top of page
• StudentGuiders

# CHEM 101-Introductory Chemistry I-EXAM 2

1. The percent composition of aluminum hydroxide is

Al __________34.59_________%

O __________61.533________%

H __________3.877_______%

2. How many grams of water will contain a total number of atoms equal

a. 18.02 grams

3. The number of moles in 0.0355 kilograms of Cl2 is the same as the number of moles in

c. 30.0 grams of HC2H3O2

4. What is the molecular formula of a compound which has an empirical formula of CH2 and a molar mass of 126.2?

n=126.2/14=9.01

C9H18

Chemistry 101 Spring 2020

5. A compound contains 29.9% Carbon, 57.8% chlorine and 13.0% oxygen. The molar mass is 246.0. What are the molecular formula and the empirical formula?

Let the compound be of 100 g

moles of carbon = 29.2 / 12 = 2.43 mol

moles of oxygen = 13.0 / 16 = 0.81 moles

moles of chlorine = 57.8 / 35.5 = 1.63 moles

C : Cl : O = 3 : 2: 1

So C3Cl2O

mass = (12 x 3) + (2 x 35.5) + (1 x 16) = 123 g

246/ 123 = 2

So C6Cl4O2

6. What is the molar mass of ammonium phosphate?

N:14.0067g/mol*3=42.0201

H:1.00784g/mol*12=12.09408

P:30.9737g/mol

O:15.9994g/mol*4=63.9976

N+H+P+O=149.086741g/mol

7. 2.7 x 1024 molecules of CH4

a. weigh 72 grams

8. Calculate the mass percent of each element in the compound aluminum dichromate.

Al:2*26.9815=53.963 7.69%

Cr:6*51.9961=311.9766 44.45%

O:21*15.9994=335.9874 47.87%

9. Barium sulfate is a compound used to assist in diagnosing medical problems through x-ray analysis and is 58.8% barium. What mass of barium is present in a 620 mg tablet of barium sulfate?

c. 360 mg

10. Which one of the following compounds contains the smallest percent oxygen by mass?

d. SO2

11. What mass of dinitrogen monoxide, N2O, contains the same number of molecules as 3.00 g of trichlorofluoromethane, CCl3F?

b. 0.961 g

12. Which of the following statements is false concerning the formula of a compound?

b. The molecular formula is the true ratio of atoms in a compound.

13. How many nitrogen atoms are present in 0.150 mol of zinc nitrate?

b. 1.81 x 1023 atoms

14. Complete the following table.

GAS Number of Number of Mass Moles

Molecules Atoms

N2 5.54 x 1023 1.108*10^24 25.8 0.921

NO2 9.23*10^22 2.77 x 1023 7.05 0.152

NO 5.54*10^25 1.108*10^26 2.76*10^3 2.76 kg

N2O4 6.32*10^22 3.792*10^23 9.66 0.105

CHAPTER 7

15. When Na2CrO4(aq) and AgNO3(aq) are mixed, a red colored precipitate forms which is

b. Ag2CrO4.

16. Which of the following changes represents a physical change, rather than evidence of a chemical reaction?

a. When water and a yellow solution of antifreeze are mixed, the resulting solution is a lighter shade of yellow than the original antifreeze solution.

17. Predict the type of reaction that occurs between each pair of substances, (precipitation, acid-base, gas evolution, or combustion)

and write a balanced chemical equation for each. If no reaction occurs write NO REACTION. This is worth 10 points – 2 points for each.

A. Aqueous potassium hydroxide and aqueous acetic acid.

KOH(aq) + CH3COOH(aq) ------> CH3COOK(aq) + H2O(l)

B. Aqueous hydrochloric acid and sodium hydrogen carbonate.

HCl(aq) + NaHCO3(s) ------> NaCl(aq) + H2O(l) + CO2(g)

C. Aqueous ammonium iodide and aqueous lead(II) nitrate.

2NH4I(aq) + Pb(NO3)2(aq) -----> PbI2(s) + 2NH4NO3(aq)

D. Aqueous sodium chloride and aqueous ammonium acetate.

NaCl(aq) + CH3COONH4(aq) ----------> No reaction

E. Liquid octane (C8H18) and gaseous oxygen

2C8H18(l) + 25O2(g) --------> 16CO2(g) + 18H2O(g)

Write balanced chemical equations for the following word problems QUESTIONS 18 - 23.

