The Mole Practice Problems Key

The Mole Practice Problems Key 1. Determine the number of atoms in 3.75 mol Fe. 𝟑. 𝟕𝟓 𝒎𝒐𝒍 𝑭𝒆 𝟔. 𝟎𝟐𝒙𝟏𝟎𝟐𝟑 𝒂𝒕𝒐𝒎𝒔 𝑭𝒆 𝒙 = 𝟐. 𝟐𝟔𝒙𝟏𝟎𝟐𝟒 𝒂𝒕𝒐𝒎𝒔 𝑭𝒆 𝟏 𝒎𝒐𝒍 𝑭𝒆 2. Calculate the number of formula units in 12.5 mol CaCO3. 𝟏𝟐. 𝟓 𝒎𝒐𝒍 𝑪𝒂 𝑪𝑶𝟑 𝟔. 𝟎𝟐𝒙𝟏𝟎𝟐𝟑 𝒇𝒐𝒓𝒎𝒖𝒍𝒂 𝒖𝒏𝒊𝒕𝒔 𝑪𝒂𝑪𝑶𝟑 𝒙 𝟏 𝒎𝒐𝒍 𝑪𝒂 𝑪𝑶𝟑 𝟐𝟒 = 𝟕. 𝟓𝟑 × 𝟏𝟎 𝒇𝒐𝒓𝒎𝒖𝒍𝒂 𝒖𝒏𝒊𝒕𝒔 𝑪𝒂𝑪𝑶𝟑 3. How many moles of CaCl2 contain 1.26 X 1024 formula units CaCl2? 𝟏. 𝟐𝟓 × 𝟏𝟎𝟐𝟒 formula units 𝑪𝒂𝑪𝒍𝟐 × 𝟏mol 𝑪𝒂𝑪𝒍𝟐 = 𝟐. 𝟎𝟗mol 𝑪𝒂𝑪𝒍𝟐 𝟔. 𝟎𝟐 × 𝟏𝟎𝟐𝟑 formula units 𝑪𝒂𝑪𝒍𝟐 4. How many moles of Ag contain 4.59 X 1025 atoms of Ag? 𝟒. 𝟓𝟗 × 𝟏𝟎𝟐𝟓 atoms 𝑨𝒈 𝟏mol 𝑨𝒈 × = 𝟕𝟔. 𝟐 mol 𝑨𝒈 𝟔. 𝟎𝟐 × 𝟏𝟎𝟐𝟑 atoms 𝑨𝒈 5. Determine the mass in grams of 0.0458 moles of sulfur. 𝟎. 𝟎𝟒𝟓𝟖 moles 𝑺 𝟑𝟐. 𝟎𝟕𝒈 𝑺 × = 𝟏. 𝟒𝟕𝒈 𝑺 𝟏mol 𝑺 6. Calculate the mass in grams of 2.56 X 10-3 moles of iron. 𝟐. 𝟓𝟔 × 𝟏𝟎−𝟑 moles 𝑭𝒆 𝟓𝟓. 𝟖𝟓𝒈 𝑭𝒆 × = 𝟎. 𝟏𝟒𝟑𝒈 𝑭𝒆 𝟏mol 𝑭𝒆 7. Determine the mass in grams of 125 mol of neon. 𝟏𝟐𝟓 moles 𝑵𝒆 𝟐𝟎. 𝟏𝟖𝒈 𝑵𝒆 × = 𝟐. 𝟓𝟐 × 𝟏𝟎𝟑 𝒈 𝑵𝒆 𝟏mol 𝑵𝒆 8. How many moles of titanium are contained in 71.4g of Ti? 𝟕𝟏. 𝟒𝒈 𝑻𝒊 𝟏mol 𝑻𝒊 × = 𝟏. 𝟒𝟗mol 𝑻𝒊 𝟒𝟕. 𝟖𝟖𝒈 𝑻𝒊 9. How many moles of lead are equivalent to 9.51 X 103g of lead? 𝟗. 𝟓𝟏 × 𝟏𝟎𝟑 𝒈 𝑷𝒃 𝟏mol 𝑷𝒃 × = 𝟒𝟓. 𝟗mol 𝑷𝒃 𝟐𝟎𝟕. 𝟐𝟎𝒈 𝑷𝒃 10. Determine the number of moles of arsenic in 1.90g As. 𝟏. 𝟗𝟎𝒈 𝑨𝒔 𝟏mol 𝑨𝒔 × = 𝟎. 𝟐𝟓mol 𝑨𝒔 𝟕𝟒. 