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Science 20

Science 20. Unit A: Chemistry Topic: Calculating Concentrations. Do Now. Pg. 42 #29. The Plan. Parts per million Figuring out molar mass Moles per litre I can compare, explain and calculate concentration in the following ways: Percent volume (% V/V) Parts per million (ppm)

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Science 20

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  1. Science 20 Unit A: Chemistry Topic: Calculating Concentrations

  2. Do Now • Pg. 42 #29

  3. The Plan • Parts per million • Figuring out molar mass • Moles per litre I can compare, explain and calculate concentration in the following ways: • Percent volume (% V/V) • Parts per million (ppm) • Molar concentration (mol/L)

  4. Parts Per Million • This refers to the number of grams of solute in 1 000 000 g, or one million grams of solution. • It is calculated by taking the mass of the solute and dividing it by the mass of solution and then multiplying by 10^6 g. • ppm = m solute x 106 ppm m solution Note: this method is used when we are dealing with very small percentages. Remember that 1 mL of water has a mass of 1 g

  5. Parts Per Million E.g., #1 A 500g sample of drinking water contains 0.00150g of boron. The maximum acceptable concentration of boron in drinking water is 5.00 ppm. Does the water sample contain an acceptable amount of boron?

  6. Parts Per Million • Mass of solution = 500g • Mass of solute = 0.00150g • ppm = m solutex 106 ppm m solution = 0.00150 gx 106 ppm 500g = 3.00 ppm

  7. Skunks, Sea Monsters & Parts Per Million • https://www.youtube.com/watch?v=e2txxfmVaiQ

  8. Parts Per Million E.g., #2 A 200 g sample from a bottle of water contains 5.4 x 10-3 g of mercury. • Calculate the concentration of mercury in the sample in parts per million. • Use the information in the table“Allowed Toxic Levels in Drinking Water” (pg. 42) to determine if this water is safe to drink.

  9. Parts Per Million • m solute = 5.4 x 10-3 g m solution = 200 g ppm = ? ppm = m solutex 106 ppm m solution = 5.4 x 10-3 g x 106 ppm 200g = 27 ppm

  10. Parts Per Million b) The acceptable concentration of mercury is 0.001 ppm. The mercury concentration in this water is well above the maximum acceptable limit; therefore, it is NOT safe to drink.

  11. Parts Per Million E.g., #3 Carbon monoxide, CO (g), is a deadly gas that takes the place of oxygen molecules and binds to hemoglobin in blood. If you are smoking, the concentration of carbon monoxide that reaches your lungs is approximately 200 ppm. Determine the mass of CO (g) that would be present in a sample of air having a mass of 9.6 g (approximately one breath). Express your answer in scientific notation.

  12. Parts Per Million • ppm = 200 ppm • m solution = 9.6 g • m solute = ? • m solute = ppmx m solution 106 ppm = 200 ppm x 9.6 g 106 ppm = 0.0019 g = 1.9 x 10-3 g

  13. Review of the Mole: • a mole is a standard amount of a chemical substance. • Just as “a dozen” represents 12, a mole represents 6.02x1023 molecules. • the mole makes it possible for chemists to measure a given amount of a substance, or to compare amounts of different elements - otherwise, single atoms are far too small to see and measure.

  14. Review of Molar Mass: • each element on the periodic table has its own atomic mass. • the molar mass is the mass of an element (or compound) in grams per mole (g/mol) of that substance. • Ex. the molar mass of carbon is 12.01g/mol. That means that one mole of carbon weighs 12.01g.

  15. the molar mass of compounds can be calculated by adding up the molar masses of the composing elements • Ex. the molar mass of water, H2O is… • MH2O = 2 (MH) + 1(MO) • MH2O = 2(1.01g/mol) + 1 (16.00g/mol) • MH2O = 18.02g/mol

  16. The relationship between molar mass, number of moles and mass: • Recall the formula: • Rearrange the formulas: • To solve for “m” • To solve for “M” n = m M

  17. Figuring Out Molar Mass • For Elements: • Check periodic table • It will give you the number • Ex: Sodium (Na) • 22.99 g/mol • For Molecules: • Add up all of the elements in the molecule • Make sure you add up the TOTAL number of molecules • E.g., H2SO4 • 2H so 2 x 1.01 = 2.02 • 1S so 1 x 32.07 = 32.07 • 4O so 4 x 16.00 = 64.00 • = 2.02 + 32.07 + 64.00 = 98.09 g/mol

  18. Calculate the Molar Mass For the Following • A) NaHCO3 • B) NH4Cl • C) FeS2 • D) C6H12O6

  19. Calculating Molar Mass • http://www.youtube.com/watch?v=F9NkYSKJifs&safety_mode=true&persist_safety_mode=1&safe=active

  20. Assignment • P. 44 #32-33 • P. 17 of work booklet (i.e., Molar mass practice worksheet)

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