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Chemistry - moles


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A Brief Demonstration about Moles - A chemistry Concept and A Part of Syllabus for Cambridge International Examination O Levels Checkpoint.

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Chemistry - moles

  1. 1. Chemistry - Moles A Demonstration to describe the concept of moles more briefly.
  2. 2. Part 1: Chemical Quantities
  3. 3. Introduction ● How did you determine the number of M&Ms in the bag without actually counting?
  4. 4. Atoms ● Can you determine the number of atoms of an element even though you can not actually count them? ● Yes… IF there is a conversion factor that allows you to convert between mass and number of atoms.
  5. 5. Moles ● The SI base unit that measures amount of substance ● Avogadro’s Number: 6.02 x 1023 atoms
  6. 6. Moles and Atomic Mass ● The atomic mass of an element in grams contains one mole of atoms (Avogadro’s number of atoms) ● Example: There are 6.02 x 1023 (or 1.0 moles) of atoms in 12.011 g of carbon
  7. 7. Moles as Conversion Factors ● Use moles/grams (or grams/moles) as a conversion factor ● Ex: 16.0 g oxygen ----------------------------- 1 mole oxygen
  8. 8. Example 1 ● How many moles of helium atoms are in 6.8 grams?
  9. 9. Example 2 ● How many grams is equal to 1.51 moles of iron?
  10. 10. Examples 3, 4, and 5 ● 17.6 grams of chlorine is equal to how many moles? ● How many moles of nickel do you have if you have 65.1 g? ● React 1.9 moles of sodium with chlorine gas to get sodium chloride. How many grams of sodium do you need?
  11. 11. Calculating Molar Mass ● Atomic Mass of an element = “molar mass” ● Molar mass of a compound must be calculated
  12. 12. Calculating Molar Mass ● How many oxygens are in a DOZEN water molecules? ● How many hydrogens?
  13. 13. Calculating Molar Mass ● One mole of WATER MOLECULES (H2 O) is one mole of oxygen atoms and two moles of hydrogen atoms ● Calculate the mass of one mole of water molecules
  14. 14. Calculate the molar mass of… ● Boron Trifluoride ● Sodium Iodide ● Sodium Bicarbonate (NaHCO3 ) ● Glucose (C6 H12 O6 ) ● Copper (III) Sulfate
  15. 15. REMEMBER! ● Molar mass is the mass of one mole of an element/compound. ● Molar mass has units of grams/mole. ● Molar mass can be used as a conversion factor to find grams or find moles.
  16. 16. What you should know so far: ●Explain the concept of a “mole” and give a definition ●Explain how one mole of an element is related to atomic mass ●Find the molar mass of an element (using correct units) ●Determine the number of grams/moles of a given element using molar mass ●Calculate the molar mass of a compound ●Determine the number of grams/moles of a given compound using molar mass
  17. 17. Making A Solution ● You want to make a solution by dissolving 4.00 moles of potassium nitrate in water. How many grams of the compound will you need?
  18. 18. Example! ● Calculate the number of moles in a 13.8-g sample of butane lighter fluid. The formula for butane is C4 H10 .
  19. 19. Find the mass of: ●0.702 mol Be. ●2.40 mol N2 . ●0.160 mol H2 O2 . ●5.08 mol NaNO3 . Find the number of moles. ●187 g Al ●0.264 g Li2 HPO4 ●333 g SnF2
  20. 20. ● How many grams are in 5.66 mol of CaCO3 ?
  21. 21. ● How many moles are in 508 grams of ethanol, CH3 CH2 OH?
  22. 22. Part 2: Moles of a Gas
  23. 23. Gases ● Solids/liquids are packed tightly together and more space is needed if atoms/molecules are larger ● Atoms/molecules in gases are far apart, so larger atoms/molecules do not need more space
  24. 24. Mole-Volume Relationship ● Avogadro’s Hypothesis – equal volumes of gases contain equal numbers of particles ● 1 mole of any gas takes up the same volume as long as…
  25. 25. STP ● …as long as the gases are at the same pressures and temperatures ● STP, or “standard temperature and pressure” means 0o C and 1 atmosphere, which is air pressure at sea level
