CHEM 120 Chemical Compound and Reactions - Full Solutions

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1.How many N atoms are present in a 4.99ng sample of nitrobenzene, C6H5NO2?
Answer: 2.44*10^13

2. If 12.55g of a pure element contains 3.767 x 10^22 atoms, what is the element?
Answer: Hg


3. What mass of O is found in 37.5g Al2(SO4)3?
Answer: 21.0g


4. Complete combustion of 7.194g of a particular hydrocarbon yielded 23.41g CO2  and 7.188g of H2O. What is the empirical formula of this hydrocarbon?
Answer: C2H3


5. A 2.4385-g sample of a hydrate of Cu(NO3)2 was heated to drive off all of the water of hydration. The remaining solid weighed 1.8930g. If  Cu(NO3)2. x H2O represents the formula of the hydrate, then what is the value of x?
Answer: 3


6. How many grams of H3PO4 are produced if the following reaction yielded 23.5g HCl?
Answer: 12.6g


7. What is the minimum mass of oxygen, in grams, needed to burn 21.4g C4H10O?
Answer: 55.2g


8. What is the maximum mass of P4 that can be obtained from 74.9 g Ca3(PO4)2, 58.1g SiO2 and excess carbon? Given the balanced chemical equation: 2Ca3(PO4)2(s) + 6SiO2 + 10C(s)  -->  P4(g) + 6CaSiO3(l) + 10CO(g)
Answer: 15.0g


9. What is the molarity of C5H10O5  in an aqueous solution that is prepared by dissolving a 16.23g sample of impure C5H10O5 in water to make 1,200mL of solution. Assume that the sample is 85% C5H10O5 by mass.
Answer: 0.0766mol/L

10. An aqueous stock solution is 71.0% HClO4 by mass and its density is 1.68 g/mL. What volume of this solution is required to make 1.00 L of 2.05 mol/L HClO4(aq)? Give your answer in millilitres.
Answer: 173mL

11. What is the minimum volume of 2.61 mol/L HCl(aq) required to dissolve 15.5 g Ca metal? The atomic weight of Ca is 40.08 g/mol. The unbalanced chemical equation for the reaction is
Ca(s) + HCl(aq) --> CaCl2(aq) + H2(g)
Answer: 0.296L


12. What volume of 1.63 mol/L H2SO4(aq) is required to completely neutralize 45.1mL of 1.33mol/L KOH(aq)? Give your answer in mL.
Answer: 18.4mL


13. A sample of indium chloride, InCl3, is known to be contaminated with sodium chloride, NaCl. The contaminated sample weighs 2.74g. When the contaminated sample is treated with excess AgNO3(aq), 5.55 grams of AgCl(s) are obtained. What is the percentage by mass of InCl3 in the sample?
Answer: 84.1%