CHEMICAL REACTION I
UNIT 3 CHEMICAL REACTIONS
ANSWER KEY
Friday, March 4, 2011
Name: ______
AHS Instructor Ms. Kasia Room 109
TOTAL POINT / /35PART A / /16
PART B / /19
BONUS / /2
Part A
Answer all questions in this part.
Directions (1-16): For each statement or question, circle the number of the word or expression that, of those given, best completes the statement or answers the questions. Some questions may require the use of the Reference Tables for Physical Setting/ Chemistry. [16 points]
Question (0.5pts each) / Explanation (0.5pts each)1. Which phrase best describes an atom?
(1) a positive nucleus surrounded by a hard negative shell
(2) a positive nucleus surrounded by a cloud of negative charges
(3) a hard sphere with positive particles uniformly embedded
(4) a hard sphere with negative particles uniformly embedded / The electrons surround the positive nucleus (protons and neutrons) in orbitals.
2. All chemical reactions have a conservation of
(1) mass, only
(2) mass and charge, only
(3) charge and energy, only
(4) mass, charge, and energy
3. Which two particles have opposite charges to one another?
(1) electron and neutron
(2) neutron and positron
(3) proton and electron
(4) proton and neutron / Protonsà +
Electrons à -
4. Which equation shows conservation of atoms?
(1) Na + O2 à Na2O
(2) 2Na + O2 à 2Na2O
(3) 4Na + O2 à 2Na2O
(4) 4Na + 2O2 à 2Na2O
5. Compared to an electron in the fourth electron shell of an atom, an electron in the first shell of the same atom has
(1) less mass
(2) less energy
(3) more mass
(4) more energy
6. What is the gram-formula mass of Al2(SO3)3?
(1) 75 g/mol
(2) 246 g/mol
(3) 294 g/mol
(4) 402 g/mol
7. What is the total number of neutrons in an atom of an element that has a mass number of 23 and an atomic number of 11?
(1) 23
(2) 11
(3) 12
(4) 6
8. Given the balanced equation:
2 S + 3 H2 à 2SH6
What is the total number of moles of S that must completely react to produce 4.0 moles of SH6?
(1) 1.0 mol
(2) 2.0 mol
(3) 3.0 mol
(4) 4.0 mol
9. Which metal reacts spontaneously with a solution containing calcium ions?
(1) fluorine
(2) nickel
(3) copper
(4) barium
10. Which equation represents a double replacement reaction?
(1) 2 Na + 2 H2O à 2 NaOH + H2
(2) LiBr (s) à Li (aq) + Br (aq)
(3) NaOH + HCl à NaCl + H2O
(4) C3H8(g) + 5O2(g) à 16CO2(g) + 18H2O(l)
11. Given the balanced equation representing the reaction between propane and oxygen:
2CH3OH + 3 O2 à 2 CO2 + 4 H2O
According to this equation, which ratio of O2 to CH3OH is correct?
(1) (3)
(2) (4)
12. What is the percent composition by mass of sulfur in Al2(SO4)3 (gram formula mass = 342 grams/mole)?
(1) 9.38%
(2) 15.8 %
(3) 28.13%
(4) 36.0 %
13. Which equation shows a conservation of mass?
(1) Na + Cl2 à 2NaCl
(2) 2B + 3Br2 à 2BBr3
(3) 3H2O à H2 + O2
(4) PCl5 à PCl3 + 2Cl2
14. Given the balanced equation representing a reaction:
2 H2O (l) + Ni2 (s) à 2 NiO2 (aq) + 2H2 (g)
What is the mole ratio of H2O (l) to NiO2 (aq) in this reaction?
(1) 1:1
(2) 1:2
(3) 2:1
(4) 3:2
15. Which formula represents copper (II) nitrate?
(1) Cu(NO3)2
(2) Cu(NO2)2
(3) Cu(NO3)
(4) Cu(NO2)
16. Given the balanced equation:
C2H5OH (l) + 3 O2 (g) à 2 CO2 (g) + 3 H2O (l)
What is the total number of moles of O2 (g) that must react completely with 5.00 moles of C2H5OH(g)?
