AP Chemistry                                                   Unit 3

Chapter 3                                                               Stoichiometry and Reactions

Daily 1

 

Multiple Choice Questions

 

1.   Which one of the following elements has been selected as the current atomic weight standard?

A.O                            

B.C

C. H

D. Na

 

2.   Bromine is composed of two isotopes. One of the isotopes Br xx.x, makes up 49.7% of the total, while the other, Br 78.9, makes up 50.3% of the total. Calculate the atomic mass of Br xx.x.

A.  80.0

B. 80.9

C.  89.7

D.  78.9

 

 

3.   Four beakers, containing potassium nitrate dissolved in water, are allowed to evaporate to dryness. Beakers 1 through 4 contain 2.3, 1.91, 5.985, and 0.52 g of dry potassium nitrate. How many moles of potassium nitrate were recovered after the water evaporated?

A.  0.106

B. 0.212

C.  0.500

D.  2.35

 

4.   How many atoms of uranium (U) are present in 1 nanogram of uranium?

 

A.  2.5 x 1020

B.  0.5 x 1011

C.  2.5 x 1012

D.  0.5 x 1031

 

5.   Calculate the percent composition of Na2S2O3.

 

A.  29%Na, 4l%S, 30%O

B.  37%Na, 45%S, 23%O

C. 49%Na, 34%S, 17%O

D. 17%Na, 47%S, 36%O

 

 

 

 

 

 

6.   Two of the three forms of vitamin B6 are pyridoxine (C8H11NO2) and pvrodoxamine (C8H12N2O). Calculate the respective percentage of nitrogen in each compound.

A.8.8%, 17%

B.9.3%, 15%

C.9.1%, 18.4%

D.18%, 9.9%

 

7.   Calculate the molecular formula of a compound that has 48.8% Cd, 20.8% C, 2.62 % H, 27.8% O, and a molecular weight of 460.8 g/mol.

 

A. Cd2C8H12O8        

B. CdC4H6O4           

C. CdCHO8

D. Cd2C6H6O6

 

8.Determine the molecular formula of a compound that contains 26.7% P, 12. l% N, 6l.2% Cl. and a molecular weight of 580.
                                   

A. (PNCl)3                       

B. (PNCl2)5                     

C. (P2NCl2)5                        

 D. (PNCl2)

 

9.A 20 mg sample of Cx Hy is burned in oxygen to produce 60 mg of carbon dioxide and 32 mg of water. Calculate x and y by using these data.

 

A.2,4

B. 3.6

C. 1,4

D. 3,8

 

10. Find the empirical formula of the compound that contains 15.8% Al, 28.1% S, and 56.1% 0.

 

A.    Al2(SO4)3

B.    AlSO2

C.    AlSO

D.    Al2SO3             

 

11. Find the identity of the element X in the following equation

                       C3H6X3   +  3X2        à  3CX2     +  3H2O
A.O

B. H

C. Cl

D.Br

 

12. If 505 grams of KOH are required to completely react with 4.50 moles of sulfuric acid. How many moles of products are produced?

 

A.    9 moles               

B.    4.50 moles       

C.    13.5 moles               

D. 5.50 moles

 

13. The proper set of coefficients for the following equation are

      _C3H6O3  + _O2   à   _CO2    +   _H2O

 

A.1,3,3,3                             

B. 2,4.3,3

C.1,2,3,3

D. 1.6,6,6

 

14. The proper set of coefficients for the following equation are

                                         _AgCl + _HNO3  à _AgNO3   +   _HCl
A.1,1,1,1                             

B. 1,2,2,1                                

C.2.3.1,1   

D. 2.2,2,2

 

 

15. The proper set of coefficients for the following equation are

                                                               _C3H8   + _F2    à    _C3F8    +    _HF


A.1,8,1,8                   

B. 1,3,1,3                  

C.    2,16,2,16             

D. 1,1,1,1

 

 

16. A solution of copper sulfate is treated with zinc metal. How many grams of copper are produced if 2.9 g of zinc are consumed?