𝟗𝟐𝒈 𝑨𝒔 11. Determine the number of atoms in 4.56 X 10-2g of sodium. 𝟒. 𝟓𝟔 × 𝟏𝟎−𝟐 𝒈 𝑵𝒂 𝟏mol 𝑵𝒂 𝟔. 𝟎𝟐 × 𝟏𝟎𝟐𝟑 atoms 𝑵𝒂 × × = 𝟏. 𝟏𝟗 × 𝟏𝟎𝟐𝟏 atoms 𝑵𝒂 𝟐𝟐. 𝟗𝟗𝒈 𝑵𝒂 𝟏mol 𝑵𝒂 12. How many atoms of gallium are in 2.85 X 103g of gallium? 𝟐. 𝟖𝟓 × 𝟏𝟎𝟑 𝒈 𝑮𝒂 𝟏 𝒍 𝑮𝒂 𝟔. 𝟎𝟐 × 𝟏𝟎𝟐𝟑 atoms 𝑮𝒂 × × = 𝟐. 𝟒𝟔 × 𝟏𝟎𝟐𝟓 atoms 𝑮𝒂 𝟔𝟗. 𝟕𝟐𝒈 𝑮𝒂 𝟏mol 𝑮𝒂 13. Determine the mass in grams of 5.65 X 1024 atoms Se. 𝟓. 𝟔𝟓 × 𝟏𝟎𝟐𝟒 atoms 𝑺𝒆 × 𝟏mol 𝑺𝒆 𝟕𝟖. 𝟗𝟔𝒈 𝑺𝒆 × = 𝟕. 𝟒𝟏 × 𝟏𝟎𝟐 𝒈 𝑺𝒆 𝟐𝟑 𝟔. 𝟎𝟐 × 𝟏𝟎 atoms 𝑺𝒆 𝟏mol 𝑺𝒆 14. What is the mass in grams of 3.75 X 1021 atoms Li? 𝟑. 𝟕𝟓 × 𝟏𝟎𝟐𝟏 atoms 𝑳𝒊 𝟏mol 𝑳𝒊 𝟔. 𝟗𝟒𝒈 𝑳𝒊 × × = 𝟒. 𝟑𝟐 × 𝟏𝟎−𝟐 𝒈 𝑳𝒊 𝟐𝟑 𝟔. 𝟎𝟐 × 𝟏𝟎 atoms 𝑳𝒊 𝟏mol 𝑳𝒊 15. Determine the molar mass of silver nitrate. 𝑨𝒈 = 𝟏𝟎𝟕. 𝟖𝟕 𝑵 = 𝟏𝟒. 𝟎𝟏 𝑶 = 𝟏𝟔. 𝟎𝟎 × 𝟑 𝑨𝒈(𝑵𝑶𝟑 ) = 𝟏𝟔𝟗. 𝟖𝟖𝒈 16. Calculate the molar mass of acetic acid (CH3COOH). 𝑪 = 𝟏𝟐. 𝟎𝟏 × 𝟐 𝑯 = 𝟏. 𝟎𝟏 × 𝟒 𝑶 = 𝟏𝟔. 𝟎𝟎 × 𝟐 𝑪𝑯𝟑 𝑪𝑶𝑶𝑯 = 𝟔𝟎. 𝟎𝟔𝒈 17. Determine the mass of 8.57 mol of sodium dichromate (Na2Cr2O7). 𝟖. 𝟓𝟕moles 𝑵𝒂𝟐 𝑪𝒓𝟐 𝑶𝟕 𝟐𝟔𝟏. 𝟗𝟖𝒈 𝑵𝒂𝟐 𝑪𝒓𝟐 𝑶𝟕 × = 𝟐. 𝟐𝟓 × 𝟏𝟎𝟑 𝒈 𝑵𝒂𝟐 𝑪𝒓𝟑 𝑶𝟕 𝟏mol 𝑵𝒂𝟐 𝑪𝒓𝟐 𝑶𝟕 18. Calculate the mass of 42. 5 mol of potassium cyanide. 𝟒𝟐. 𝟓moles 𝑲𝑪𝑵 𝟔𝟓. 𝟏𝟐𝒈 𝑲𝑪𝑵 × = 𝟐. 𝟕𝟕 × 𝟏𝟎𝟑 𝒈 𝑲𝑪𝑵 𝟏mol 𝑲𝑪𝑵 19. Determine the number of moles present in 456 g Cu(NO3) 2. 𝟒𝟓𝟔𝒈 𝑪𝒖(𝑵𝑶𝟑 )𝟐 𝟏mol 𝑪𝒖(𝑵𝒖 ) 𝟑 𝟐 × 𝟏𝟖𝟕.𝟓𝟕𝒈 𝑪𝒖(𝑵𝑶 = 𝟐. 𝟒𝟑mol 𝑪𝒖(𝑵𝑶𝟑 )𝟐 ) 𝟑 𝟐 20. Calculate the number of moles in 5.67 g potassium hydroxide. 