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Stoichiometry Chapter 9

Stoichiometry Chapter 9 . Step 1. Balance equations and calculate Formula Mass (FM) for each reactant and product. Example: Tin (II) fluoride, SnF 2 , is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride, HF, according to the following equation.

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Stoichiometry Chapter 9

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  1. Stoichiometry Chapter 9

  2. Step 1 • Balance equations and calculate Formula Mass (FM) for each reactant and product. • Example: Tin (II) fluoride, SnF2, is used in some toothpastes. It is made by the reaction of tin with hydrogen fluoride, HF, according to the following equation. Sn (s) + HF(g) SnF2 (s) + H2 (g) How many grams of SnF2 are produced from the reaction of 30.00g of HF with Sn?

  3. Step 1 • Balance the equation • Sn (s) + HF(g) SnF2 (s) + H2 (g) • Sn (s) + 2HF(g) SnF2 (s) + H2 (g) • Calculate Formula Mass for all reactants and products. • Sn= 119 g/molHF= 1+ 19= 20 g/molSnF2= 119 + (2x19) = 157 g/mol H2= 2x1= 2 g/mol

  4. Step 2 • In the example problem we were given mass. • How many grams of SnF2 are produced from the reaction of 30 g of HF with Sn? • We must turn the grams of HF into moles of HF. • Example: • 30gHF 1molHF 20gHF

  5. Step 3 • Determine the ratio of moles from the balanced equation. Sn (s) + 2HF(g) SnF2 (s) + H2 (g) • The ratio is 1mol SnF2 : 2 molHF 30gHF 1molHF 1molSnF2 20gHF 2molHF

  6. Step 3 • BEWARE: • If 2 or more givens are listed, you must determine the limiting reagent: this is the reactant that you have the least amount of moles. • ALWAYSuse the limiting reagent to calculate the problem. If you do not, your answer will ALWAYSbe WRONG.

  7. Step 4 • After calculating the mole ratios, proceed to calculate the mass for the unknown. If question only asks for moles of unknown, you are finished. • Example: • How many grams of SnF2 are produced from the reaction of 30 g of HF with Sn? 30gHF 1molHF 1molSnF2157g SnF2= 117.75g SnF2 20gHF 2molHF 1molSnF2

  8. How To Calculate Percent Yield • You would follow all of the steps for solving stoichiometry . • Using the example from above, let say that the problem read: • When 30.00 grams of HF reacts with an excess of Sn, the actual yield of SnF2 is 100.5 g. What is the percent yield?

  9. How To Calculate Percent Yield • You would have followed all of the steps to calculate that the theoretical yield of SnF2 was 117.75g. • Percent yield = actual yield x 100 theoreticalyield Percent yield= 100.5 g x 100 = 85.3% 117.75g

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