9/24/09 Chem 111 Experiment #7 Solutions and Reactions Brown, LeMay, and Bursten Chapter

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1 Chem 111 Experiment #7 Solutions and Reactions Brown, LeMay, and Bursten Chapter KEY VOCABULARY: 1. Ionic compound a compound composed of cations (+) and anions (-). Many ionic compounds dissociate (break apart) in water into their component ions. This enables the solution to conduct electricity. The ionic compound is then called an electrolyte. Example: NaCl Some strongly charged ions will not break apart in the presence of water. Example: (Ca) 3 (PO 4 ) 2 Solubility rules help to identify this property. 2. Molecular compound a compound that is held together by covalent bonds (bond where electrons are shared between atoms). In water, molecular compounds may dissolve, but they do not break apart into ions. Therefore, they are nonelectrolytes. Nonelectrolytes will not conduct electricity. Example: Sucrose (C 12 H 22 O 11 ) 1

2 Polar vs. Non-polar molecules a. A polar bond is one where one atom of the molecule attracts the bonding electrons more than the other. Partial positive and negative charges on the atoms are created. Example: O is more electronegative than H. 2 e - are closer to O. b. A nonpolar bond is one where the atoms of the molecule equally share the bonding electrons. Example: H & C are pulling equally on e-. c. A polar molecule has polar bond(s) and an unsymmetrical shape. VS. Water has polar bonds and is unsymmetrical. This makes it a polar molecule. Carbon tetrachloride has polar bonds, but the symmetrical shape makes it nonpolar. 2

3 3. Solution a homogeneous mixture of 2 or more substances. a. No visible layers or suspended particles are seen. b. The substance present in the greatest quantity is the solvent. c. The other substances in the solution are called solutes. 4. Precipitate an insoluble solid formed as a product in a reaction. a. This type of reaction is called a precipitation reaction. b. The precipitate formed will be determined by the solubility rules. Example: BaCl 2 (aq) + K 2 SO 4 (aq) BaSO 4 (s) + 2KCl(aq) We know that BaSO 4 is the precipitate because the solubility rules state that sulfates are soluble except when they are combined with strontium, barium, mercury(i), and lead(ii). 5. Exchange (metathesis) reaction reactions in which positive and negative ions switch places. This pattern is common in precipitation reactions and acid-base reactions. 6. Molecular equation a reaction equation which shows the complete chemical formulas of all reactants and products. Ex. AgNO 3 (aq) + HCl(aq) AgCl(s) + HNO 3 (aq) 3

4 7. Complete (or full) ionic equation a reaction equation which shows all soluble compounds in their ionic forms. Ex.Ag + (aq)+ NO 3 - (aq) + H + (aq) + Cl - (aq) AgCl(s) + H + (aq) +NO 3 - (aq) 8. Net ionic equation a reaction equation which removes all spectator ions leaving only the ions and molecules directly involved in the reaction. Ex. Ag + (aq) + Cl - (aq) AgCl(s) 9. Acid (Bronsted) a substance capable of donating an H + ion. Ex.: HCl 10. Base (Bronsted) a substance that will accept an H + ion. Ex.: NaOH 11. Strong acid/base an acid/base that readily breaks apart into its ions in water. Strong electrolytes Ex.: NaOH(aq) Na + (aq) + OH - (aq) 12. Weak acid/base an acid/base that does not readily break apart into its ions in water. Weak electrolytes Ex.: CH 3 COOH(aq) H + (aq) + CH 3 COO - (aq) 13. Neutralization reaction acid + base salt + water Ex.: HCl(aq) + NaOH(aq) NaCl(aq) + H 2 O(l) 4

5 When some salts react with water, they form acidic or basic species. 14. An acidic cation is a positively charged ion that produces H + ions (Arrhenius Acid) when it reacts with water. Example: Al 3+ (aq) + H 2 O(l) AlOH 2+ (aq) + H + (aq) 15. A basic anion is a negatively charged ion that produces OH - (Arrhenius Base) when it reacts with water. Example: CO 3 2- (aq) + H 2 O(l) HCO 3 - (aq) + OH - (aq) 5