𝟓. 𝟔𝟕𝒈 𝑲(𝑶𝑯) 𝟏mol 𝑲(𝑶𝑯) × = 𝟎. 𝟏𝟎𝟏mol 𝑲(𝑶𝑯) 𝟓𝟔. 𝟏𝟏𝒈 𝑲(𝑶𝑯) 21. Calculate the number of molecules in 40.0 g of methanol (CH3OH). 𝟒𝟎. 𝟎𝒈 𝑪𝑯𝟑 𝑶𝑯 𝟏mol 𝑪𝑯𝟑 𝑶𝑯 𝟔. 𝟎𝟐 × 𝟏𝟎𝟐𝟑 molecules 𝑪𝑯𝟑 𝑶𝑯 × × 𝟑𝟐. 𝟎𝟓𝒈 𝑪𝑯𝟑 𝑶𝑯 𝟏mol 𝑪𝑯𝟑 𝑶𝑯 𝟐𝟑 = 𝟕. 𝟓𝟏 × 𝟏𝟎 molecules 𝑪𝑯𝟑 𝑶𝑯 22. What mass of sodium hydroxide contains 4.58 x 1023 formula units? 𝟒. 𝟓𝟖 × 𝟏𝟎𝟐𝟑 formula units 𝑵𝒂𝑶𝑯 𝟏mol 𝑵𝒂𝑶𝑯 × 𝟐𝟑 𝟔. 𝟎𝟐 × 𝟏𝟎 formula units 𝑵𝒂𝑶𝑯 𝟒𝟎𝒈𝑵𝒂𝑶𝑯 × = 𝟑𝟎. 𝟒𝒈 𝑵𝒂𝑶𝑯 𝟏mol 𝑵𝒂𝑶𝑯 Calculate the percent by mass of each element in the following compounds. 23. Sucrose (C12H22O11) 𝑪 = 𝟏𝟐. 𝟎𝟏 × 𝟏𝟐 = 𝟏𝟒𝟒. 𝟏𝟐 𝑯 = 𝟏. 𝟎𝟏 × 𝟐𝟐 = 𝟐𝟐. 𝟐𝟐 𝑶 = 𝟏𝟔. 𝟎𝟎 × 𝟏𝟏 = 𝟏𝟕𝟔 Molar Mass = 𝟏𝟒𝟒. 𝟏𝟐 + 𝟐𝟐. 𝟐𝟐 + 𝟏𝟕𝟔 = 𝟑𝟒𝟐. 𝟒𝟑 𝑪 = 𝟏𝟒𝟒. 𝟏𝟐𝟑𝟒𝟐. 𝟒𝟑 × 𝟏𝟎𝟎 = 𝟒𝟐. 𝟏% 𝑯 = 𝟐𝟐. 𝟐𝟐𝟑𝟒𝟐. 𝟒𝟑 × 𝟏𝟎𝟎 = 𝟔. 𝟒𝟗% 𝑶 = 𝟏𝟕𝟔𝟑𝟒𝟐. 𝟒𝟑 × 𝟏𝟎𝟎 = 𝟓𝟏. 𝟒% 24. Magnetite (Fe3O4) 𝑭𝒆 = 𝟓𝟓. 𝟖𝟓 × 𝟑 = 𝟏𝟔𝟕. 𝟓𝟓 𝑶 = 𝟏𝟔. 𝟎𝟎 × 𝟒 = 𝟔𝟒 Molar Mass = 𝟏𝟔𝟕. 𝟓𝟓 + 𝟔𝟒 = 𝟐𝟑𝟏. 𝟓𝟓 𝑭𝒆 = 𝟏𝟔𝟕. 𝟓𝟓𝟐𝟑𝟏. 𝟓𝟓 × 𝟏𝟎𝟎 = 𝟕𝟐. 𝟒% 𝑶 = 𝟔𝟒𝟐𝟑𝟏. 𝟓𝟓 × 𝟏𝟎𝟎 = 𝟐𝟕. 𝟔% 25. Aluminum sulfate (Al2(SO4)3) 𝑨𝒍 = 𝟐𝟔. 𝟗𝟖 × 𝟐 = 𝟓𝟑. 𝟗𝟔 𝑯 = 𝟏. 𝟎𝟏 × 𝟑 = 𝟑. 𝟎𝟑 𝑶 = 𝟏𝟔. 𝟎𝟎 × 𝟏𝟐 = 𝟏𝟗𝟐 Molar Mass = 𝟓𝟑. 𝟗𝟔 + 𝟑. 𝟎𝟑 + 𝟏𝟗𝟐 = 𝟐𝟒𝟖. 𝟗𝟗 𝑪 = 𝟓𝟑. 𝟗𝟔𝟐𝟒𝟖. 𝟗𝟗 × 𝟏𝟎𝟎 = 𝟐𝟏. 𝟕% 𝑯 = 𝟑. 𝟎𝟑𝟐𝟒𝟖. 𝟗𝟗 × 𝟏𝟎𝟎 = 𝟏. 𝟐% 𝑶 = 𝟏𝟗𝟐𝟐𝟒𝟖. 𝟗𝟗 × 𝟏𝟎𝟎 = 𝟕𝟕. 𝟏% 26. Which of the following iron compounds contain the greatest percentage of iron: pyrite (FeS2), hematite (Fe2O3), siderite (FeCO3)? 