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Formulas, Equations, and Moles

Formulas, Equations, and Moles. Chapter 3. Molar Mass. The sum of the atomic masses for all the atoms represented in the chemical formula of a compound. AKA formula mass, molecular mass, molecular weight. Mole (mol). Number of particles in atomic mass in grams of an element.

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Formulas, Equations, and Moles

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  1. Formulas, Equations, and Moles Chapter 3

  2. Molar Mass • The sum of the atomic masses for all the atoms represented in the chemical formula of a compound. • AKA formula mass, molecular mass, molecular weight

  3. Mole (mol) • Number of particles in atomic mass in grams of an element. • Number of molecules/formula units in the molar mass in grams of a compound • 6.02 x 1023 particles.

  4. Fill in the table for 1 mol of butyl mercaptan (skunk odor)

  5. How many water molecules are in one drop of water? (One drop of water is 1/20 of a mL, and the density of water is 1.0 g/mL.) • How many hydrogen atoms are in a drop of water?

  6. Percent Composition • Nitrogen fixation in the root nodules of peas and other legumes occurs with a reaction involving a molybdenum containing enzyme named nitrogenase. This enzyme contains two Mo atoms per molecule and is 0.0872% Mo by mass. What is the molar mass of the enzyme?

  7. Empirical Formulas • Simplest formula for a compound. • Can be determined from percent composition data and combustion analysis.

  8. An analysis of nicotine, a poisonous compound found in tobacco leaves, shows that it is 74.0% C, 8.65% H, and 17.35% N. Its molar mass is 162 g/mol. Determine the empirical and molecular formulas for nicotine.

  9. A compound of Ca, C, N, and S was subjected to quantitative analysis and formula mass determination, and the following data were obtained. A 0.250 g sample was mixed with NaCO3 to convert all of the Ca to 0.160 g of CaCO3. A 0.115 g sample of the compound was carried through a series of reactions until all of its S was changed to 0.344g of BaSO4. A 0.712 g sample was processed to liberate all of its N as NH3, and 0.155 g NH3 was obtained. The formula mass was found to be 156. Determine the empirical and molecular formulas of this compound.

  10. Mass percent • (mass part/mass whole) x 100(%) • An aqueous solution of acetic acid is 20 percent by weight Acetic acid has a density of 1.0269 g/mL. How many moles of acetic acid are contained in 35 mL of this solution?

  11. Molarity (M) • Mole solute/ Liter solution • 128 mL of 0.306 M Na2SO4 is mixed with 220 mL of 0.827 M NaCl. Inventory the resulting molarities of the ions.

  12. Dilution problem • For molarity -- M1V1 = M2V2 • A chemist wants to prepare 0.25 M HCl. Commercial HCl is 12.4M. How many mL of the concentrated acid does the chemist require to make up 1.50 L of the dilute acid?

  13. Stoichiometry Disulfur dichloride S2Cl2, is used to vulcanize rubber. It can be made by treating molten sulfur with gaseous chlorine S8(l) + 4 Cl2(g)  4 S2Cl2(g) Calculate the mass of S2Cl2 that can be produced by reacting 15.0 g of S8 with excess chlorine gas.

  14. Limiting Reagent Stoichiometry Some of the acid in acid rain is produced by the following reaction: 3NO2(g) + H2O(l)  2HNO3(aq) + NO(g) If a falling raindrop weighing 0.050 g comes into contact with 1.0 mg of NO2(g), how much HNO3 can be produced?

  15. One of the steps in the commercial process for converting ammonia to nitric acid involves the conversion of NH3 to NO: • 4 NH3(g) + 5 O2(g)  4 NO(g) + 6 H2O(g) • How many grams of NO form when 1.50 g of NH3 reacts with 1.85 g of O2? • Which reactant is the limiting reactant and which is the excess reactant? • How much of the excess reactant remains after the limiting reactant is completely consumed?