18. tin(II) chlorate  tin(II) chloride + oxygen

Sn(ClO3)2 ------ SnCl2+3O2

19. tetraphosphorus decoxide + water  phosphoric acid

P4O10+6H2O ------ 4H3PO4

20. Iron + chlorine  iron(III) chloride

2Fe+3Cl2---------2FeCl3

21. bismuth(III) sulfide + oxygen  bismuth(III) oxide + sulfur dioxide

2Bi2S3+9O2------2Bi2O3+6SO2

22. nitrogen + oxygen  dinitrogen pentoxide

2N2+5O2------20CO2+15H2O

23. Burn decine, C10H15

4C10H15+45O2-----40CO2+30H2O

CHAPTER 8

24. If the percent yield for the reaction

2 CO + O2 → 2 CO2

was 65.8% what mass of product, in grams, could be produced from a reactant mixture containing 35.0 grams of each reactant?

a. 36.2 grams

The next question set (25 - 27) pertains to the following equation (EQUATION is NOT BALANCED):

Na2S2O3 + KMnO4 + H2O  Na2SO4 + K2SO4 + MnO2 + KOH

25. The moles of Na2SO4 obtainable from the reaction of 3.0 moles of Na2S2O3 with 3.0 moles of KMnO4 and 3.0 moles of water is

c. 1.1 moles

26. If the actual yield of Na2SO4 for the reaction described in question 25 was 113 grams what is the percent yield?

1.1*142=159.8g

(113/159.8)*100=70.7%

27. The reaction of 158 grams of KMnO4 will give

a. 0.250 moles of KOH

28. How many grams of sodium cyanide can be produced from 174 grams of calcium cyanide? The reaction that occurs is calcium cyanide reacts

with sodium chloride to form sodium cyanide and calcium chloride.

Calcium cyanide + sodium chloride --> Calcium chloride + sodium cyanide

a. 185

For questions 29 – 31 use the reaction BURN ETHYLENE (C2H4):

29. How many grams of carbon dioxide would be formed if you burned 18 moles of ethylene?

189*2=36mol CO2

30. How many grams of oxygen are required for the complete reaction of 45.0 grams of ethylene?

(45/28.0532)3*31.9986=154g O2

31. If 14.0 grams of ethylene is reacted and the yield of water is 7.84 grams what is the percent yield of water in the reaction?

(14/28.0532)*2*18.01532=17.98g H2O

32. When 75.0 grams of ammonia, 90.0 grams of carbon dioxide and 61.0 grams of water are reacted to form ammonium carbonate, what is the limiting reactant and how many grams of product will be formed?

Moles of NH3 = 75.0/17.03 = 4.404 mol

Moles of H2O = 61.0/18.02 = 3.385 mol

Moles of CO2 = 90.0/44.01 = 2.045 mol

NH3 : H2O : CO2 = 4.404 : 3.385 : 2.045 = 2.154 : 1.655 : 1

Since NH3 and H2O are in excess, CO2 is limiting reactant

Moles of (NH4)2CO3 = moles of CO2 = 2.045 mol

Mass of (NH4)2CO3 = 2.045 x 96.09 = 196.5g

33. If 100 grams of potassium chlorate and 200 grams of hydrochloric acid are allowed to react according to the equation

2 KClO3 + 4 HCl → 2 KCl + 2 ClO2 + Cl2 + 2 H2O

what is the combined total number of moles of chlorine-containing products produced?

2 KClO3 + 4 HCl ---> 2 KCl + 2 ClO2 + Cl2 + 2H2O

Theoretical moles of KClO3 : HCl = 2 : 4 = 0.5 : 1

Moles of KClO3 = 100/122.55 = 0.8160 mol

Moles of HCl = 200/36.46 = 8.228 mol

Experimental moles of KClO3 : HCl = 0.8160 : 8.228 = 0.09917 : 1

Since HCl is in excess, KClO3 is the limiting reagent

Moles of chlorine containing products = 2.5 x 0.8160 = 2.04 mol

34. A mixture of composition 70.0% methane (CH4) and 30% ethane (C2H6) by mass is burned in oxygen to produce carbon dioxide and water. The reactions that occur are

