CHM 102 Test #1, answers 1) (1 pt. each) For each of the following terms, please provide a definition of the term as it is used in science. a) Hypothesis A hypothesis is a question or prediction that is the basis of an experiment. Feynman’s “guess”: “I think this will happen. Let’s see…” b) Theory An explanation of some phenomenon, backed up by a great deal of evidence. c) Law A description of some phenomenon, backed up by a great deal of evidence. 1 CHM 102 Test #1, answers 2) (1 pt. each) Tell me two sorts of things science cannot provide answers about. Too many to list here, sorry. 3) (1 pt.) Iron reacts with oxygen to give iron oxide (rust). You started out with 12 grams of iron, and ended with 16 grams of iron oxide. What is the mass in grams of the oxygen that reacted with the iron? You started with 12 grams of iron and some amount of oxygen, and you end up with 16 grams of iron oxide. 16 – 12 = 4 grams of oxygen. 4) (1 pt.) Ethanol reacts with oxygen (i.e. it burns) to produce carbon dioxide and water (you start with ethanol and oxygen, you end up with carbon dioxide and water). If you react 230 grams of ethanol with 480 grams of oxygen, what is the combined mass of carbon dioxide and water that you end up with? You start with 230 grams of ethanol and 480 grams of oxygen, so the total mass of what you end up with is 230 + 480 = 710 grams. 2 CHM 102 Test #1, answers 5) (2 pts.) When you break 1668 grams of phosphorus pentachloride down into its elements, you get 248 grams of phosphorus and 1420 grams of chlorine. When you break 417 grams of phosphorus pentachloride down, how many grams of phosphorus and how many grams of chlorine do you get? I will use the abbreviations “PCl5“ for phosphorus pentachloride, “P” for phosphorus, and “Cl” for chlorine. Simplify the problem: -­‐ If you start with 1668 g PCl5, you get 248 g P and 1420 g Cl. -­‐ If you start with 417 g PCl5, you get how much P and how much Cl? 1668 / 417 = 4, so 1668 / 4 = 417. I divide by 4 to go from the first case to the second case. 248 g P / 4 = 62 g P 1420 g Cl / 4 = 355 g Cl Check your answer: If you start with 417 g PCl5, you end with 62 g P and 355 g Cl. We start with less PCl5, so we expect less P and Cl, and we see that here. Also, the mass you start with must equal the mass you end with: 417 = 62 + 355, so this answer looks plausible. 3 CHM 102 Test #1, answers 6) (5 pts.) What are the five parts of Dalton’s Atomic Theory of Matter? 1. All matter is made up of atoms. 2. Atoms cannot be created, destroyed, or divided. 3. All the atoms of an element are (essentially) the same. 4. Atoms of different elements are different. 5. Atoms can combine to form compounds. 7) (1 pt.) The atomic number of an element is the number of __protons__ in an atom. 4 CHM 102 Test #1, answers 8) (1 pt.) The mass number of an atom is the number of __ protons and neutrons ___ in that atom. 9) (1 pt.) What is the atomic mass of bismuth? 208.9804. You must include all the digits for credit on this: you do not get to just lop off digits you don’t want to include. 10) (12 pts.) Please fill in the following table of properties. Neutrons Electrons Protons Location (inside or outside of Inside Outside Inside nucleus) 0.00055, or Approximate mass 1 1/1810, or zero, or 1 in amu “very small” Charge When you change the number of these particles, what is the major thing that also changes? 0 -­‐1 +1 Mass and thus the isotope Charge Element 11) (1 pt. each) How many protons are in an atom of: a) Krypton ___ 36 ___ b) Carbon ___ 6 ___ c) Antimony ___ 51 ___ d) Potassium ___ 19 ___ 5 CHM 102 Test #1, answers 12) (3 pts. per row) Please fill in the following table. Number of Number of Atom specifier protons neutrons !"
!"Kr
Number of electrons 36 49 36 ! !
!H 1 0 0 !" !!
!N 7 6 10 81 124 80 3 3 3 33 42 36 !"#
!
!"
Tl! Li
As !! Note: I did not include the atomic number in the atom specifiers in the last three rows because they are really optional and so I did not grade on them. 6 CHM 102 Test #1, answers 7