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CHM1025 Final Exam Review, Exams of Chemistry

Texas A&M University (A&M)Chemistry

Note: the molecular formula gives the actual number of atoms of each ... reactant and mass of AlBr3 produced when 45.0 g of Br2 is added to 30.0 g of Al.

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2022/2023

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CHM1025 Final Exam Review
1. How many significant figures are in the number 0.0000462?
a. 3
b. We ignore the leading zeroes!
2. Convert the following value to scientific notation: 29,600.
a.
2.96 ร—10!
.
3. Is the combustion of methane gas a physical or chemical change?
a. It is a chemical change. See the following reaction to understand how methane
changes chemically upon combustion.
4. Classify the following as an element, compound, homogeneous mixture, or
heterogeneous mixture: water
a. Compound. Water is a pure substance composed of two different elements (H and
O).
5. Classify the following as an element, compound, homogeneous mixture, or
heterogeneous mixture: instant coffee dissolved in water.
a. Homogeneous mixture (a.k.a. solution).
b. This mixture has uniform composition and properties throughout!
pf3
pf4
pf5

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CHM1025 Final Exam Review

  1. How many significant figures are in the number 0.0000462? a. 3 b. We ignore the leading zeroes!
  2. Convert the following value to scientific notation: 29,600. a. 2. 96 ร— 10 !.
  3. Is the combustion of methane gas a physical or chemical change? a. It is a chemical change. See the following reaction to understand how methane changes chemically upon combustion.
  4. Classify the following as an element, compound, homogeneous mixture, or heterogeneous mixture: water a. Compound. Water is a pure substance composed of two different elements (H and O).
  5. Classify the following as an element, compound, homogeneous mixture, or heterogeneous mixture: instant coffee dissolved in water. a. Homogeneous mixture (a.k.a. solution). b. This mixture has uniform composition and properties throughout!
  1. Name the following compound: SF6. a. Sulfur hexafluoride. b. SF6. is a nonmetal covalent compound that consists of sulfur and fluorine. c. There is one sulfur atom. There are six (hexa-) fluorine atoms. d. Since fluorine comes second in the compound, it is given the ending โ€œ-ide.โ€
  2. Balance the following equation: _NH 4 NO 3 _N 2 O + _H 2 O a. NH 4 NO 3 N 2 O + 2 H 2 O
  3. Balance the following equation: _P 4 O 10 + _H 2 O _ H 3 PO 4 a. P 4 O 10 + 6 H 2 O 4 H 3 PO 4
  4. What type of reaction is Zn + 2HCl ZnCl 2 + H 2? a. Single displacement.
  5. What type of reaction is HCl + NaOH NaCl + H 2 O? a. Double displacement.
  6. How many moles are in 5.04 g of CaCO 3? a. 0. b. Formula weight of CaCO 3 : 100.09 g/mol c. 5.04 g CaCO 3 ร— " $%&' ()(+ ",,.,. / ()(+ = 0.0504 mol CaCO 3.
  7. Part A: A laboratory analysis of an unknown compound determined the following mass percent composition of: 63.15% C, 5.30% H, and the rest O. What is the empirical formula of the compound? a. C 8 H 8 O 3 b. Note: the empirical formula gives the simplest whole-number ratio of atoms in a compound.

c. In this case, the molar mass is twice that of the empirical formulaโ€™s molar mass, so we know that we need to multiply all of the subscripts of the atoms in our empirical formula of the molecule by 2.

  1. When liquid bromine is mixed with aluminum metal, a combination reaction occurs, forming aluminum bromide: 2Al(s) + 3Br2(l) 2AlBr3(s). Determine the limiting reactant and mass of AlBr3 produced when 45.0 g of Br2 is added to 30.0 g of Al. a. LR: Br 2 ; 50.0 g AlBr 3 b. First, convert all reactant grams to moles. i. 45. 0 ๐‘” ๐ต๐‘Ÿ 2 ร— " $%& 012 "3..4. / 012 = 0. 281 ๐‘š๐‘œ๐‘™ Br 2 ii. 30. 0 ๐‘” ๐ด๐‘™ ร— " $%& 5& 26 ..4 / 5& = 1. 11 ๐‘š๐‘œ๐‘™ Al c. Next, determine how many moles of one reactant are needed to react with the other. i. 1. 11 ๐‘š๐‘œ๐‘™ ๐ด๐‘™ ร— + $%& 012 2 $%& 5& = 1. 67 ๐‘š๐‘œ๐‘™ Br2. ii. To react with all of our Al, we would need 1.67 mols of Br 2. However, we only have 0.281 mols of Br 2 , which makes it out limiting reactant. d. We must use our limiting reagent to do our final product mass calculation. i. 0. 281 ๐‘š๐‘œ๐‘™ ๐ต๐‘Ÿ 2 ร— 2 $%& 5&01+ + $%& 012

ร—

  1. 7 / 5&01+ " $%& 5&01+ = 50. 0 g AlBr 3.

  2. Draw the Lewis Structure for PCl 5.

a. b. First we need to count all valence electrons. P is in group 5A, so it has 5 valence electrons. Cl is in group 7A, so it has 7 valence electrons. We should also note that there are 5 Cl atoms. i. This gives us 5 + 7(5)= 40 valence electrons. c. Phosphorus is the least electronegative atom, so we should put it in the center of our molecule. d. Draw single bonds to the five Cl atoms connected to our central P. e. Complete the octets for all of the outer Cl atoms. f. We have used all of our valence electrons, and formal charges have been minimized.

  1. What is the molarity (M) of a solution that has 8.67 g of NaCl dissolved in 500 mL of water? a. 0.296 M. b. Molarity= moles/L. We must first find moles. c. 8. 67 ๐‘” ๐‘๐‘Ž๐ถ๐‘™ ร— $%& 89:& 34 .!! / 89:&

d. Our 0.148 mol of NaCl is dissolved in 500 mL, or 0.5 L.