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Published byGodfrey Farmer Modified over 9 years ago
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Warmup (5 minutes) 1. A “dozen” is what we call a “counting unit.” What are some other counting units? 2. Write the formula for aluminum sulfate 3. Do atoms ever disappear from our universe?
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Equations and the Mole You will have another Memorization Quiz next class: ions again, and solubility rules too!
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In science, a mole is how we count the number of a substance (like a dozen).
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How much is a mole? The number of things in 1 mole has been determined to be: 6.02 x 10 23 This is Avogadro’s Number (after the scientist who figured it out). 602000000000000000000000 is the number of atoms in 12 grams of carbon.
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Is one mole always the same quantity? 1 mole silicon atoms 1 mole iodine atoms Mass = 28.09 gramsMass = 126.90 grams 6.02x10 23 atoms in each box Yes: for # molecules or atoms No: for mass
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2Na(s) + 2H 2 O(l) → 2NaOH(aq) + H 2 (g) solidliquidaqueous gas 2 moles1 mole (no #) ReactantsProducts arrow = “yield”, “make”, “produce”, “form” Translate the equation into a sentence! 2 moles of solid sodium react with 2 moles of liquid water to yield 2 moles of aqueous sodium hydroxide and 1 mole of hydrogen gas (Why H 2 ?)
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Diatomic Elements are: gaseous elements which are unstable if found as a single atom; H 2 O 2 F 2 Br 2 I 2 N 2 Cl 2 Write an equation: 2 moles of solid sodium react with 1 mole of chlorine gas to yield 2 moles of aqueous sodium chloride 2Na(s) + Cl 2 (g) 2NaCl(aq)
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Write the equation: solid calcium reacts with aqueous hydrogen chloride to yield aqueous calcium chloride and hydrogen gas Ca(s) + HCl(aq) → CaCl 2 (aq) + H 2 (g) Is this equation balanced? Law of conservation of matter: in a chemical reaction, matter is neither created nor destroyed 1 1 21
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A balanced equation obeys this law; it has equal numbers of each type element on both sides of the equation. “what goes in, comes out!” _____H 2 + _____ O 2 _____ H 2 O 122
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Balancing Tips 1) Use a pencil, you might have to erase! 2) It helps to balance metal atoms first, H’s and O’s last! 3) Place whole-number coefficients in front of the formulas; NEVER change subscripts in the chemical formula. “1” is not completely necessary. 4) Multiply new coefficient times the subscript to count the total # atoms for that element on each side. (Example: 2H 2 = 4 hydrogen atoms total) It takes practice…you will not learn by watching!
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__Al (s) + __Fe 2 O 3 (aq) → __Al 2 O 3 (aq)+ __Fe(s) Balancing Example: #1 2 211 AlOFe OOAl OOOFe Al
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__C 2 H 4 + __O 2 → __CO 2 + __H 2 O 2 minutes! 22 3 1 ____ N 2 + ____ H 2 ____ NH 3 2 3 1
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Be Careful With Parentheses: How many atoms are in: Mg(OH) 2 3Mg(OH) 2 # of Mg atoms: # of O atoms: # of H atoms: 1 3 26 2 6 3Mg(OH 2 ) 2 3 6 12
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A hamburger is made of certain materials: Bun Lettuce Meat Bun What would an equation for the synthesis of one hamburger look like? ____Bun + ____Lettuce + ____Meat ____hamburger 2111
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Mole Ratio Problems If I wanted to make 20.5 hamburgers, how many buns would I need? ____Bun + ____Lettuce + ____Meat ____hamburger 2111 20.5 hamburger (1 hamburger) (2 buns) = 41.0 buns How many hamburgers can I make if I had 17 meats (assuming I have enough of everything else)? 17 meats (1 meat) (1 hamburger) = 17 hamburgers
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1N 2 + 3H 2 2NH 3 Translate the equation above into a sentence: If 1 mole N 2 reacts with 3 moles H 2, 2 moles NH 3 are produced. Write all the molar ratios possible given this equation The molar ratio compares the number of moles of each compound in an equation. I will sometimes say ‘molecules’ to simplify, although this is technically inaccurate. 1 mole N 2 3 moles H 2 1 mole N 2 3 moles H 2 1 mole N 2 2 moles NH 3 2 moles NH 3 3 moles H 2 2 mole NH 3 1 mole N 2 2 moles NH 3 3 moles H 2
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If 2 moles of N 2 are used, how many moles of NH 3 will be produced in the reaction? 1N 2 + 3H 2 2NH 3 2 moles N 2 (2 moles NH 3 ) = 4 moles NH 3 (1 mole N 2 ) If you want 7.70 moles of NH 3, how much H 2 is needed? 7.70 moles of NH 3 (3 moles H 2 ) = (2 moles NH 3 ) 11.6 moles H 2 Warning: Sometimes you will have to balance the equation first!
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