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Mass Relationships in Chemical Reactions

Mass Relationships in Chemical Reactions. Chapter 3. Empirical Formula of a Hydrate. Hydrated copper (II) sulfate has the formula CuSO 4 · x H 2 O. To find x , 1.023 g of the blue solid is heated in a crucible until its mass no longer decreases.

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Mass Relationships in Chemical Reactions

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  1. Mass Relationships in Chemical Reactions Chapter 3

  2. Empirical Formula of a Hydrate Hydrated copper (II) sulfate has the formula CuSO4· x H2O. To find x, 1.023 g of the blue solid is heated in a crucible until its mass no longer decreases. The mass of the anhydrous, white CuSO4 is 0.654 g. How many moles of water (x) are there per mole of CuSO4?

  3. Mass Changes in Chemical Reactions a.k.a. “Stoichiometry”

  4. 2CH3OH + 3O2 2CO2 + 4H2O grams CH3OH moles CH3OH moles H2O grams H2O 4 mol H2O 18.0 g H2O 1 mol CH3OH x = x x 2 mol CH3OH 32.0 g CH3OH 1 mol H2O Methanol burns in air according to the equation If 209 g of methanol are used up in the combustion, what mass of water is produced? molar mass CH3OH molar mass H2O coefficients chemical equation 209 g CH3OH 235 g H2O

  5. Given the following balanced equation, 2Mg + O2→ 2MgO (a) how many grams of oxygen are required to completely react with 0.145 g of magnesium? (b) How many grams of magnesium oxide are formed?

  6. Limiting Reagent • Reactant that is present in the smaller or smallest • required stoichiometric ratio 2 H2 (g) + O2 (g) → 2 H2O (v) Fig 3.15

  7. 2 H2 (g) + O2 (g) → 2 H2O (v) Fig 3.15 • i.e., in this case O2 is in excess • and H2 is the limiting reagent (LR) • The amount of product depends on LR alone!!

  8. How do we determine the limiting reagent? Calculate the theoretical yield twice: Assume first reagent is LR and calculate Assume second reagent is LR and calculate The smaller result gives LR and yield

  9. Sample exercise 3.19 p 104 How many grams of water will be formed from 150 g H2 and 1500 g O2 in a fuel cell? 2 H2 (g) + O2 (g) → 2 H2O (v) Ans: 1400 g H2O This is the theoretical yield

  10. Actual Yield Theoretical Yield Percent Yield = x 100% • Theoretical yield - the maximum amount of product that can be made • In other words it’s the amount of product possible as calculated through the stoichiometry problem. • This is different from the actual yield, which is the amount one actually produces and measures.

  11. Sample exercise 3.19 p 104 How many grams of water will be formed from 150 g H2 and 1500 g O2 in a fuel cell? 2 H2 (g) + O2 (g) → 2 H2O (v) Ans: 1400 g H2O This is the theoretical yield Assume, say, 1250 g H2O are formed. Then percent yield =

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