(1) 1.0
(2) 10.0
(3) 5.0
(4) 15.0
Part B
Answer all questions in this part.
Directions (17-): Record your answers in spaces provided in your answer booklet. Some questions may require the use of the Reference Tables for Physical Setting/Chemistry. [19 points]
17. “Hand Blasters” is a toy that consists of a set of two ceramic balls, each coated with a mixture of sulfur and potassium chlorate, KClO3. When the two balls are struck together, a loud popping noise is produced as sulfur and potassium chlorate react with each other.
a) Balance the equation for the “Hand Blaster” reaction, using the smallest whole-number coefficients.
3 S(s) + 2 KClO3(s) à 3 SO2(g) + 2 KCl(s) + energy
18. During a laboratory activity, a student reacted a piece of silver with 0.1 M HCl (aq).
a) Complete the equation below by writing the formula of the missing product.
Ag (s) + 2 HCl (aq) à AgCl (aq) + H2 (g)
b) Balance the formula above.
2 Ag (s) + 2 HCl (aq) à 2 AgCl (aq) + H2 (g)
c) What type of reaction is this?
This is an example of a single replacement reaction
d) Based on Reference Table J, identify one metal that spontaneously reacts with HCl.
Any element listed above Hydrogen on Table J will spontaneously react with HCl.
19. The particle diagrams below represent the reaction between two chemicals, a nonmetal A2 and a metal Q2.
a) Using the symbols A and Q, write the chemical formula of the product.
AQ3
b) Identify the type of chemical bond between an atom of element A and an atom of element Q.
Since A2 is a nonmetal and Q2 is a metal, when they bond they will form an ionic bond.
c) Compare the total mass of the reactants to the total mass of the product.
The total mass of the reactants equals to the total mass of the products, according to the law of conservation of mass.
20. What is the total number of moles in 150.0 grams of C2H5Cl (gram-formula mass= 64.5 grams/mole)?
Moles = grams given/gram-formula mass
= 150.0g /64.5g
=
21. What is the mass of 9.52 moles of Na3PO4 (gram-formula mass = 164 grams/ mole)?
Moles = grams given/gram-formula mass
9.52moles = x /64.5g
X =(9.52)(64.5) =
22. You are able to create a volcanic explosion for a science fair project through the decomposition of hydrogen peroxide, H2O2(aq), into water, H2O(l), and oxygen O2(g). This is the chemical equation:
H2O2(aq) à H2O(l) + O2 (g)
a) Write the balanced equation below.
2H2O2(aq) à 2 H2O(l) + O2 (g)
b) How many moles of O2 is produced when 20 grams of H2O2(aq) is reacted?
H2O2 H2O O2
2 :2 :1
20g ?
1. Moles = (20g)/(gram-formula mass of H2O2)
2. See how many moles of O2 can be produced
23. Archimedes (287-212 BC), a Greek inventor and mathematician, made several discoveres important to science today. According to a legend, Hiero, the king of Syracuse, commanded Archimedes to find out if the royal crown was made of gold, only. The king suspected that the crown consisted of a mixture of gold, tin, and copper.
Archimedes measured the mass of the crown and the total amount of water displaced by the crown when it was completely submerged. He repeated the procedure using individual samples, one of gold, one of tin, and one of copper. Archimedes was able to determine that the crown was not made entirely of gold without damaging it.
a) Identify one physical property that Archimedes used in his comparison of the metal samples.
Archimedes used density to compare the metal samples.
b) Determine the volume of a 90-gram sample of gold at STP.
Density= mass/volume
= 90g/x
X=
(can get density from Table S)
24. Base your answer to 28a and 28b on the balanced equation below.
Mn(s) + 2HNO2(aq) à Mn(NO2)2(aq) + H2(g)
a) What is the total number of oxygen atoms represented in the formula of the Manganese compound produced?
4
b) Explain, using information from Reference Table J, why this reaction is spontaneous.
This reaction is spontaneous since Mn is located above H, indicating that it has a higher reactivity.
BONUS: 1. How can you identify that a chemical reaction took place? Color change, gas, precipitate
2. What is the name of the phase change when gas turns back into liquid? condensation