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Chapter 10.1 The Mole: A Measurement of Matter

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

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► 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

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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

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Calculate

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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?

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What is a Mole? ► A specified number of particles. Used by chemists x representative particles (Avagrado’s number). ► Representative particles can be atoms, molecules, or formula units. ► Ratio: 1 mole/6.02x10 23 rep. particles

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Scientific basis of the mole ► 6.02x10 23 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.

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Atoms to moles ► How many moles in 1.25x10 23 atoms of magnesium? ► Known; # of atoms = 1.25x10 23 ► 1 mole = 6.02x10 23 atoms Mg. ► Unknown; moles of magnesium. ► Calculate…

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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 (C 3 H 8 )? ► Known: # of moles of C 3 H 8 is mole = 6.02x10 23 molecules C 3 H 8. 1 molecule C 3 H 8 = 11 atoms. ► Unknown: # of atoms.

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► Calculate… ► Practice… ► How many atoms in 1.14 moles SO 3 ? ► How many moles in 4.65x10 24 molecules NO 2 ?

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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.

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► 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.

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Representative Particle ► Smallest unit in a substance ► Can be different things 1. One atom (metals, atomic substances) 2. One molecule (molecular compounds) 3. One ion (charged atoms or molecules) 4. One formula unit (ionic compounds)

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Examples of Representative particles Substance Representative particle Formula IronatomFe Atomic nitrogen atomN Nitrogen gas molecule N2N2N2N2 watermolecule H2OH2OH2OH2O Calcium ion ion Ca 2+ Calcium fluoride Formula unit CaF 2 glucosemolecule C 6 H 12 O 6

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Measuring Chemical Substances ► Using Avogadro’s number: a specific number of representative particles 6.02 x RP/mole ► Referred to as one mole (mol) Example: One mol water contains ► 6.02 x H 2 0 molecules Example: one mole nitrogen gas…

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Practice Q: how many moles does 1.25 x atoms of Mg represent? A: 1.25 x Mg atoms x (6.03 x RP)/mole = 0.2 moles Q: how many moles does 2.8 x atoms of silicon have? A: 2.8 x Si atoms/6.03 x RP/mole = 4.6 moles Q:Q: How many propane (C 3 H 8 ) molecules are in 2.12 mol of C 3 H 8 ? A: 2.12 moles x (6.03 x ) RP/mole = 12.8

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

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Practice Q: How many atoms are in 2.12 mol of C 3 H 8 ? ► First calculate how many molecules A: 2.12 moles x (6.02 x RP)/mole= x RP = 1.28 x RP ► Then calculate how many atoms Each RP (C 3 H 8 ) has 11 atoms/RP Multiply with 11: 1.28 x RP x 11 Atoms/Rp= X atoms ► Clean all results to single digit number!!! X → Atoms = 1.4 x atoms

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Practice You have 4.65 x molecules of NO 2 ? Q: How many atoms? A: RP NO 2 has three atoms/molecule 3 atoms/molecule x 4.65 x molecules

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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

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Finding mass ► What is the mass of one mole O, P, K, S- 33, 14 6 C ► Atomic oxygen: g/mole ► Atomic phosphorus: g/mole ► Atomic potassium: g/mole ► Atomic S-33: g/mole ► Atomic 14 6 C: g/mole

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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

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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 atoms of Hydrogen have? ► Is one mole → 1.01 g Q: What is the mass of 2.34 x atoms of phosphorus? First find how many moles 2.34 x atoms x mole/6.02 x atoms = 0.04 moles P 0.04 moles P x g/mole = 1.24 g

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Mass of a Mole of a Compound ► Example: SO 3 ► What type of compound? ► How many atoms of S and O? ► Add up amus of S and O ► 32.1 amu amu amu amu = 80.1 amu ► One mole SO 3 weighs 80.1 g

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

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Practice Q:How many moles of glucose are in 200 g? ► Molar mass of glucose is g/mole A: 200g x mole/ g = 1.11 moles Q: How many molecules of glucose is this? 6.02 x10 23 RP/mole x 1.11 moles = 6.7 x molecules glucose

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