Problem Set #10 - Answers

Transcription

1 Problem Set #10 - Answers BIG IDEAS Fill in the blanks or circle the correct response in brackets. 1) When a reaction occurs, the stuff you start with is called the _reactants_ and the stuff you end up with is called the _products_. 2) Chemical reactions involve breaking some of the _bonds in the reactants and forming new _bonds_ to make the products. 3) Certain elements, when on their own, always form diatomic molecules. Known as the 7+1 club, these include: H 2, N 2, O 2, F 2, Cl 2, Br 2, I 2, and At 2 (even though At 2 doesn t exist, I m including it because it makes the 7 th member of the 7 shape on the periodic table.) Problems: 4) Use the unbalanced chemical equation below to answer the questions that follow. 4_ Al(s) + 3 O 2 (g) _2 Al 2 O 3 (s) (a) In what state of matter is the reactant aluminum? solid (b) Balance the equation by including the coefficients above. (c) Why is the ratio of aluminum atoms to oxygen atoms in the product 2 to 3? How could you have predicted this ratio? Aluminum oxide is held together by ionic bonding. Aluminum atoms have three valence electrons each. Therefore, they will lose all three and form ions with a 3+ charge. Oxygen atoms have 6 valence electrons each. Therefore, they will gain two (to make a total of eight) to form ions with a 2- charge. In order to balance out, we need to put two aluminum ions together with every three oxygen ions. (d) (circles = O atoms, triangles = Al atoms) 5) Use the chemical equation below to answer the questions that follow. C 11 H 24 (l) + 17 O 2 (g) 11 CO 2 (g) + 12 H 2 O(l) (a) What does the (g) after O 2 indicate? Answer in a complete sentence. Oxygen is a gas in this reaction. (b) What does the 11 before CO 2 indicate? Answer in a complete sentence. There are 11 separate carbon dioxide molecules produced in this reaction for every 1 molecule of C 11 H 24 that reacts. The coefficients tell you the ratio of separate molecules of each substance involved in the reaction. (c) What do the 11 and the 24 in C 11 H 24 indicate? Answer in a complete sentence. These numbers indicate the number of atoms of each element bonded together in one molecule of a substance. So in this case, there are 11 carbon atoms and 24 hydrogen atoms bonded together to make one molecule of this particular reactant. (d) What does the arrow ( ) indicate? Answer in a complete sentence. The arrow indicates that the reactants on the left produce the products on the right when allowed to react.

2 6) Cation Anion Formula Name Fe 2+ Cl FeCl 2 iron (II) chloride Na + Br NaBr sodium bromide Al 3+ S 2 Al 2 (SO 4 ) 3 aluminum sulfide Ca 2+ I CaI 2 calcium iodide Al 3+ Cl AlCl 3 aluminum chloride Ga 3+ S 2 Ga 2 S 3 gallium sulfide Li + Te 2 Li 2 Te lithium telluride Rb + Cl RbCl rubidium chloride Al 3+ O 2 Al 2 O 3 aluminum oxide Mg 2+ N 3 Mg 3 N 2 magnesium nitride 7) Use the balanced chemical equation below to answer the questions that follow. C 2 H 4 (g) + Br 2 (l) C 2 H 4 Br 2 (l) (a) Draw Lewis dot structures for the reactants and products. (b) What bonds in the reactants must break in order to make the products? The single bond between the two Br atoms and one of the two bonds in the double bond between the two C atoms must break (see above). (c) What new bonds must be created in order to make the products? Two new bonds between C and Br must be formed (see above). (d) Draw a particulate diagram of the reactants and products in this reaction. Include at least 3 molecules of each reactant, and be sure to follow the law of conservation of matter. [Here is an older phrasing of the question with a different looking answer. I m leaving it in here in case you find the answer useful.] Using circles to represent atoms, draw what is happening at the molecular level during this reaction. Note: There are lots of different things you could have drawn here. I just want you to have the idea that the reaction involves rearrangement of the way the atoms are bonded together. I used different sizes to represent the atoms, because atoms get larger as you move down the periodic table.

3 8) Balance each of the following chemical equations. (a) 1 C 3 H O 2 3 CO H 2 O (b) 1 (NH 4 ) 2 Cr 2 O 7 1_ N Cr 2 O H 2 O (c) 1_ CaO + 1 SO 3 1 CaSO 4 (d) 2 N 2 O 5 4 NO O 2 (e) 2 C 7 H 16 O O 2 14 CO H 2 O (f) _2 AgNO Ni 2 Ag + 1 Ni(NO 3 ) 2 (g) 3 BaBr K 3 PO 4 1 Ba 3 (PO 4 ) KBr combustion (you don t need to know) decomposition combination decomposition combustion (you don t need to know) single exchange double exchange

4 9) Draw a particulate diagram for reaction (f) above. Include at least 3 atoms of Ni(s), and be sure to follow the law of conservation of matter. The Ag + and NO 3 ions should be separated and floating around in the before picture. The Ni atoms should be together as a solid in the before picture. The Ag atoms should be together in a solid in the after picture. The Ni 2+ and NO 3 ions should be separated in the after picture. The ratios must be the same as in the equation. 10) Draw a particulate diagram for reaction (g) above. Include at least 6 formula units of BaBr 2 (aq), and be sure to follow the law of conservation of matter. The ions in the before pictures should be separated. The Ba 2+ and PO 3 4 ions should be stuck together in a solid in the product. You should actually have twice as many ions as shown in the drawing above (someone didn t follow instructions). The ratios must be the same as in the equation.

5 11) When sodium reacts with oxygen, (a) what product would you expect to be formed? Give both the name and the chemical formula. The product would be sodium oxide, Na 2 O, because sodium atoms lose one electron each to become Na + ions, and oxygen atoms gain two electrons to become O 2 ions. (b) 4 Na(s) + O 2 (g) 2 Na 2 O(s) (c) The Na atoms should be together in a solid beforehand. The O atoms should be bonded in groups of two beforehand. The ions should be stuck together rin an alternating pattern in the product. The ratio must match the equation. 12) When zinc (II) carbonate is heated, it breaks down into carbon dioxide and zinc oxide. A video of this reaction can be viewed here: (a) Write a balanced chemical equation for this reaction. ZnCO 3 (s) ZnO(s) + CO 2 (g) (b) 13) TNT, trinitrotoluene, is a commonly used explosive. Its structure is shown below. When ignited in an enclosed space, it decomposes into carbon monoxide gas, solid carbon, nitrogen gas, and water vapor. The structure of TNT is shown to the left. Write a balanced chemical equation for this reaction. (Note: This equation may be tough to balance). 2 C 7 H 5 N 3 O 6 (s) 7 CO(g) + 7 C(s) + 3 N 2 (g) + 5 H 2 O(g)