AP Chemistry Ch. 4. When ionic substances (salts) dissolve, they break up into. 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes

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1 Name AP Chemistry Ch. 4 Aqueous solution 4.1 Water, the Common Solvent Water (a.k.a ) Why is water such a good solvent? Hydration When ionic substances (salts) dissolve, they break up into ions. Why is NaCl very soluble and AgCl is only slightly soluble? Water also dissolves many nonionic substances. (Ethanol) Why? Water does not dissolve everything. The rule is 4.2 The Nature of Aqueous Solutions: Strong and Weak Electrolytes Electrical conductivity Strong Electrolytes Soluble Salts Strong Acids H 2 SO 4, HNO 3, HCl, HBr, and HI are Dissolve into ions ( %) H 2 SO 4 - only H + is completely dissociated. The other H + will only dissociate under special circumstances. Strong Bases

2 Weak Electrolytes Most common = Acetic Acid NH 3 Nonelectrolytes Often are 4.3 The Composition of Solutions We must know: 1) 2) Molarity ( ) What is the molarity of a 2.25 L solution containing 10.0 g of KOH? Give the concentration of each type of ion in 0.5 M Ca(NO 3 ) 2 You can also use M to find moles (and thus, grams of solute). How many grams of NaOH are contained in ml of a M NaOH solution?

3 Standard solution Fig 4.10, p. 143 Dilution Stock solution Key = M 1 V 1 = M 2 V 2 How would you prepare 1.00 L of a 0.50 M solution of HCl from a concentrated (12 M) stock solution? 4.4 Types of Chemical Reactions Reactions Reactions Reactions ( )

4 4.5 Precipitation Reactions precipitate Remember our dime lab. The dime was an alloy (mixture) of and. We dissolved the dime in acid. Key = when a solid dissolves the ions and move independently. What ions do we have in our dime solution? Our goal was to isolate the silver. We did this by using to precipitate AgCl. To the above ions we now also have What precipitate forms? Why? Don t forget: You MUST memorize the solubility rules! (p. 144) 4.6 Describing Reactions in Solution - gives the overall reaction stiochiometry, but not necessarily the actual forms of reactants and products. - represents as ions all reactants and products that are strong electrolytes. - includes only those slultion components undergoing a change. Spectator ions are NOT included. Give the molecular, complete ionic, and net ionic equations for the following: Molecular: HCl + NaOH Complete Ionic: Net Ionic:

5 Stoichiometry of Precipitation Reactions You need to make sure you understand what is happening in the reaction. You may need to use molarity (M) to determine a necessary piece of information. What volume of M Na 3 PO 4 is required to precipitate all the lead (II) ions from ml of M Pb(NO 3 ) 2? 4.8 Acid-base Reactions Arrhenius Acid = Base = Bronsted-Lowery Acid = Base = When acids react with bases is formed: net ionic equation: OH - is such a strong base that it will react with any weak acid. Neutralization Reaction A ml sample of HCl requires ml of M NaOH for complete neutralization. What is the concentration of the original HCl solution?

6 Acid-base Titrations Three requirements for a successful titration: (see p. 152) Oxidation-Reduction Reactions (Redox) Redox rxns are when are transferred. oxidation states (numbers) provide a way to track See the rules on p Summarize them. 1. element = 2. monatomic ion = 3. fluorine is always = 4. oxygen is usually = 5. hydrogen is generally = 6. sum of ox. numbers of a neutral compound = 7. sum of ox. numbers for an ion = Assign oxidation states for: KMnO 4 UO 2 2+ Ca(NO 3 ) 2 oxidation reduction LEO says GER = Loss of Electrons, Oxidation. Gain of Electron, Reduction oxidizing agent reducing agent

7 Specify the oxidizing agent, reducing agent, substance being oxidized and substance being reduced: CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O (g) 4.10 Balancing Oxidation-Reduction Reactions Depends on whether the reaction occurs in acidic or basic solution. For rxns in ACIDIC conditions: Step 1 Write separate reactions for and Step 2 Balance each Balance all elements except and Balance oxygen using H 2 O Balance hydrogen using H + Balance charge using e - Step 3 Multiply each half-reaction to equalize the number of Step 4 Add the, cancel identical Step 5 Check that elements and charges are balanced. For rxns in BASIC conditions: Step 1 Write separate reactions for and (just like acids pretend H + present) Step 2 Add OH - to both sides to eliminate H + by forming H 2 O Step 3 Eliminate the that appear on both sides of the equation. Step 4 Check that elements and charges are balanced. See Sample Exercises 4.19 and 4.20, p