In: Chemistry
18. Hydrogen gas reacts with oxygen gas to form water vapor. If 34.5 g of hydrogen gas react with 26.6 g of oxygen gas, how many grams of water vapor will be produced? 2H2(g) + O2(g) --> 2H2O(g)
20. The reaction of 22.5 g of Fe with excess of oxygen gas produced 24.2 g of Fe2O3. Calculate the percent yield.
21. Milk of magnesia contains magnesium hydroxide. Mg(OH)2 reacted with HCl to form aqueous magnesium chloride and liquid water. Write the properly balanced equation for this reaction.
22. Lithium reacted with oxygen gas to form lithium chloride. The chemical formula for lithium chloride is___________.
(A). LiO (B). LiO2 (C). Li2O3 (D). Li2O (E). Li2O4
23. In the following reaction, how many grams of sodium sulfate are needed to react with 3.08 moles of strontium nitrate? (Hint: stoichiometry mol Na2SO4: mol Sr(NO3)2 = 1 mol: 1 mol) Sr(NO3)2 (aq) + Na2SO4 (aq) --> SrSO4 (s) + 2 NaNO3 (aq) (balanced?)
24. Which of the following represents a chemical property of oxygen gas?
(A). It is gaseous at room temperature. (B). It reacts explosively with propane. (C). It is less dense than air. (D). It is colorless
18. 2H2 + O2 -> 2H2O
Turning reactants to moles:
34.5 grams of H2 * (1 mol / 2 grams) = 17.25 moles of H2
26.6 grams fo O2 * (1mol / 32 grams) = 0.83125 moles of O2
As we can see, limiting reactant is oxygen. and grams of product will be:
0.83125 moles of O2 * (2 moles of H2O / 1 mol of O2) * (18 grams/mol of H2O) = 29.925 grams of H2O
20. % yield = actual grams / theoretical grams
actual grams = 24.2 of Fe2O3
Theoretical grams:
4Fe + 3O2 -> 2Fe2O3
22.5 g of Fe * (1 mol / 55.845 g) = 0.4029 moles of Fe
0.4029 moles of Fe * (2 moles of Fe2O3 / 4 moles of Fe) = 0.20145 moles of Fe2O3
Now to grams -> 0.20145 moles of Fe2O3 * (160 g / mol) = 32.23 grams
% yield = 24.2 grams / 32.23 grams = 0.7508
21. Mg(OH)2 + 2HCl -> MgCl2 + 2H2O
22. Assuming it is lithium oxide instead of chloride, answer is Li2O
23. Sr(NO3)2 (aq) + Na2SO4 (aq) --> SrSO4 (s) + 2NaNO3 (aq) (BALANCED)
3.08 grams of Sr(NO3)2 * (1 mol / 211.63 grams) = 0.01455 moles of Sr(NO3)2
As we have a 1 on 1 stoichiometric relation:
0.01455 moles of Na2SO4 * (142.04 g / mol) = 2.0672 grams
24. It reacts explosively with propane, it is the only option regarding a chemical change.