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# Lecture 12.2b- Gram-Gram Stoich

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Section 12.2 Lecture (part B) for Honors & Prep Chemistry

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• In this Hubble Space Telescope image, clouds of condensed ammonia are visible covering the surface of Saturn.
• In this Hubble Space Telescope image, clouds of condensed ammonia are visible covering the surface of Saturn.
• With your knowledge of conversion factors and this problem-solving approach, you can solve a variety of stoichiometric problems. Identifying What conversion factor is used to convert moles to representative particles?
• ### Lecture 12.2b- Gram-Gram Stoich

1. 1. <ul><li>A sample of NaCl has a mass of 150g. How many moles does the sample contain? </li></ul><ul><li>What is the mass of 5.3 moles of water? </li></ul>Bellwork- mole  gram conversions mol 18 1 g g mol 1 58.44 = 2.57 moles NaCl = 95.4 grams 5.3 mol x 150g NaCl x
2. 2. <ul><li>STOICHIOMETRY </li></ul><ul><li>You must be able to </li></ul><ul><li>Balance equations </li></ul><ul><li>Convert between moles and grams </li></ul>
3. 3. <ul><ul><ul><li>For Stoichiometry– </li></ul></ul></ul><ul><ul><ul><li>You ALWAYS use moles!! </li></ul></ul></ul><ul><ul><ul><ul><ul><li>If you are not given moles you must convert to moles. </li></ul></ul></ul></ul></ul>
4. 4. <ul><ul><ul><li>For Stoichiometry– </li></ul></ul></ul><ul><ul><ul><li>You ALWAYS use moles!! </li></ul></ul></ul><ul><ul><ul><ul><ul><li>If you are not given moles you must convert to moles. </li></ul></ul></ul></ul></ul><ul><ul><ul><li>Use the mole ratio to convert between compounds. </li></ul></ul></ul>
5. 5. <ul><li>Most stoichiometry problems involve masses. </li></ul>
6. 6. <ul><li>Most stoichiometry problems involve masses. </li></ul><ul><li>Convert grams to moles using the molar mass of the given compound. </li></ul>
7. 7. <ul><li>Most stoichiometry problems involve masses. </li></ul><ul><li>Convert grams to moles using the molar mass of the given compound. </li></ul><ul><li>Convert moles of the given compound to moles of the wanted compound using a mole ratio. </li></ul>
8. 8. <ul><li>Most stoichiometry problems involve masses. </li></ul><ul><li>Convert grams to moles using the molar mass of the given compound. </li></ul><ul><li>Convert moles of the given compound to moles of the wanted compound using a mole ratio. </li></ul><ul><li>Convert moles to grams using the molar mass of the new compound. </li></ul>
9. 9. 12.3 Step 2- Use a mole ratio to convert to moles of another compound. 2.7mol H 2 mol H 2 mol NH 3 3 2 = 1.8 mol NH 3 Step 1- CONVERT TO MOLES!! 5.4g H 2 x ______ = 2.7mol H 2 1 mole 2.0g x
10. 10. Step 3- Convert moles to grams 1.8 mol NH 3 1 mole NH 3 17g = 31g NH 3 Step 1- CONVERT TO MOLES!! 5.4g H 2 x ______ = 2.7mol H 2 1 mole 2.0g Step 2- Use a mole ratio to convert to moles of another compound. 2.7mol H 2 x mol H 2 mol NH 3 3 2 = 1.8 mol NH 3 x
11. 11. `
12. 12. <ul><li>Problem-Solving Approach </li></ul>Given(G)  Wanted(W) Divide to get moles Use mole ratio multiply to get g or L
13. 17. <ul><ul><li>N 2 ( g ) + 3H 2 ( g )  2NH 3 ( g ) </li></ul></ul><ul><ul><li>2. What volume of H 2 is required to react with 3.0 L of N 2 , and what volume of NH 3 is produced at STP? </li></ul></ul><ul><ul><ul><li>volume of H 2 = 9.0 L, volume of NH 3 = 6.0 L </li></ul></ul></ul><ul><ul><ul><li>volume of H 2 = 3.0 L, volume of NH 3 = 3.0 L </li></ul></ul></ul><ul><ul><ul><li>volume of H 2 = 3.0 L, volume of NH 3 = 6.0 L </li></ul></ul></ul><ul><ul><ul><li>volume of H 2 = 1.0 L, volume of NH 3 = 1.5 L </li></ul></ul></ul>
14. 18. <ul><ul><li>3. Automotive airbags inflate when sodium azide, NaN 3 , rapidly decomposes to its component elements via this reaction: </li></ul></ul><ul><ul><li>2NaN 3  2Na + 3N 2 . </li></ul></ul><ul><ul><li>How many grams of sodium azide are required to form 5.00 g of nitrogen gas? </li></ul></ul><ul><ul><ul><li>11.61 g </li></ul></ul></ul><ul><ul><ul><li>17.41 g </li></ul></ul></ul><ul><ul><ul><li>7.74 g </li></ul></ul></ul><ul><ul><ul><li>1.36 g </li></ul></ul></ul>