6 5 CLASSES OF REACTIONS: **In Experiment #7, the emphasis will be on precipitation and acid/base reactions.** 1. Acid/Base: Acids react with bases to produce a salt and water. These are also called neutralization reactions. Molecular: H 2 SO 4 (aq) + 2 KOH(aq) K 2 SO 4 (aq) + 2 H 2 O(l) Full Ionic:2H + (aq)+so 4 2- (aq)+ 2K + (aq)+2oh - (aq) 2K + (aq)+ SO 4 2- (aq)+ 2H 2 O(l) Net Ionic: H + (aq) + OH - (aq) H 2 O(l) This is the net ionic equation most acid-base reactions. 2. Precipitation: Forms an insoluble product. Molecular: 2KCl(aq)+Pb(NO 3 ) 2 (aq) 2KNO 3 (aq) + PbCl 2 (s) Full: 2K + (aq)+2cl - (aq)+ Pb 2+ (aq)+ 2NO 3 - (aq) 2K + (aq)+2no 3 - (aq)+ PbCl 2 (s) Net Ionic: Pb 2+ (aq) + 2Cl - (aq) PbCl 2 (s) 6

7 3. Redox: Chemical species change oxidation states. Loss of electrons is oxidation. Gain of electrons is reduction. Molecular: Sn(s) + 2HCl(aq) SnCl 2 (aq) + H 2 (g) Full Ionic: Sn 0 (s)+2h + (aq)+2cl - (aq) Sn 2+ (aq) +2Cl - (aq) +H 2 0 (g) Net Ionic: Sn(s) Sn 2+ (aq) + 2e - Oxidation 2H + (aq) + 2e - H 2 (g) Reduction Sn(s) + 2H + (aq) Sn 2+ (aq) + H 2 (g) 4. Complexation: Forms a complex ion - a metal ion with other substances covalently bonded to it. Molecular: Fe(NO 3 ) 3 (aq)+4nh 3 (aq) Fe(NH 3 ) 4 (NO 3 ) 3 (aq) Full Ionic: Fe 3+ (aq)+3no 3 - (aq)+4nh 3 (aq) Fe(NH 3 ) 4 3+ (aq) + 3NO 3 - (aq) Net Ionic: Fe 3+ (aq) + 4NH 3 (aq) Fe(NH 3 ) 4 3+ (aq) 7

8 5. No Reaction: Occurs when all reactants form soluble products. Molecular: 2KNO 3 (aq)+ MgBr 2 (aq) Mg(NO 3 ) 2 (aq) + 2KBr(aq) Full:2K + (aq)+2no 3 - (aq) +Mg 2+ (aq)+2br - (aq) Mg 2+ (aq)+2no 3 - (aq) + 2K + (aq)+ 2Br - (aq) Net Ionic: No Reaction 8

9 Solubility Rules (taken from PSU Chemtrek p. 7-7) SOLUBLE: All ammonium (NH + 4 ) and Group 1A salts (Li +, Na +, K +, Rb +, Cs + ) All nitrates (NO - 3 ) and acetates (CH 3 COO - ) Most chlorides (Cl - ), bromides (Br - ), and iodides (I - ) EXCEPT Ag, Hg, and Pb Most sulfates (SO 2-4 ) EXCEPT Ag, Hg, Pb, Ca, Sr, and Ba INSOLUBLE: Most carbonates (CO 3 2- ) EXCEPT ammonium (NH 4 + ) and Group 1A salts Most phosphates (PO 4 3- ) EXCEPT ammonium (NH 4 + ) and Group 1A salts Most oxides (O 2 - ) EXCEPT ammonium (NH 4 + ) and Group 1A salts Most hydroxides (OH - ) EXCEPT ammonium (NH 4 + ), Group 1A salts, Ca, Sr, and Ba Most sulfides (S 2- ) EXCEPT ammonium (NH 4 + ), Group 1A salts, Ca, Sr, and Ba 5 CLASSES OF REACTIONS: Acid/Base: In most cases, neutralization reactions have a net ionic reaction of H + (aq) + OH - (aq) H 2 O(l) Precipitation: Forms an insoluble product. Redox: Species change oxidation states. o Loss of electrons is oxidation. o Gain of electrons is reduction. Complexation: Forms a complex ion - a metal ion with other substances covalently bonded to it. No Reaction: Occurs when all reactants form soluble products. 9

A reaction in which a solid forms is called a precipitation reaction. Solid = precipitate

A reaction in which a solid forms is called a precipitation reaction. Solid = precipitate Chapter 7 Reactions in Aqueous Solutions 1 Section 7.1 Predicting Whether a Reaction Will Occur Four Driving Forces Favor Chemical Change 1. Formation of a solid 2. Formation of water 3. Transfer of electrons