1 Predicting Chemical Reactions Exchange Reactions (Metathesis Reaction)

2 Precipitation Reactions Predicting Products Consider the reaction between AgNO 3 and NaCl in aqueous solution: AgNO 3 (aq) + NaCl (aq)  AgCl (s) + NaNO 3 (aq) Notice that the anions and cations appear to have exchanged partners.

3 Precipitation Reactions Metathesis Reactions –reactions in which the positive ions and negative ions present in the reactants appear to exchange partners –also called exchange reactions AX + BY  AY + BX AgNO 3 + NaCl  AgCl + NaNO 3

4 Precipitation Reactions How can you predict the products of a reaction between ionic compounds? –Identify the ions (including charge) present in the reactants. –Exchange the anions between the two cations and write the correct formulas (electrically neutral) for the possible products.

5 Precipitation Reactions How can you predict the products of a reaction between ionic compounds? -Determine if any of the products are insoluble in water. If any are insoluble, the reaction will procede! Also, if possible products are in gas form (CO 2 ) or are in the liquid (not aq) form, the reaction will take place. If none of the products are a solid, a gas, or a liquid (i.e. different physical state, physical state other than aq,) there is no reaction….nothing happens. -Write a balanced equation including the physical states of reactants and products.

6 Predicting Reactions Example: Write the chemical equation for the aqueous reaction between Ba(NO 3 ) 2 and Na 2 SO 4. Predict which product(s) will be insoluble. Ions: Ba 2+, NO 3 -, Na +, SO 4 2- At this point, you don’t care how many of each ion you started with.

7 Predicting Reactions Possible Products: Ba 2+ and SO 4 2- BaSO 4 Na + and NO 3 - NaNO 3 Make sure that you combine the ions so that total positive charge = total negative charge

8 Predicting Reactions Determine solubility of possible products: BaSO 4 NaNO 3 Insoluble = solid Soluble = aqueous (s) (aq)

9 Predicting Reactions Write a balanced equation: Ba(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  BaSO 4 (s) + NaNO 3 (aq) You must always make sure that your equation is balanced at this point. unbalanced Ba(NO 3 ) 2 (aq) + Na 2 SO 4 (aq)  BaSO 4 (s) + 2 NaNO 3 (aq) balanced

10 Practice Predict the identity of the precipitate that forms when solutions of Fe 2 (SO 4 ) 3 and LiOH are mixed. Ions present in solution: Fe 3+ SO 4 2- Li + OH -

11 Practice (contd) Write a balanced equation for the reaction: Fe 2 (SO 4 ) 3 (aq)+ LiOH(aq) Fe(OH) 3 (s) + Li 2 SO 4 (aq) Unbalanced!! Fe 2 (SO 4 ) 3 (aq)+ 6 LiOH(aq)2 Fe(OH) 3 (s) + 3 Li 2 SO 4 (aq) Balanced

12 Molecular Equation The molecular equation lists the reactants and products in their molecular form. AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq)

13 Ionic Equation In the ionic equation all strong electrolytes (strong acids, strong bases, and soluble ionic salts) are dissociated into their ions. This more accurately reflects the species that are found in the reaction mixture. Ag + (aq) + NO 3 - (aq) AgNO 3 (aq) + KCl (aq)  AgCl (s) + KNO 3 (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq)

14 Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. Ag + (aq) + NO 3 - (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq) The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Ag + (aq)+ Cl - (aq)AgCl (s)

15 Net Ionic Equation To form the net ionic equation, cross out anything that does not change from the left side of the equation to the right. The only things left in the equation are those things that change (i.e., react) during the course of the reaction. Those things that didn’t change (and were deleted from the net ionic equation) are called spectator ions. Ag + (aq) + NO 3 - (aq) + K + (aq) + Cl - (aq)  AgCl (s) + K + (aq) + NO 3 - (aq)

16 Writing Net Ionic Equations 1.Write a balanced molecular equation. 2.Dissociate all strong electrolytes. 3.Cross out anything that remains unchanged from the left side to the right side of the equation. 4.Write the net ionic equation with the species that remain.

17 Practice Write a net ionic equation for the precipitation reaction that occurs when aqueous solutions of silver nitrate and potassium phosphate are mixed.

18 More practice Lab 8: Write molecular, as well as ionic and net ionic reactions (13 of them) if there is a reaction taking place. Reaction #1: Sodium carbonate plus hydrochloric acid

19 Acids and Bases and Their Reactions

20 Acids Arrhenius defined acids as substances that increase the concentration of H + when dissolved in water. Brønsted and Lowry defined them as proton donors.

21 Acids Increase the H + concentration in water: Example: nitric acid HNO 3 (aq)  H+ (aq) + NO3- (aq)

22 Acids Examples of Acids: –HCl hydrochloric acid –HNO 3 nitric acid –CH 3 COOHacetic acid –H 2 SO 4 sulfuric acid –H 3 PO 4 phosphoric acid Note: Acids can form different numbers of H + ions!

23 Acids Monoprotic acids –have one H in the formula –form a single H + ion when they ionize HNO 3 (aq)  H + (aq) + NO 3 - (aq)

24 Acids Diprotic acids –have two H’s in the formula –can form two H + ion when they ionize completely H 2 SO 4 (aq)  2H + (aq) + SO 4 2- (aq) Polyprotic acids: –Have two or more H’s in the formula –Form two or more H + ions when they ionize completely

25 Bases Arrhenius defined bases as substances that increase the concentration of OH − when dissolved in water. Brønsted and Lowry defined them as proton acceptors.

