s) + 3 CO(g)  2 CO2(g) + 2 Fe(s).

How many grams of iron(III) oxide could react completely with 459 g of carbon monoxide?

14. What is the theoretical yield of iron if 65.9 g of carbon monoxide and 98.7 g of iron(III) oxide are allowed to react?