Presentation on theme: "Chemical Quantities (the MOLE) Chapter 10. Counting Units How many is a dozen? How many does the word “couple” stand for? How many sheets are in."— Presentation transcript:
Counting Units How many is a dozen? How many does the word “couple” stand for? How many sheets are in a ream of paper? Answers: 12, 2, 500
Chemist’s “Dozen” Chemists also have a counting unit for a certain number of things A mole = Avogadro’s number of things 1 mole = 6.02 x 10 23 things –Could be atoms, ions, particles, molecules, etc. How big is that number? –See Sheet: A mole is a lot of things
Sample Problem How many atoms are contained in 4.5 moles of copper? How many moles are in 8.3 x 10 24 molecules of water? Answers: 2.71 x 10 24 atoms, 13.8 moles
Masses and Moles If you had a dozen bowling balls and a dozen ping pong balls, which would have more mass? Why? The bowling balls would have more mass because each individual bowling ball has more mass than a ping pong ball.
Mass of Elements and Moles Which would be heavier: a mole of copper or a mole of lead? Why? A mole of lead would be heavier because an atom of lead is heavier than an atom of copper (64 amu vs. 207 amu)
Carbon-12 and Avogadro’s Number Avogadro’s number is related to the mass of an element, specifically carbon (the isotope carbon-12) Used exactly 12 grams of carbon and determined the number of atoms in that sample There are 6.02 x 10 23 atoms in 12 grams of carbon (1 mole)
Definition of Mole A mole is the amount of matter that contains as many objects (atoms, molecules, etc.) as the number of atoms in exactly 12 g of 12 C. –Mole connects amu & gram = “Chemists dozen”
Molar Mass How do you determine moles if you have a compound? What is the mass of 1 mole of NaCl? Answer: 58 g/mol Molar Mass: the mass of one mole of a substance (element or compound)
Sample Problem- molar mass What is the mass of one mole of –water? –Carbon dioxide? –C 6 H 12 O 6 (glucose) –Ca(NO 3 ) 2 –Answers: 18 g/ mol, 44, 180, 164
Sample Problem- moles to mass How many grams of sodium chloride (NaCl) did you use if you put 0.250 moles of it on your French fries? Answer: 14.5 g
Sample Problem – mass to moles How many moles of helium are in a balloon that contains 4.5 g of helium? Answer: 1.1 moles
Molar Volume Can you determine moles from the volume of a substance? –For solids and liquids: must use density –For gases: related to the temperature and pressure of the gas.
Avogadro’s Hypothesis Equal volumes of gases at the same temperature and pressure contain the same number of molecules All gases behave the same way, no matter the chemical identity
Standard Temp and Pressure Because the volume of a gas depends on the temp and pressure of the gas, a standard reference is necessary STP: Standard Temperature and Pressure –Std Temp: 0 o C or 273 K –Std Press: 101.3 kPa or 1 atm 1 mole of a gas at STP = 22.4 L
Sample Problem – Volume to moles How many moles of helium are in a balloon has a volume of 6.40 L? (at STP) Answer:.286 moles
Study Buddy Review What is Avogadro’s Number? What is a mole? What is molar mass? How do you find the molar mass of a compound? What is STP?
Penny Composition Remember: a penny’s composition has changed through the years –Most recent change 1982 If a post-1982 penny is 2.500 g and it has 0.0625 g copper, what percentage is copper? What percentage is zinc? Answers: 2.50 % Cu, 97.50 % Zn
Percent Composition mass of each element in compound compared to the entire mass of the compound, multiplied by 100%
Sample Problem What is the percentage composition of copper in chalcocite, Cu 2 S? Answer: 80 %
Consider these C 6 H 12 O 6 glucose (blood), fructose (corn syrup) C 5 H 10 O 5 ribose (RNA), xylose What do the formulas have in common?
Empirical formulas CH 2 Osmallest whole number ratio Carbohydrates: C n (H 2 O) n Empirical Formulas: smallest whole number ratio of the atoms in a substance
Molecular Formulas Molecular Formula: whole number multiple of empirical – –tells the actual number of atoms in a substance as it exists in nature –Can be the same as the empirical formula