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Moles to grams conversions and % composition

Moles to grams conversions and % composition. Molar Mass. The mass in grams of 1 mole of a substance is called the molar mass of the substance. The molar mass of an element is equal to its atomic mass. The unit for molar mass is grams per mole, or g/mol. Molar Mass. Ne = 20.18 g/mol

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Moles to grams conversions and % composition

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  1. Moles to grams conversionsand % composition

  2. Molar Mass • The mass in grams of 1 mole of a substance is called the molar mass of the substance. • The molar mass of an element is equal to its atomic mass. • The unit for molar mass is grams per mole, or g/mol

  3. Molar Mass • Ne = 20.18 g/mol • O2 = 16.00*2 = 32.00 g/mol • U = 238.03 g/mol • NaOH = 22.99 + 16.00 + 1.008 = 40.00 g/mol • CO2 = 12.01 + 16.00*2 = 44.01 g/mol • Al2(CO3)3 = 26.98*2 + (12.01*3) + (16.00*9) = 233.99 g/mol

  4. Moles to Grams Conversions • If you know the mass of a substance, you can calculate the number of moles. • You have 11.2 g of NaCl. How many moles is that? • 1. determine the molar mass of NaCl (using the periodic table) • Na= 23.0 g/mol Cl= 35.5 g/mol • 23.0 g/mol + 35.5 g/mol = 58.5 g/mol (get these #’s from the periodic table)

  5. Moles to Grams Conversions • Molar mass of NaCl = 58.5 g/mol • Set up a conversion factor (a fraction whose value is equal to 1) • The units we need should be in the numerator and the units you already know in the denominator.

  6. Moles to Grams Conversions • You can also determine the mass of a sample if you know the number of moles • 2.50 mol of NaCl is how many grams? • Set up a conversion factor 

  7. Moles to Grams Conversions MASS • How many moles are in 14 g LiOH? • How many moles are in 15 g N2? moles x g = g mol Molar Mass g x mol = moles g MOLES 14 g LiOH 1 1 mol LiOH 23.95 g LiOH 0.58 mol LiOH 15 g N2 1 1 mol N2 28.02 g N2 0.54 mol N2

  8. Moles to Grams Conversions • How many grams are in 4 mol H2O2? • How many grams are in 56 mol CaCO3? 4 mol H2O2 1 34.016 g H2O2 1 mol H2O2 136.06 g H2O2 56 mol CaCO3 1 100.09 g CaCO3 1 mol CaCO3 5605.04 g CaCO3

  9. Multistep Conversions • You want to impress your date by boasting you know how many molecules of table sugar are in the cake you just made. You need 250 g of sugar (C12H22O11). How many sucrose molecules will be in the cake? • Plan: Convert the mass to moles using the molar mass and then convert to moles using Avogadro’s number. MASS PARTICLES Avogadro’s Number Use molar mass MOLES 250 g C12H22O11 1 1 mol C12H22O11 342.3 g C12H22O11 6.02x1023 molecules 1 mol C12H22O11 4.4x1023 molec. C12H22O11

  10. Multistep Conversions • If you burned 4.0x1024 molecules of methane (CH4) during a laboratory experiment, what mass of methane did you use? • Plan: Convert your given # of molecules to moles using Avogadro’s number, then convert the moles to grams using the molar mass of methane. (12.00 + 1.004*4) 4.0 x 1024 molec. CH4 1 1 mol CH4 6.02x1023 molec. CH4 16.016 g CH4 1 mol CH4 106.42 g CH4

  11. Percent Composition • You can determine what part of the total mass of a compound is made up by each element in that compound. • Percent Composition- the mass of each element in a compound compared to the entire mass of the compound and multiplied by 100 percent.

  12. Determining % Composition • First method: Calculate from a given formula • Example: Water • 1 mole of water (H2O) • Molar mass= 18 grams • 2 moles of hydrogen atoms • 1 mole of oxygen atoms • To determine percent composition you need to determine what part of the total mass, 18 g, is made up of hydrogen atoms and what part is made up of oxygen atoms.

  13. Determining % Composition % of element = total mass of element in compound 100 total mass of compound • % of hydrogen= 2.0 g H x 100 = 11% 18.0 g H2O • % of oxygen = 16 g O x 100 = 89% 18.0 g H2O

  14. Determining % Composition • Second method: Experimental analysis (mass the whole sample, separate into parts through decomposition, mass the parts, follow same method as before) • A sample of an unknown compound with a mass of 0.2370 g was extracted from the roots of a plant. Decomposition produced 0.09480 g of carbon, 0.1264 g of oxygen, and 0.0158 g of hydrogen. What is the percent composition of the compound? • Plan: Determine the % of each element in the compound by dividing the mass of each element by the total mass of the sample, then multiply by 100. • % C = (0.0948 g / 0.2370 g) x 100% = 40.00% C • % O = (0.1264 g / 0.2370 g) x 100% = 53.33% O • % H = (0.0158 g / 0.2370 g) x 100% = 6.67% H

  15. Your Turn • Find the percent composition of a compound that contains 2.30 g of sodium, 1.60 g of oxygen, and 0.100 g of hydrogen in a 4.00-g sample of the compound. • % Na = (2.30 g / 4.00 g) x 100% = 57.5% Na • % O = (1.60g / 4.00 g) x 100% = 40.0% O • % H = (0.100 g / 4.00 g) x 100% = 2.50% H

  16. B D Moles of substance Number of particles Mass of substance • Use N as a unit factor: multiply by 1 mol/6.02x1023 • Use N as a unit factor: multiply by 6.02x1023/1 mol • Use molar mass as a unit factor: multiply by 1 mol/#g • Use molar mass as a unit factor: multiply by #g/1 mol • Use molar volume as a unit factor: multiply by 1 mol/22.4L • Use molar volume as a unit factor: multiply by 22.4L/1 mol A C E F Volume of gas (STP)

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