# What_to_know_for_Exam_2_with_Vocab (1).docx - What to Know...

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What to Know for Exam 2 1. A mole is 6.022x10 23 (N A ). 2. Molar Mass: Converting: (moles)x(MM) = grams. ( grams MM ) = moles (mole)x(N A ) = number or atoms or molecules. Be able to go from grams to moles to molecules to total atoms. 3. Percent composition (for each element in a compound) = MM of the element MM of the totalcompound x 100 4. Empirical Formula: Simplest ratio of each element in the compound. To determine empirical formula: (If the composition is given in percent by mass, assume 100 grams and then:) 1. Find moles of each element: [ ( grams MM ) = moles] 2. Divide each of the moles by the smallest number of moles. 3. If you do not get a whole number for each, multiple by some value n to get whole numbers. (If you get _.5 moles, multiple by 2… if you get _.33 multiple by 3, etc.) To determine the molecular formula: (empirical formula)x(n) = molecular formula MM molecular formula MM empirical forumla = n 5. Know solutions.. know the components: solute and solvent. Know Molarity Molarity = molessolute Volume of solution L 6. Know Dilution: (assuming that moles of solute are constant) V 1 M 1 = V 2 M 2 This also works for any units of concentration: V 1 C 1 = V 2 C 2 7. Be able to use the solubility rules to predict precipitates and spectator ions. Know: Strong electrolyte, weak electrolyte, strong acid and base and weak acid and base. a) Precipitation. Formation of an insoluble ionic compound. b) Acid/Base. Transfer of an H + in a reaction. If you make a salt and water.. this is neutralization.
c) Redox. Transfer of electrons. Know the solubility Rules (For ionic compounds in water) These are usually soluble (dissociates into its ions) Li + , Na + , K + , NH 4 + No exceptions NO 3 - and C 2 H 3 O 2 - No exceptions Cl - , Br - , I - EXCEPT: insoluble with Ag + , Pb 2+ and Hg 2 2+ SO 4 2- EXCEPT: insoluble with Ca 2+ , Ba 2+ , Sr 2+ , Pb 2+ , Ag + These are usually insoluble (make solids) CO 3 2- and PO 4 3- EXCEPT: soluble with Li + , Na + , K + , NH 4 + S 2- EXCEPT: soluble with Li + , Na + , K + , NH 4 + , Ca 2+ , Ba 2+ , Sr 2+ OH - EXCEPT: soluble with Li + , Na + , K + , NH 4 + , and somewhat soluble with Ca 2+ , Ba 2+ , Sr 2+ 8. Write balanced molecular equations, total ionic equations and net ionic equations. A soluble ionic compound is 100 % dissociated in water. It will break into its ions and be a strong electrolyte. An insoluble ionic compound remains as a solid. Many ionic compounds are slightly soluble and dissociate into a few ions in water. Be able to write the molecular equation, total ionic equation and net ionic equation for precipitation and acid/base reactions. If Na 2 CO 3 (aq) reacts with CaCl 2 (aq) the reactions are: Molecular: Na 2 CO 3 (aq) + CaCl 2 (aq) 2NaCl(aq) + CaCO 3 (s) Total ionic: 2Na + (aq) + CO 3 2- (aq) + Ca 2+ (aq) + 2 Cl - (aq) 2Na + (aq) + 2 Cl - (aq) + CaCO 3 (s) Net ionic: CO 3 2- (aq) + Ca 2+ (aq) CaCO 3 (s) (The 2Na + (aq) + 2 Cl - (aq) are not included in the net ionic reaction because they are spectator ions.) Remember that if an ionic compound is soluble it is broken into its ions. CaCl 2 (aq) is written as Ca 2+ (aq) and 2 Cl - (aq).

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