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Mole & Chemical Composition Honors chemistry – Semester 1
Converting between grams, moles and number of particles
Avogadro's Number
• The number of particles present in 1 mol of substance Avogadro’s Number (NA)
• 1 mol of pure substance = 6.022 x 1023 particles
• Avogadro’s number can be used to count ANY kind of particle, including atoms, molecules, ions, photons …
Sample Problem – converting moles to number of particles
Find the number of molecules in 2.5 mol of sulfur dioxide.
Solution:
• Conversion path: • mol multiply by Avogadro’s number # of particles
• 2.5 mol SO2 x 6.022 x 1023 molecules SO
2
1 mol SO2
= 1.5 x 1024 molecules SO2
Practice Problems
• How many ions are there in 0.187 mol of Na+ ions?
• 1.13 x 1023 ions of Na+
• How many atoms are there in 1.45 x 10-17 mol of arsenic?
• 8.73 x 106 atoms As
• How many molecules are there in 4.224 mol of acetic acid, CH3COOH?
• 2.544 x 1024 molecules CH3COOH
Sample Problem – converting number of particles to moles
A sample contains 3.01 x 1023 molecules of SO2. Determine the amount in moles.
Solution:
• Conversion Path:
• number of particles divide by Avogadro’s Number mole
• 3.01 x 1023 molecules SO2 x 1 𝑚𝑜𝑙 𝑆𝑂
2
6.022 𝑥 1023 𝑚𝑜𝑙𝑒𝑐𝑢𝑙𝑒𝑠 𝑆𝑂2
= 0.500 mol SO2
Practice Problems
• How many moles of xenon do 5.66 x 1023 atoms equal?
• 0.940 mol Xe
• How many moles of silver nitrate do 2.888 x 1015 formula units equal?
• 4.796 x 10-9 mol AgNO3
• A biologist estimates that there are 2.7 x 1017 termites on Earth. How many moles of termites is this?
• 4.5 x 10-7 mol termites
Converting between Moles and Grams • Use molar mass of a substance
• Molar mass = the mass in grams of 1 mol of a substance (unit: g/mol)
• Atomic mass (amu) same number as molar mass (grams)
• Example: atomic mass of copper is 63.5 amu molar mass of copper is 63.5 g/mol
Sample Problem – converting number of particles to mass Find the mass in grams of 2.44 x 1024 atoms of carbon,
whose molar mass is 12.0 g/mol.
Solution:
• Conversion path: • Divide number of particles by Avogadros’ Number moles
• Multiply moles by molar mass grams
• 2.44 x 1024 atoms C x 1 mol C
6.022 x 1023 atoms C x
12.0 g C1 mol C
= 48.6 g C
Practice
Find the mass in grams of each of the following:
• 2.11 x 1024 atoms of copper
• 222 g Cu
• 3.01 x 1023 formula units of NaCl
• 29.2 g NaCl
• 3.990 x 1025 molecules of CH4
• 1060 g CH4
Sample Problem – Converting Mass to Number of Particles Find the number of molecules present in 47.5 g of glycerol, C3H8O3.
The molar mass is 92.1 g/mol Solution: • Conversion path:
• Divide grams by molar mass moles • Multiply moles by Avogadro’s number number of particles
• 47.5 g glyc. x 1 mol glyc.92.1 g glyc.
x 6.022 x 1023 molecules glyc.
1 mol glyc. =
3.11 x 1023 molecules glycerol
Practice
• Find the number of atoms in 237 g Cu
• 2.25 x 1024 atoms Cu
• Find the number of ions in 20.0 g Ca2+
• 3.00 x 1023 ions Ca+
• Find the number of atoms in 155 mol of arsenic.
• 9.33 x 1025 atoms As