  16. The potassium salt of benzoic acid, potassium benzoate (KC7H5O2) can be made by the action of potassium permanganate on toluene (C7H8) as follows C7H8 + 2KMNO4 KC7H5O2 + 2MnO2 + KOH + H2O If the yield of potassium benzoate cannot realistically be expected to be more than 71%, what is the minimum number of grams of toluene needed to achieve this yield while producing 11.5 g of potassium benzoate?

  17. Solution Stoichiometry • How many milliliters of 0.750 M Pb(NO3)2 solution are required to react completely with 1.00 L of 2.25 M NaCl solution? (Double displacement reaction)

  18. 581 mL of 0.342 M Barium nitrate [Ba(NO3)2] are mixed with 264 mL of 0.631 M potassium sulfate (K2SO4). Write the molecular, ionic, and net ionic reactions for this reaction, calculate the mass of any precipitate produced and inventory the ions in solution after precipitation.

  19. A noncarbonated soft drink contains an unknown amount of citric acid, H3C6H5O7. If 100.0 mL of the soft drink requires 33.51 mL of 0.01024 M NaOH to neutralize the citric acid completely, what is the concentration of citric acid in the soft drink in moles/liter (M)? In equivalents/liter (N)?

  20. A 0.2857 gram sample of sodium phosphate is titrated by 48.22 mL of a sulfuric acid solution. What is the concentration of the sulfuric acid solution? • What is the pH of the sulfuric acid solution? The pOH?

  21. Suppose you are given a 4.554 g sample that is a mixture of oxalic acid, H2C2O4, and another solid that does not react with sodium hydroxide. If 29.58 mL of 0.5501 M NaOH is required to titrate the oxalic acid in the 4.554 g sample, what is the weight percent of oxalic acid in the mixture?

  22. A vitamin C tablet was analyzed to determine whether it did in fact contain, as the manufacturer claimed, 1.00 g of the vitamin. A tablet was dissolved in water to form a 100.00 mL solution, and a 10.00 mL sample was titrated with iodine (as KI3, potassium triiodide). It required 10.10 mL of 0.0521 M I3-1 to reach the stoichiometric point in the titration. Given that vitamin C, C6H8O6, is oxidized todehydroascorbic acid, C6H6O6 and triiodide, I3-1, is oxidized to iodide, I-1, write a balanced equation for the reaction and determine whether the manufacturer’s claim is correct? (MW vitamin C = 176 g/mol)

  23. A 35.49 mL sample of 0.2430 M H2SO4 is mixed with 65.33 mL of a 0.4199 M sample of KOH. Determine the concentration of all ions in solution, the pH, and pOH.

  24. Some compounds can be decomposed quantitatively with water or acid to give known compounds. Suppose you have a 0.643 g sample of a compound known to be composed of C, H, Al, and Cl. Furthermore, you know that it is composed of some number of CH3 groups and chlorine atoms per aluminum atom. The formula could be written as (CH3)xAlCly. To find x and y you decompose the sample with acid in water. The CH3 portion is evolved as methane gas, CH4, and the chloride ions remain in the water. The chloride ions are precipitated as AgCl by adding AgNO3 to the solution. The data collected in the experiment are given here. What are the values of x and y?

  25. (CH3) xAlCly x CH4(g) + Al3+(aq) + y Cl-(aq) • 0.643g 0.222g  • AgNO3 •  • AgCl(s) • 0.996g

  26. The cancer chemotherapy agent, cisplatin, is made by the following reaction: • (NH4)2PtCl4(s) + 2 NH3(aq)  2 NH4Cl(aq) + Pt(NH3)2Cl2(s) • If 15.5 g of (NH4)2PtCl4 is combined with 225mL of 0.75 M NH3 to make cisplatin, • a. Which reactant is in excess and which is the limiting reactant? • b. How many grams of cisplatin can be formed? • c. After all of the limiting reactant has been consumed and the maximum quantity of cisplatin has been formed, how much of the other reactant remain?

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