CH4 + 2 O2  CO2 + 2 H2O

2 C2H6 + 7 O2  4 CO2 + 6 H2O

How many grams of oxygen are needed to react completely with 50.0 grams of the hydrocarbon mixture?

c. 196 grams

CHAPTER 11

35. A sample of nitrogen gas occupies a volume of 12.7 mL when measured at 27.0oC and 732 torr. What is the volume of the gas if the pressure is changed to 760. torr and temperature remains at 27.0oC?

c. 12.2 mL

36. Calcium carbonate reacts with hydrochloric acid to make calcium chloride and water and carbon dioxide. How many mL of carbon dioxide at 18oC and 715 mm Hg can be generated from 87.0 grams of calcium carbonate?

e. 2.21 x 104 mL

37. How many moles of Cl2 gas occupy 10.0L at -10 oC and 4.50 atm pressure?

n=(4.5*102)/(0.0821*263.15)

= 20 mole

38. How many liters of carbon dioxide at STP are produced when you burn 112.2 grams of octene, C8H16?

n=112.2/(112.24)=1 mol

v=(22.4/1)*8=179.2 L

179.2L of carbon dioxide gas is obtained at STP during combustion of 112.2g of C8H16

39. If we burn 20.0 L of 1-butene (C4H8) to completion, what is the percent yield if 65 L of carbon dioxide were recovered?

(20*4*22.4)/(22.4=80L CO2

(65/80)*100=81.25%

40. A chemical reaction produces 1.77 moles of oxygen gas at 27oC and 0.933 atm. What volume in liters would this sample occupy?

c. 46.7 L

41. How many liters of excess reactant would be left when 3.00 L of nitrogen monoxide is mixed with 2.00 L of oxygen and allowed to react at 695 torr and 27oC to produce nitrogen dioxide.

b. 0.50 L

42. Sodium chloride reacts with sulfuric acid to make gaseous hydrogen chloride and solid sodium sulfate. What volume of gas in liters at 25oC and 732 torr is expected from 5.00 g of sulfuric acid and 10.0 grams of sodium chloride?

nacl:10*(1/58)=0.171 mol NaCl

H2SO4=5*(1/98.08)=0.051 mol H2SO4

nNaCl:nH2SO4=2:1

moles actual present nNaCl:nH2SO4= 3.4:1

0.051*(2/1)=0.102 mol HCl

V=(0.102*0.0821*298)/(0.96)

= 2.6L

43. A 5.00 L sample of air is collected at 500.oF and 5.00 atm. What is the volume at STP?

V1=(25/533)*273=12.8

44. A 327 mL volume of an unknown gas at 24oC and 739 mm Hg had a mass of 339 mg. Calculate the molar mass of the gas.

b. 26.0 amu

45. Calculate the number of moles of a gas that occupies a volume of

15.9 L at -23oC and 0.52 atm.

b. 0.403 mol

46. What is the value of the gas constant, R, in units of ?

d. 6.236 × 104

47. How many grams of XeF6 are required to react with 0.579 L of hydrogen gas at 2.46 atm and 45°C in the reaction shown below?

XeF6(s) + 3 H2(g) → Xe (g) + 6 HF(g)

B) 4.46 g

CHAPTER 9

48. The element 1s22s22p63s23p64s23d104p65s2 is

c. an alkaline earth metal

49. Identify an ion that is isoelectronic (same electronic structure) with krypton and the write the electronic configuration for that ion.

Sr2+ ---- 1S2 2S2 2P6 3S2 3P6 3d10 4S2 4P6

50. Which atom in each group (I and II) has the smallest atomic radius?

(I) Sr, Zr, I (II) N, P, As

c. I; N

51. Which two ions have the same electron configuration in the ground state?

c. Se2+ and I-

52. What is the ground-state valence-shell electron configuration of the group of elements indicated by the shaded portion of the periodic table?

c. ns2(n-1)d2

CHAPTER 10

53. The electron dot symbol of which of the following elements would have a single dot on each of the four sides of the element's symbol

c. tin

54. In general, at room temperature

b. ionic compounds are all solids, but covalent compounds may be solids, liquids, or gases.

<