  26. 26. Calculating Moles of a Gas ● At STP, a mole of any gas takes up 22.4 liters. ● Use 22.4 L /mol as a conversion factor!
  27. 27. Example 1 ● How many liters will a 0.19-mole sample of oxygen gas take up?
  28. 28. Example 2 ● A blimp has a volume of 95 kL (95,000 L). If it is filled with helium at STP, how many moles of the gas are contained within the blimp?
  29. 29. Examples 3 and 4 ● Find the number of moles in a sample of chlorine gas stored in a 14.2-liter tank at STP. ● What is the volume of 0.18 moles of xenon at STP?
  30. 30. During Last Week’s Episode… ● Look up molar mass of elements / calculate molar mass of compounds ● Convert moles-grams using molar mass as the conversion factor (elements and compounds) ● Convert moles-liters of a gas using molar volume (22.4 L/mol)
  31. 31. MOLES Mass (g) Volume (L) # Atoms Conversion Factor: molar mass Conversion Factor: molar volume (22.4 L / 1 mol) Conversion Factor: Avogadro’s number 6.02 x 1023 atoms/mol
  32. 32. Challenge Problem ● Calculate the mass of 16.4 L of chlorine gas at STP.
  33. 33. Part 3: Molarity
  34. 34. Molarity Molarity is a measure of how concentrated a solution is Amount of solute per volume of solution High concentration / high molarity
  35. 35. Molarity Measured in units of moles/liter mol/L = “M” A 2.5 M solution has 2.5 moles of salt in one liter of water
  36. 36. Molarity Problems To make one liter of a 2.5 molar solution of sodium chloride, how many grams of sodium chloride do you need?
  37. 37. Molarity Problems SET MOLARITY PROBLEMS UP AS A PROPORTION! ●How many moles of silver nitrate (AgNO3 ) are in 0.4 L of a 6.0 M solution? ●How many grams of silver nitrate is that?
  38. 38. Molarity Problem #3 How many grams of lead(IV) chloride must be dissolved in 50 mL of water to make a 0.1 M solution? Remember: 0.1 M = 0.1 mol/L
  39. 39. Molarity Problem #4 ●If you dissolve 56 g of sugar (sucrose, C12 H22 O11 ) into a liter of water, what is the molarity of the solution you created?
  40. 40. Part 3: Percent Composition Section 10.3, page 305
  41. 41. ● Methane, CH4 , is made of solely hydrogen and carbon. What percent of the compound is hydrogen? What percent is carbon?
  42. 42. Percent Composition ● Remember that some atoms are larger, by mass, than others ● Mass of each atom must be taken into account when calculating percent composition
  43. 43. Percent Composition ● Percent composition = % (by mass) of each atom in a compound mass of element % composition = --------------------------- x 100% mass of compound
  44. 44. Example 1 ● 15.1 grams of oxygen combine with 1.9 g of hydrogen to make water. Find the percent composition of each element.
  45. 45. Example 2 ● A sample of glucose is synthesized from 58.00 g carbon, 9.73 g hydrogen, and 77.27 g oxygen. Find the percent composition for each element.
  46. 46. Percent Composition and Chemical Formulas ● Allows you to find the % composition of an element in a compound without knowing the mass of that element molar mass of element % composition = --------------------------------------- x 100% molar mass of compound
  47. 47. Example 1 ● What percentage of a sample of table salt, sodium chloride, is sodium?
  48. 48. Example 2 ● Determine the percent composition of iron (III) oxide.
  49. 49. Example 3 ● Hypochlorous acid is one of the active sanitizers in pool-cleaning products. Its formula is HClO. What percent of the compound is oxygen?
  50. 50. Using Percent Composition to Calculate Mass ● To calculate mass of one element in a specific mass of a compound, multiply the mass of the compound by the percent composition of that element.
  51. 51. Using Percent Composition to Calculate Mass ● Example: ● Carbon is 27.3% of CO2 . Of 45.1 g of CO2 , what mass is carbon? 27.3% x 45.1 g = 12.3 g
  52. 52. Example 1 ● Find the number of grams of sodium in 10.1 g of sodium sulfate. ● HINT! First write the formula for sodium sulfate, then find the % sodium.
  53. 53. Thank You A Presentation by Irfad Imtiaz
  54. 54. Stay Tuned