27. Which of the following compounds has a greater percent by mass of chromium, K2CrO4, or K2Cr2O7? Determine the Empirical formula for the following: 28. Propane is a hydrocarbon composed of 81.82% carbon and 18.18% hydrogen. What is the empirical formula? % to g 81.82% carbon = 81.82 g carbon 18.18% hydrogen = 18.18 g hydrogen Grams to mole 𝟖𝟏. 𝟖𝟐𝒈 𝑪 × 𝟏mol 𝑪 = 𝟔. 𝟖𝟏𝟐mol 𝑪 𝟏𝟐. 𝟎𝟏𝒈 𝑪 𝟏𝟖. 𝟏𝟖𝒈 𝑯 × 𝟏mol 𝑯 = 𝟏𝟖mol 𝑯 𝟏. 𝟎𝟏𝒈 𝑯 Divide by smallest 6.812/ 6.812 = 1 18 / 6.812 = 2.64 Multiply ‘til Whole 𝟏 ×𝟑 = 𝟑 𝟐. 𝟔𝟒 × 𝟑 = 𝟖 C3H8 29. Analysis of a compound composed of iron and oxide yields 174.86 g Fe and 75.14 g O. What is the empirical formula for this compound? % to g Already in grams Grams to mole 𝟏𝟕𝟒. 𝟖𝟔𝒈 𝑭𝒆 × 𝟕𝟓. 𝟏𝟒𝒈 𝑶 × 𝟏mol 𝑭𝒆 = 𝟑. 𝟏𝟑mol 𝑭𝒆 𝟓𝟓. 𝟖𝟓𝒈 𝑭𝒆 𝟏mol 𝑶 = 𝟒. 𝟔𝟗mol 𝑶 𝟑𝟖𝒈 𝑶 Divide by smallest 3.13 / 3.13 = 1 4.69 / 3.13 = 1.5 Multiply ‘til Whole 𝟏 ×𝟐 = 𝟐 𝟏. 𝟓 × 𝟐 = 𝟑 Fe2O3 30. A compound has 67.6% Mercury, 10.8% Sulfur, and 21.6% Oxygen. Determine the Empirical formula for this compound. % to g 67.6% Hg = 67.6 g Hg 10.8% S = 10.8 g S 21.6% O = 21.6 g O Grams to mole 𝟔𝟕. 𝟔𝒈 𝑯𝒈 × 𝟏mol 𝑯𝒈 = 𝟎. 𝟑𝟑mol 𝑯𝒈 𝟖𝟎𝟎. 𝟓𝟗𝒈 𝑯𝒈 𝟏𝟎. 𝟖𝒈 𝑺 × 𝟏mol 𝑺 = 𝟎. 𝟑𝟑mol 𝑺 𝟑𝟐𝒈 𝑺 𝟐𝟏. 𝟔𝒈 𝑶 × 𝟏mol 𝑶 = 𝟏. 𝟑mol 𝑶 𝟑𝟐. 𝟎𝟎𝒈 𝑶 Divide by smallest 0.337 / 0.33 = 1 0.312 / 0.33 = 1 1.3 / 0.33 = 4 Multiply ‘til Whole Already whole numbers HgSO4 31. 