                        CuSO4 +   Zn         à     ZnSO4 + Cu

 

A.    2.9g

B.    2.8g

C.    5.7g

D. 3.7g

 

 

17. How many grams of sulfur dioxide are produced when 90.0 g of thionyl chloride reacts with excess water according to the following equation’?

                      SOCl2    +    H2O   à     2HCl     +    SO2

 

      A.96.8

 B. 90.0

C.24.2

D. 48.4

 

 

18. Calculate the number of grams of TiOCl2 required to react with 134 g of carbon.

                       2TiOC12 + 2C      à    2Ti + CO2 + CC14

 

A.    134                

B.    1.51 x l03

C.    536

D. 67

 

19.Identify the limiting reagent for the following equation if the process started with 1 gram of each reactant.

 

                    Cr2O3    +   3CC14    à  2CrC13 + 3COCl2

        A. COCl2

      B. CC14

      C. CrC13

      D. Cr2O3

 

20. If the reaction began with 5.00 g of Cr2O3  and 12.0 g of CC14  to form CrCl3 and COCl2  (unbalanced) determine the limiting reactant and the amount in excess.

 

      A. Limiting: CC14, 1.05 g Cr2O3 left over              C. Limiting: CC14, 3.70 g Cr2O3 left over

      B. Limiting: Cr2O3, 10.0 g CC14 left over              D. Limiting: Cr2O3, 6.75 g CCl4 left over

 

21. Identify the limiting reagent, and the number of grams left over in excess, respectively, for the following equation, if 1.9 grams each of phosgene and sodium hydroxide are combined.

                   COCl2   +   2NaOH   à   2NaCl + H2O + CO2

 

      A. Limiting: C0C12, 0.588 g NaOH left over     C. Limiting NaOH, 0.520 g COCl2 left over

      B. Limiting: COCI2, 0.37 g NaOH left over       D Limiting NaOH,  0.355 g COC12 left over

 

 

 

Free Response Exercises

 

22. An element ‘E’ is present as “E” with a mass value of 10.01 amu, and as “F” with a mass value of 11.01 amu. The natural abundances of E and F are 19.7800% and 80.2200% respectively. What is the average atomic mass of the element?  What is the element?

 

 

 

 

 

 

 

23. Naturally occurring sulfur consists of four isotopes. 32S (95.00 %), 33S (0.760%), 34S (4.22%), and 36S (0.014%). Using these data, calculate the atomic weight of naturally occurring sulfur. The masses of the isotopes are given in the table below.

Isotope

32S

33S

34S

36S

Atomic mass

(amu)

31.97

32.97

33.97

35.97

 

24. Complete the following table of isotopic information for the element neon (Ne).

Isotope

20Ne

21Ne

22Ne

Mass (amu)

19.99

20.99

21.99

 

 

Abundance

                                                                            ?

0.      25700

?

 

25.Silicon has three stable isotopes in nature as shown in the table below. Fill in the missing information.

 

Isotope

28Si

29Si

32Si

                          Mass (amu)

                               27.98

                                   ?

                               29.97

 

Abundance

                                                                       ?

4.70%

3.09%

 

26. How many moles are in a sample of 300 atoms of nitrogen? How many grams?

 

27. How many atoms of gold does it take to make 1 gram of gold?

 

28. A sample of sulfur has a mass of 5.37 g. How many moles are in the sample?

 

29. How many grams of zinc are in 1.16 x 1022 atoms of zinc?

 

30. How many grams are in 3.68 moles of iron?

 

31. Calculate the molar masses of each of the following:

      a. Cu2SO4       c. C10H16O     e. Ca2Fe(CN)6▪12H20

      b. NH4OH     d. Zr(Se03)2                f. Cr4(P207)3
32. Calculate the molar mass of

      a. Zn(CN)4

      b. Cu(NH3)4•8H20

 

33. What is the mass of 4.28 x 1022 molecules of water?

 

 

34. How many sodium ions are present in each of the following:

 

a.   2 moles of sodium phosphate

b.   5.8 grams of sodium chloride

 

35. How many potassium ions are present in each of the following:

 

a.   3 moles of potassium chloride

b.   6.2 grams of potassium nitrate

c.   a mixture containing 12.6 grams of potassium phosphate and 5.4 grams of potassium chloride’?

