K6: Unit Study Guide/Equation Review Sheet/Stoichiometry Sample Problems
· VOCABULARY/CONCEPTS
It is likely that questions concerning vocabulary will take the form of multiple choice or matching questions.
· You must be able to balance any equation to conform to the Law of Conservation of Mass given the chemical formulas of the reactants and products. This will involve supplying coefficients when necessary while leaving subscripts unchanged.
· You must be able to determine the type of reaction (synthesis/direct combination, decomposition/analysis, single replacement, double replacement) given the chemical formulas of the reactants and products.
· Given the relative activities of elements, you should be able to determine if a single replacement reaction will take place.
· You must show that you understand the conditions for a double replacement reaction to take place (formation of a gas, formation of water, formation of a precipitate) given solubility data and the understanding of which elements form diatomic gas molecules (for example, hydrogen, nitrogen, oxygen, fluorine, chlorine)
· Given an interpretation or word equation and the naming compounds flow sheet, you should be able to write the formulas of reactants and products of an unbalanced equation.
On a separate sheet of paper do the following for each reaction:
a) State whether the equation represents a synthesis (S), decomposition (D), single replacement (SR), or double replacement (DR) reaction.
b) Balance any reactions that need to be balanced.
c) If the equation represents a single or double replacement reaction, use the activity of elements chart in your packet (SR reactions), the solubility chart in your packet, and the conditions that must be satisfied (DR reactions) to determine if a reaction will (or will not ) occur. State the reason for how you know. Remember that knowing whether a product substance is a solid, liquid, gas, or an aqueous solution is very important. Don’t forget to use your ion charge sheet or the chart on page 155 if you forget how to name the ions.
1. CO(g) ® C + O2
2. FeCl3 (aq) + AgNO3 (aq) ® Fe(NO3)3 + AgCl
3. Al + Cl2 ® AlCl3
4. BaCl2(aq) + NaOH(aq) ® NaCl + Ba(OH)2
5. ZnSO4(aq) + Cu(s) ® Cu2SO4 + Zn
6. CH4 ® C + H2
7. Pb(NO3)2(aq) + Mg(s) ® Mg(NO3)2 + Pb
8. MgCl2(aq) + H2(g) ® HCl + Mg
9. H2SO4 ® H2 + S + O2
10. O2 + N2 ® N2O4
11. CaBr2(aq) + NaNO3(aq) ® Ca(NO3)2 + NaBr
12. KI +Br2 ® KBr + I2
13. C6H12O6 ® C + O2 + H2
14. NaF ® Na + F2
15. Si + Cl2 ® SiCl4
16. Na(C2H3O2)(aq) + Pb(NO3)2(aq) ® Pb(C2H3O2)2 + NaNO3
17. NaI(aq) + Ca(s) ® CaI2 + Na
18. H2 + CO + O2 ® H2CO3
19. Li3PO4 ® Li + P + O2
20. AlI3(aq) + Br2(l) ® AlBr3(aq) + I2(s)
STOICHIOMETRY SAMPLE PROBLEMS/QUESTIONS:
The following statements and definitions match vocabulary and concepts that we have discussed in this stoichiometry unit. Your answers to these should be short. You may use this with the Unit F study guide for the Unit F test on Stoichiometry.
1. In a balanced chemical equation, the coefficients represent:
______
2. What is Avogadro’s Hypothesis? ______
3. What is standard temperature and pressure (STP)? ______
4. What is the molar volume of a gas at standard temperature and pressure?______
5. What is a limiting reactant? ______
6. What is an excess reactant? ______
7. Given the following balanced chemical equation:
2NaCl (s) ® 2Na (s) + Cl2 (g)
How many moles of Cl2 are produced from 6.7 moles of NaCl?
8. Given the following balanced chemical equation for a reaction taking place at STP:
2CO (g) + O2(g) ® 2CO2 (g)
How many liters (@ STP) of CO2 (g) can be produced from 3 L O2?