1, 6-diaminohexane is used to make nylon. What is the empirical formula of this compound if it is 62.1% carbon, 13.8% hydrogen, and 24.1% nitrogen? % to g 62.1% C = 62.1 g C 13.8% H = 13.8 g H 24.1% N = 24.1 g N Grams to mole 𝟔𝟐. 𝟏𝒈 𝑪 × 𝟏mol 𝑪 = 𝟓. 𝟏𝟕mol 𝑪 𝟏𝟐. 𝟎𝟏𝒈 𝑪 𝟏𝟑. 𝟖𝒈 𝑯 × 𝟏mol 𝑯 = 𝟏𝟑. 𝟔𝟔mol 𝑯 𝟏. 𝟎𝟏𝒈 𝑯 𝟐𝟒. 𝟏𝒈 𝑵 × 𝟏mol 𝑵 = 𝟏. 𝟕𝟐mol 𝑵 𝟏𝟒. 𝟎𝟒𝒈 𝑵 Divide by smallest 5.17 / 1.72 = 3 13.66 / 1.72 = 8 1.72 / 1.72 = 1 Multiply ‘til Whole Already whole numbers C3H8N Determine the Molecular formula for the following: 32. The compound borazine consists of 40.29% boron, 7.51% hydrogen, and 52.20% nitrogen, and its molar mass is 80.50 g/mol. What is the molecular formula? Empirical Formula = BH2N Molar Mass of BH2N =26.84 g Molecular Formula = B3H6N3 33. The composition of silver oxalate is 71.02% silver, 7.91% carbon, and 21.07% oxygen, and its molar mass is 303.8 g/mol. What is the molecular formula? Empirical Formula = AgCO2 Molar Mass of AgCO2 =151.8 g Molecular Formula = Ag2C2O4 or Ag2(CO2)2 34. A compound of phosphorus and sulfur contains 27.87% phosphorous and 72.13% sulfur. The molar mass of the compound is 222.3 g/mol. Calculate its molecular formula. Empirical Formula = P2S5 Molar Mass of P2S5 =222.3 g Molecular Formula = P2S5