html5-img
1 / 18

Chapter 7: Moles and Quantities

Chapter 7: Moles and Quantities. A. Moles: Mole – a given quantity (amount) of a substance - the molar mass (gram formula mass or molecular weight) of any substance (changes for each substance) - 22.4 L of any gas - 6.02 x 10 23 particles in any substance.

thurman
Télécharger la présentation

Chapter 7: Moles and Quantities

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Chapter 7: Moles and Quantities A. Moles: • Mole – a given quantity (amount) of a substance - the molar mass (gram formula mass or molecular weight) of any substance (changes for each substance) - 22.4 L of any gas - 6.02 x 1023particles in any substance

  2. B. Molar Mass: • Molar mass – add up masses of all atoms in a compound from the P.T. - round mass (g) to 1 decimal (.1) ex. MgCl2 24.3 g + (35.5 g x 2) = 95.3 g • Hydrate – a compound with water molecules that are within the substance (do not see) ex. CuSO45H2O ( just means to add) 63.5 + 32.1 + (16.0 x 4) + (18.0 x 5) Answer = 249.6 grams

  3. C. Moles  Mass Conversions: • Factor-Label Method: • First, find molar mass of the substance • Start with the given from the problem • Cancel out units on the diagonal • New unit goes on top • Add #’s in • Multiply top, divide bottom to get answer ex. 2 moles of NaCl, convert to grams 2 moles x 58.5 g = 1 mole 117.0 grams

  4. Proportions Method: • Start with given • Use = sign in between • Cross-Multiply, then divide ex. 2 moles of NaCl, convert to grams 2 moles = x 1 mole 58.5 g (2 moles x 58.5 g) / 1 mole Answer = 117.0 grams

  5. ex. Convert 123.8 grams Li2SO3 to moles 123.8 g x 1 mole = 1.3 moles Li2SO3 93.9 g 123.8 g = x 93.9 g 1 mole (123.8 g x 1 mole) / (93.9 g) = 1.3 moles Li2SO3

  6. D. Moles  Liters Conversions: • 1 mole = 22.4 L of any gas at STP • STP – Standard Temperature and Pressure - at 1 atm (atmosphere) of pressure and 0 C • Start with the given • Show work (factor-label or proportions) • The compound does not matter • Do not need to find the molar mass

  7. E. Moles  Particles Conversions: • 1 mole = 6.02 x 1023particles (or molecules) of any substance • 6.02 x 1023 = Avogadro’s number • Start with the given • Show work (factor-label or proportions) • The compound does not matter • Do not need to find the molar mass

  8. F. Multi-Step Mole Conversions: • When “mole” is not in the question as either the given or the find (the question) • Convert the given to moles • Convert moles to the find • Show work (factor-label or proportions)

  9. ex. How many grams are in 2.7 L of NO2? 2.7 L x 1 mole x 46 g = 5.5 g NO2 22.4 L 1 mole 2.7 L = x 22.4 L 46 g x = 5.5 g NO2

  10. G. Percent Composition: • Percent composition – the percent by mass of each element in a compound • Formulas: % comp = grams of element x 100 grams of compound % comp = total mass of element x 100 total mass of compound

  11. ex. 8.2 grams Mg combines with 5.4 grams O to form MgO. What is the percent composition? % comp Mg = (8.2 g / 13.6 g) x 100 = 60.3 % Mg % comp O = (5.4 g / 13.6 g) x 100 = 39.7 % O Total % will always = 100 %

  12. ex. What is the percent composition of K2CrO4? K2CrO4 = 194.2 g % comp K2 = (78.2 g / 194.2 g) x 100 = 40.3 % K % comp Cr = (52.0 g / 194.2 g) x 100 = 26.8 % Cr % comp O4 = (64.0 g / 194.2 g) x 100 = 33.0 % O

  13. H. Empirical vs. Molecular Formulas: • Law of Definite Proportions – for any given compound, the elements always combine in the same proportions or ratio (subscripts) • Empirical formula – the lowest whole-number ratio of elements in a compound (reduced form) • Molecular formula – the “true” formula of a compound (not reduced) ex. H2O2 (hydrogen peroxide) – molecular HO (not a real compound) - empirical

  14. ex. Of the following compounds, which ones are empirical formulas? CH, C2H2, C6H12, CH2O, C2H4O2, C4H8O Answers:CH, CH2O, C4H8O (reduced)

  15. Calculating empirical formulas: • Convert % (comp) to grams (change units) • Convert grams to moles • Divide all mole answers by the smallest mole answer (get you the ratios of atoms) • Write empirical formula based on these mole ratios (should be in the reduced form)

  16. Calculating empirical formulas (cont.): ex. Find the E.F. of: 79.8% C and 20.2% H 79.8 g C x 1 mole = 6.65 moles C = 1 C 12.0 g 6.65 20.2 g H x 1 mole = 20.2 moles H = 3 H 1.0 g 6.65 Answer:CH3

  17. Calculating molecular formulas: • First find empirical formula (if not given) • Find molar mass of empirical formula • Divide the molar mass of molecular formula by the molar mass of empirical formula (given) • Using your answer, multiply all the atoms of the empirical formula to get the new molecular formula • Check molar mass of new found molecular formula

  18. Calculating molecular formulas (cont.): ex. What is the molecular formula with a molar mass of 180 g. if its empirical formula is CH2O? CH2O = 30 g. 180 g / 30 g = 6 (CH2O) Answer:C6H12O6

More Related