Question

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

Answer 1

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.