9. Consider the following balanced chemical reaction equation that describes the reaction between silver metal and nitric acid, HNO3, and answer the questions on a separate piece of paper:
3 Ag (s)+ 4 HNO3 (aq) ® NO (g) +3 AgNO3 (aq) + 2 H2O (l)
GIVEN: 43.3 grams of silver metal, Ag, are reacted with 43.3 grams of nitric acid, HNO3:
A) Write the recipe for this reaction, including moles, mass, and volume where necessary. Make sure you show all calculations as to how you got your values for mass and volume.
B) Is there an excess of either reactant? If yes, which one? You must show work to support your response.
C) How many moles of water are formed from these reactants (Remember to use the given amount of the limiting reactant)?
D) What volume of nitrogen (II) oxide gas, NO (g), is formed if the reaction occurs at STP?
10. Zinc metal, Zn (s), reacts with dilute hydrochloric acid, HCl (aq) to yield aqueous zinc chloride, ZnCl2(aq) and hydrogen gas, H2 (g).
A) Write the chemical reaction equation and balance it.
B) Write the recipe for this reaction, including moles, mass, and volume where necessary. Make sure you show all calculations as to how you got your values for mass and volume..
C) If you have 12.35 grams of hydrochloric acid, HCl, how many moles of zinc metal are required to completely use up the acid in the reaction?
D) If you have 12.35 grams of HCl, what volume of hydrogen gas, H2 should be produced if the reaction occurs at STP?
E) What is the maximum mass of ZnCl2 you can expect to produce if you have 25.0 grams of HCl? (Assume that you have plenty of zinc metal to react with the HCl.)
F) If only 36.7 grams of ZnCl2 is produced from 25.0 grams of HCl, what is the percent yield of this reaction?
G) How many molecules of HCl are needed to produce 15.3 g of ZnCl2?
ANSWERS TO FILL-INS AND PROBLEMS:
1. relative number of particles of reactants and products, relative number of moles of reactants and products, relative volumes of reactant and product gases if the reaction occurs at constant temperature and pressure.
2. Identical volumes of gases held at equal temperatures and pressures will have the same number of particles (atoms, molecules)
3. 0°C (or 273 K) and 101.3 kPa (or 1 atm, 14.7 psi, or 760 mm Hg)
4. 1 mole of a gas @ STP = 22.4 dm3 (L) of gas
5. It stops the reaction because it is used up before the other reactant(s).
6. It is not completely used up during the reaction—there is some left over.
7. 2NaCl (s) 2Na (s) + Cl2 (g) 6.7 mol NaCl ® ? mol Cl2
2 mol NaCl = 2 mol Na = 1 mol Cl2 =3.4 mol Cl2 (SF=2)
8. 2CO (g) + O2(g) ® 2CO2 (g) 3 L O2 ® ? L CO2 @ STP
2 L CO = 1 L O2 = 2 L CO2 (@ same T,P) = 6 L CO2
9. 3 Ag (s) + 4 HNO3 (aq) ® NO (g) +3 AgNO3 (aq) + 2 H2O (l)
A) RECIPE:
3 mol Ag 4 mol HNO3 1 mol NO 3 mol AgNO3 2 mol H2O
323.7 g Ag 252.0 g HNO3 30.0 g NO 509.7 g AgNO3 36.0 g H2O
@ STP: 22.4 L NO
B) 43.3 g Ag ® ? g HNO3 OR 43.3 g HNO3 ® ? g Ag
= 33.7 g HNO3 OR = 55.6 g Ag (so HNO3 IS IN EXCESS)
C) 43.3 g Ag ® ? mol H2O = 0.267 mol H2O are produced
D) 43.3 g Ag ® ? L CO @ STP = 3.00 L CO @ STP are produced
10. A) Zn (s) + 2 HCl (aq) ® H2(g) + ZnCl2(aq)
B) RECIPE:
1 mol Zn 2 mol HCl 1mol H2 1 mol ZnCl2 aq
65.4 g Zn 73.0 g HCl 2.0 g H2 136.4 g ZnCl2
6.02(10)23atoms Zn 1.204(10)24molecules HCl 6.02(10)23molecules H2 6.02(10)23formula units ZnCl2
@ STP: 22.4 L H2
C) = 0.169 mol Zn / D) = 3.79 L H2E) = 46.7 g ZnCl2 / F) % Yield = = 78.6 % YIELD
G) = 1.35´1023molecules HCl required