The Mole: A Measurement of Matter Chapter 10.1 The Mole: A Measurement of Matter

Three ways of measuring things…count, mass, & volume. Examples: soda—6 pack soda—liter grapes--lbs

Terms for specific counts…pair, dozen, etc. 1 dozen apples = 12 apples. 1 dozen apples = 2.0 kg apples. 1 dozen apples = 0.2 bushels apples. Ratios: 1 dozen apples/12 apples 1 dozen apples/2.0 kg apples 1 dozen apples/0.2 bushels apples

Problem… What is the mass of 90 apples if 1 dozen apples = 2.0 kg? Analyze…known… # of apples = 90 12 apples = 1 dozen 1 dozen = 2.0 kg Unknown…mass of 90 apples = ?kg

Calculate

Evaluate Does it make sense? Practice…What is the mass of 0.5 bushels of apples? Practice…assume 8 seeds per apple. How many seeds are in 14 kg of apples?

What is a Mole? A specified number of particles. Used by chemists. 6.02 x 1023 representative particles (Avagrado’s number). Representative particles can be atoms, molecules, or formula units. Ratio: 1 mole/6.02x1023 rep. particles

Scientific basis of the mole 6.02x1023 is the number of atoms in 12 grams of Carbon-12. If one mole of carbon-12 atoms were weighed, it would weigh exactly 12 grams.

Atoms to moles How many moles in 1.25x1023 atoms of magnesium? Known; # of atoms = 1.25x1023 1 mole = 6.02x1023 atoms Mg. Unknown; moles of magnesium. Calculate…

Moles to # of particles How many atoms in a mole? First determine how many atoms in a representative particle. How many atoms in 2.12 moles of propane (C3H8)? Known: # of moles of C3H8 is 2.12. 1 mole = 6.02x1023 molecules C3H8. 1 molecule C3H8 = 11 atoms. Unknown: # of atoms.

Calculate… Practice… How many atoms in 1.14 moles SO3? How many moles in 4.65x1024 molecules NO2?

The Mass of a Mole of an Element Mass of atoms expressed in amu’s (atomic mass units), which are relative units based on the isotope Carbon-12 (12.0 amu). C-12 is twelve times heavier than an average hydrogen atom with a mass of 1.0 amu. 100 C-12 atoms are 12 times heavier than 100 hydrogen atoms.

Any number of C-12 atoms are always twelve times heavier than the same number of hydrogen atoms. The mass ratio of 12 carbon atoms to 1 hydrogen atom is the same regardless of the units used to express the mass. Therefore, 12.0 g of carbon atoms and 1.0 g of hydrogen atoms must have the same number of atoms.

Representative Particle Smallest unit in a substance Can be different things One atom (metals, atomic substances) One molecule (molecular compounds) One ion (charged atoms or molecules) One formula unit (ionic compounds)

Examples of Representative particles Substance Representative particle Formula Iron atom Fe Atomic nitrogen N Nitrogen gas molecule N2 water H2O Calcium ion ion Ca2+ Calcium fluoride Formula unit CaF2 glucose C6H12O6

Measuring Chemical Substances Using Avogadro’s number: a specific number of representative particles 6.02 x 1023 RP/mole Referred to as one mole (mol) Example: One mol water contains 6.02 x 1023 H20 molecules Example: one mole nitrogen gas…

Practice Q: how many moles does 1.25 x 1023 atoms of Mg represent? A: 1.25 x 1023 Mg atoms x (6.03 x 1023 RP)/mole = 0.2 moles Q: how many moles does 2.8 x 1024 atoms of silicon have? A: 2.8 x 1024 Si atoms/6.03 x 1023 RP/mole = 4.6 moles Q:Q: How many propane (C3H8) molecules are in 2.12 mol of C3H8 ? A: 2.12 moles x (6.03 x 1023 ) RP/mole = 12.8

Converting molecular Moles into Number of individual atoms Hint: when asked for # of atoms always do Moles #molecules #atoms

Practice Q: How many atoms are in 2.12 mol of C3H8 ? First calculate how many molecules A: 2.12 moles x (6.02 x 1023 RP)/mole= 12.76 x 1023 RP = 1.28 x 1024 RP Then calculate how many atoms Each RP (C3H8) has 11 atoms/RP Multiply with 11: 1.28 x 1024 RP x 11 Atoms/Rp= 14.08 X 1024 atoms Clean all results to single digit number!!! 14.08 X 1024 → Atoms = 1.4 x 1025 atoms

Practice You have 4.65 x 1024 molecules of NO2? Q: How many atoms? A: RP NO2 has three atoms/molecule 3 atoms/molecule x 4.65 x 1024 molecules

The mass of one mole of a given element Mass of an element is indicated in the periodic table as the mass number Called amu = atomic mass unit amu is the mass (in grams) of one mole of this element Remember it is an average number of the different isotopes…it has decimals

Finding mass What is the mass of one mole O, P, K, S-33, 146C Atomic oxygen: 16.00 g/mole Atomic phosphorus: 30.97 g/mole Atomic potassium: 39.10 g/mole Atomic S-33: 33.00 g/mole Atomic 146C: 14.00 g/mole

How many mole in a given mass How many moles of Carbon are found in 52 g? 52 g/12.01 g/mole C= 4.33 moles C

Practice calculating molar masses Q: How many moles of C-14 are found in 34 g? 34 g x mole C-14/14g C-14 = 2.42 moles C-14 Q: What mass does 6.02 x 1023 atoms of Hydrogen have? Is one mole → 1.01 g Q: What is the mass of 2.34 x 1022 atoms of phosphorus? First find how many moles 2.34 x 1022 atoms x mole/6.02 x 1023 atoms = 0.04 moles P 0.04 moles P x 30.97 g/mole = 1.24 g

Mass of a Mole of a Compound Example: SO3 What type of compound? How many atoms of S and O? Add up amus of S and O 32.1 amu + 16.0 amu +16.0 amu + 16.0 amu = 80.1 amu One mole SO3 weighs 80.1 g

Practice: find the molar masses Find the molar mass of Water Glucose Carbon dioxide

Practice Q:How many moles of glucose are in 200 g? Molar mass of glucose is 180.18 g/mole A: 200g x mole/180.18 g = 1.11 moles Q: How many molecules of glucose is this? 6.02 x1023 RP/mole x 1.11 moles = 6.7 x 10 23 molecules glucose