Note: there are 5 points of extra credit built in to this exam. 1. (4 points) For each of the following element categories, give three examples.

Transcription

1 Exam 1 Chem 1A, Fall 2016 Fossum Name: Note: there are 5 points of extra credit built in to this exam. 1. (4 points) For each of the following element categories, give three examples. a. noble gases b. inner-transition elements c. elements in the 4 th period d. nonmetals 2. (2) State whether each of the listed properties is a physical property or a chemical property. a. Sulfur is a bright yellow solid. b. Sulfur can be burned in oxygen. c. Sulfur reacts with all of the elements except for gold, platinum, iridium, nitrogen, tellurium, iodine, and the noble gases. d. Sulfur is insoluble in water. 3. (2) Perform the following calculation and round the result to the appropriate number of digits. No points if the number of sig figs is incorrect. ( ) 100 = (3) If sodium metal reacts with oxygen gas to form an ionic compound, a. What is the formula of the compound? b. Write and balance the equation for the reaction. 1

2 5. (2) If the empirical formula of a compound is NPCl 2 and it has an approximate molar mass of 350 g/mol, what is the molecular formula of the compound? (Just to be clear, this compound contains chlorine, not carbon and iodine.) 6. (6) Name each of the following compounds. (Spelling counts!) Na 2 C 2 O 4 PBr 3 H 2 SO 3 Fe(NO 2 ) 3 HF Hg(IO 4 ) 2 7. (6) Write formulas for each of the following compounds. gold (III) permanganate acetic acid carbon tetrachloride lead (II) phosphate calcium nitride bromic acid 8. (3) Convert 72 F (a nice, sunny, not-too hot day) to C and to kelvins. 2

3 9. (2) a. What was determined in JJ Thomson s experiment on cathode ray tubes? b. What was determined in Millikan s oil drop experiment? c. What was calculated by combining information from the above two experiments? 10. (4) What did Rutherford s experiment (shooting alpha particles through thin gold foil) reveal about atomic structure? HOW? Explain the evidence. (Include only things revealed by this experiment. Don t include things that were learned later on.) 11. (4) Explain the differences between mixtures and pure substances, and give two examples of each. 12. (4) a. How many protons, electrons, and neutrons are in the following: 107 Ag? b. If you had an isotope of 107 Ag, how would it be similar and how would it be different from 107 Ag? 3

4 13. (5) Draw molecular pictures of each of the following. Show atoms as circles, and atoms of different elements using different colors or shading. (Show at least 6 molecules in each picture.) Briefly explain each drawing. a. A homogeneous mixture of two elements in the liquid phase. b. A compound in the gas phase. 14. (4) a. Explain the difference between accuracy and precision. b. If you are making measurements with a miscalibrated scale, what is the effect on the experimental results accuracy? (For example, what if a ruler had markings that were offset from the end of the ruler?) How will this affect the precision of the results? 15. (5) Precious metals and gems are measured in troy weights in the English system. Gold has a density of 19.3 g/cm 3. What is the volume of 2.00 troy ounces of gold? 24 grains = 1 pennyweight (exact) 20 pennyweights = 1 troy ounce (exact) 1 grain = gram 4

5 16. (10) Ag (s) + S 8 (s) Ag 2 S (s) a. Classify this type of reaction. b. When 35.0 grams of silver is mixed with excess sulfur and allowed to react, what mass of silver sulfide will be obtained in theory? c. If 34.2 grams of silver sulfide are actually obtained after the above reaction, calculate the percent yield of this reaction. d. Is this percent yield lower or higher than 100%? What are some possible reasons for this? 17. (12) Write the molecular equation, the complete ionic equation, and the net ionic equation for each of the following reactions. a. (NH 4 ) 2 CO 3 (aq) + Cr(C 2 H 3 O 2 ) 3 (aq) 5

6 (continued... write the molecular equation, the complete ionic equation, and the net ionic equation) b. LiOH (aq) + H 3 PO 4 (aq) 18. (6) Write the net ionic equation (only) for each of the following reactions. a. K 2 CO 3 (aq) + HI (aq) b. NaI (aq) + Pb(NO 3 ) 2 (aq) 19. (12) For the following reaction: C (s) + Fe 2 O 3 (s) Fe (s) + CO (g) a. If you combine 15.0 grams of carbon and 15.0 grams of iron (III) oxide and allow them to react, what mass of carbon monoxide should be obtained in theory? 6

7 b. What mass of the excess reactant will be left over? (see part a.) For the following problem, if you do better on this question than you did on the similar question on Quiz 3, you will get some more points applied to quiz 3. (It s not extra credit, it s a re-do. Do not skip this problem.) 20. (9) An unknown organic compound that contains carbon, hydrogen, and oxygen is burned in air. When grams of the compound is burned, the products are grams of carbon dioxide and grams of water. Determine the empirical formula of this compound from this information. (Note: if you can t figure out how to do this problem, then do the following problem instead.) 7

8 Note: only do this problem if you can t figure out how to start the previous problem. It is worth fewer points. Do not do both. 20 (alternate) (5) An unknown compound is 36.14% carbon, 8.49% hydrogen, % nitrogen, and % oxygen by mass. Determine the empirical formula of this compound. 8