 

36. How many moles are there in a sample of barium sulfate (BaSO4) weighing 9.90g?

 

37. How many grams are there in 0.36 moles of cobalt (III) acetate (Co(C2H3O2)3)?

 

38. Bauxite, the principle ore used in the production of aluminum cans, has a molecular formula of A1203•2H20.

 

a.   Determine the molar mass of bauxite.

b.   How many grams of Al are in 0.58 moles of bauxite?

c.   How many atoms of Al are in 0.58 moles of bauxite?

d.   What is the mass in grams of 2.1 X 1024 formula units of bauxite?

 

39. Calculate the mass percent of each element in natural lucite (KAlSi2O6).

 

40. Calculate the mass percent of each of the elements in Nicotine (C10H14N2).

 

41. Determine the empirical and molecular formulas of a compound that has a mass of 31.04 g/mole and contains the following percentages of elements by mass:

 

C 38.66%, H= 16.24%. N~45.10%

 

42. The analysis of a solid rocket fuel (hydrazine) showed that it contained 87.4% nitrogen and 12.6% hydrogen by weight. Mass spectral analysis showed the fuel to have a molar mass of 32.05 grams. What are the empirical and molecular formulas of the fuel’?

 

 

43. A compound is found, by mass spectral analysis, to contain the following percentages of elements by mass:

 

C 49.67%, Cl 48.92%, H 1.39%

 

The molar mass of the compound is 289.9 g/mole. Determine the empirical and molecular formula of the compound.

 

44. Determine the empirical formula of a compound that contains the following percentages of elements by mass:

 

Mo=43.95%, O=7.33% C1=48.72%

 

45. Using the data provided, calculate the empirical formulas for the compounds indicated:

 

a.   an oxide of nitrogen, a sample of which contains 6.35 g of nitrogen and 3.65 g of oxygen

b.   an oxide of copper, one gram of which contains 0.7989 g of copper

c.   an oxide of carbon that contains 42.84% carbon

d.   a compound of potassium, chloride, and oxygen, containing K = 3l.97%, 0 = 39.34%

e.   a compound of hydrogen, carbon and nitrogen containing H 3.70%, C = 44.44%, and N = 51,85%.

 

46. The following reaction was performed:

      Fe203(s) + 2X(s)                  à       2Fe(s) + X203(s)

 

It was found that 79.847 g of Fe2O3 reacted with “X” to form 55.847 g of Fe and 50.982 g of X2O3. Identify element X.

 

 

47. Fill in the blanks to balance the following chemical equations:

      a. ___AgI +        Na2s      à  ___Ag2S + ___NaI

      b. ___(NH4)2Cr2O7               à     Cr203 + ___N2 + ___H20
      c. ___Na3PO4 + ____HC1à  ___NaCl +  ___H3P04
      d. __TiCl4  +  H20               à   Ti02  +  __HC1
      e. ___Ba3N2 + ___H20       à  ___Ba(OH)2 + ___NH3

      f.  __HNO2 à  ___HNO3+         NO+ __H2O

 

 

48. Complete the following reactions (making sure they are balanced):

      a. _____HN03     + ____        à   _____H20  +______ KNO3
      b. _______          + Na3PO4     à    _____Ca3(PO4)2   +  ________NaCl
      c. _____Mg(OH)2  + _______HC1   à   _____ MgCl2        +_____
      d. _______          +  ____ Cl2 à     ______NaCl  +    _______ Br2

 

49. How many grams of water vapor can be generated from the combustion of 18.74 g of ethanol? C2H60(g) + O2(g) à  C02(g) + H20(g) (unbalanced)

 

50. How many grams of sodium hydroxide are required to form 51.63 g of lead hydroxide?

      Pb(N03)2(aq) + NaOH(aq)   à   Pb(OH)2(s) + NaNO3(aq) (unbalanced)

 

51. How many grams of oxygen are necessary to completely react with 22.8 grams of methane, CH4? (Please write the entire reaction).