Question

For questions 13-14, use the information provided below from the experiment Identification of an Unknown. The molecular masses and reactions are provided for you.

NaHCO₃ KHCO₃ Na₂CO₃ K₂CO₃ NaCl KCl

84.01 g/mol 100.12 g/mol 105.99 g/mol 138.21 g/mol 58.44 g/mol 74.55g/mol

2 NaHCO₃ (s) Ã Na₂CO₃ (s) + H₂O (g) + CO₂ (g) (Reaction 1)

Na₂CO₃ (s) +2HCl (aq) Ã 2NaCl (s) + H₂O (l) + CO₂ (g) (Reaction 2)

13. Brad starts with 0.652 g of unknown. How much mass should he have after the first heating step if his unknown
was NaHCO₃?

A. 0.411 g Na₂CO₃

B. 0.326 g Na₂CO₃

C. 0.822 g Na₂CO₃

D. 0.00402 g Na₂CO₃

14. If Brad has a final mass of 0.270 g at the end of the experiment (after the 2^nd heating), what is his percent yield
of the final salt? (Assuming he starts with 0.652 g of NaHCO₃).

A. 40%

B. 60%

C. 80%

D. 86%

15. What is the concentration of chloride ions in 50.0 mL of a 5.25 M solution of barium chloride?

A. 0.525 M Cl^-

B. 1.05 M Cl^-

C. 5.25 M Cl^-

D. 10.5 M Cl^-

Aqueous Solutions

16. Which of the following represents a correct precipitation reaction between sodium iodide and lead(IV) sulfate?

A. PbSO₄ (aq) + NaI(aq) Ã PbI (aq) + NaSO₄ (aq)

B. PbSO₄ (aq) + NaI(aq) Ã PbI (s) + NaSO₄ (aq)

C. Pb(SO₄)₂(aq) + NaI (aq) Ã PbI₂ (s) + Na₂SO₄ (aq)

D. Pb(SO₄)₂(aq) + NaI (aq) Ã PbI₂ (aq) + Na₂SO₄ (aq)

17. How many of the following salts would not form a precipitate in an aqueous solution?

A. one

B. two

C. three

D. four

18. What type of reaction is the following? CaCO₃ + heat à CaO + CO₂

A. Combination

B. Decomposition

C. Single Replacement

D. Combustion

19. Calculate the amount of copper recovered from an 85% yield if the theoretical yield is 0.25 g

A. 21 g

B. 3.4 g

C. 0.21 g

D. 0.34 g

20. Which of the following chemical species is the oxidizing agent in the reaction below?

Cu (s) + 4 HNO₃ (aq) → Cu(NO₃)₂ (aq) + 2 NO₂ (g) + 2 H₂O (l)

A. Cu (s)

B. HNO₃ (aq)

C. Cu(NO₃)₂ (aq)

D. NO₂ (g)