26 Bases Bases: –substances that accept (react with) H + ions. –any substance that increases the OH - concentration when added to water Examples: –Hydroxide ion (OH - ) OH - (aq) + H + (aq)  H 2 O (l)

27 Bases Examples (cont) –Common hydroxide containing bases: NaOH, KOH, Ca(OH) 2 Note: These are strong electrolytes! NaOH (aq)  Na + (aq) + OH - (aq)

28 Bases Examples (cont): –Ammonia (NH 3 ) Does not contain OH - Accepts H + ion from water and increases the OH - concentration in the water NH 3 (aq) + H 2 O (l) NH 4 + (aq) + OH - (aq) NH 3 is a weak electrolyte!! (double arrow!)

29 Acids & Bases Strong Acid: –an acid that is a strong electrolyte ionizes completely in solution Weak Acid: –an acid that is a weak electrolyte an acid that does not ionize completely

30 Acids & Bases Strong acids: –Know the names and formulas of the 7 common strong acids: HCl (aq)hydrochloric acid HBr (aq)hydrobromic acid HI (aq)hydroiodic acid HClO 3 chloric acid HClO 4 perchloric acid HNO 3 nitric acid H 2 SO 4 sulfuric acid

31 Acids & Bases Examples of Weak Acids HF (aq)hydrofluoric acid H 3 PO 4 phosphoric acid CH 3 COOHacetic acid

32 Acids & Bases Strong Base: –a base that is a strong electrolyte –ionizes completely in solution Weak Base: –a base that is a weak electrolyte –does not ionize completely in solution

33 Acids & Bases Strong Bases: Know the names and formulas of the strong bases –Alkali metal (1A) hydroxides LiOHlithium hydroxide NaOHsodium hydroxide KOHpotassium hydroxide RbOHrubidium hydroxide CsOHcesium hydroxide

34 Acids & Bases Strong bases to know (con’t): –Heavy alkaline earth metal (2A) hydroxides Ca(OH) 2 calcium hydroxide Sr(OH) 2 strontium hydroxide Ba(OH) 2 barium hydroxide

35 Acids & Bases Examples of Weak Bases: ammonia (NH 3 ) sodium bicarbonate (NaHCO 3 ) baking soda a component of Alka-Seltzer

36 Acids + Bases Generally, when solutions of an acid and a base are combined, the products are a salt and water. CH 3 COOH (aq) + NaOH (aq)  CH 3 COONa (aq) + H 2 O (l) Neutralization Reaction

37 Neutralization Reactions When a strong acid reacts with a strong base, the molecular equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l)

38 Neutralization Reactions When a strong acid reacts with a strong base, the ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) H + ( aq ) + Cl - ( aq ) + Na + ( aq ) + OH - ( aq )  Na + ( aq ) + Cl - ( aq ) + H 2 O ( l )

39 Neutralization Reactions When a strong acid reacts with a strong base, the net ionic equation is… HCl (aq) + NaOH (aq)  NaCl (aq) + H 2 O (l) H + (aq) + Cl - (aq) + Na + (aq) + OH - (aq)  Na + (aq) + Cl - (aq) + H 2 O (l) H + ( aq ) + OH - ( aq )  H 2 O ( l )

40 Neutralization Reactions The products of these reactions have very different properties than the reactants. HCl (aq) + NaOH (aq)  H 2 O (l) + NaCl (aq) Sharp sour bitter slippery salt

41 Acid-Base Reactions Salt: –any ionic compound whose cation comes from a base and whose anion comes from an acid –an ionic compound that is neither an acid nor a base In general, acid + metal hydroxide  a salt + water

42 Acid-Base Reactions Neutralization reactions are a type of metathesis reaction. To predict the products: –identify the ions present –exchange anions –write the correct formulas for the products including physical states –write a balanced equation

43 Acid-Base Reactions Example: Write the balanced equation for the reaction between HBr (aq) and Ca(OH) 2 (aq). Ions: H + Br - Ca 2+ OH - Possible Products: H-OH = H 2 O CaBr 2 2HBr (aq) + Ca(OH) 2 (aq)  CaBr 2 (aq) + 2H 2 O (l)

44 Gas-Forming Reactions Some metathesis reactions do not give the product expected. In this reaction, the expected product (H 2 CO 3 ) decomposes to give a gaseous product (CO 2 ) and H 2 O. CaCO 3 (s) + HCl (aq)  CaCl 2 (aq) + CO 2 (g) + H 2 O (l)

45 Gas-Forming Reactions When a carbonate or bicarbonate reacts with an acid, the products are a salt, carbon dioxide, and water. CaCO 3 (s) + HCl (aq)  CaCl 2 (aq) + CO 2 (g) + H 2 O (l) NaHCO 3 (aq) + HBr (aq)  NaBr (aq) + CO 2 (g) + H 2 O (l) “H 2 CO 3 ”

46 Gas-Forming Reactions Similarly, when a sulfite reacts with an acid, the products are a salt, sulfur dioxide, and water. SrSO 3 (s) + 2 HI (aq)  SrI 2 (aq) + SO 2 (g) + H 2 O (l) “H 2 SO 3 ”

47 Gas-Forming Reactions This reaction gives the predicted product, but you had better carry it out in the hood, or you will be very unpopular! But just as in the previous examples, a gas is formed as a product of this reaction. Na 2 S (aq) + H 2 SO 4 (aq)  Na 2 SO 4 (aq) + H 2 S (g)