Slide 1 / 20 Slide 2 / 20 New Jersey Center for Teaching and Learning AP Chemistry Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written Unit 3: Presentation C permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to Precipitation Reactions make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org www.njctl.org Slide 3 / 20 Slide 4 / 20 Types of Chemical Reactions Types of Reactions Chemical reactions are classified by what process is occurring by means of the reaction. What is occurring Type Example formation of solid Precipitation from mixing of two Co 2+ (aq) + 2OH - (aq) --> Co(OH) 2 (s) aqueous solution Acid/Base exchange of H + ions NH 4+ (aq) + OH - (aq) --> NH 3 (aq) + H 2 O(l) Seashells are created by the precipitation reaction below. exchange of Redox Mg(s) + Zn 2+ (aq) --> Mg 2+ (aq) + Zn(s) electrons Ca 2+ (aq) + CO 32- (aq) --> CaCO 3 (s) *Note: There are a few reactions that do not neatly fit into one of these categories. They will be dealt with later. Slide 5 / 20 Slide 6 / 20 Precipitation Reactions Precipitation Reactions When writing a precipitation reaction, a few simple steps must be In order to predict the products of a precipitation reaction, we must followed. know which ions tend to be soluble in water and which ones tend not Example: If aqueous solutions of potassium hydroxide and barium to be soluble. nitrate are mixed... Soluble unless Insoluble unless Soluble unless with Ag + , Hg + , paired with ion Always soluble with Ag + , Hg + , Picture what ions are present Pb 2+ , Ca 2+ , Sr 2+ , that always or Pb 2+ Ba 2+ dissolves K + (aq) + OH - (aq) + Ba 2+ (aq) + NO 3 -(aq) acetate hydroxide nitrate Decide which ions will form a ppt. and show the reaction of phosphate these ions only in the formation of the ppt. product nitrite chloride carbonate K + (aq) + OH - (aq) + Ba 2+ (aq) + NO 3 -(aq) ammonium bromide sulfate sulfide alkali metal ions iodide flouride 2OH - (aq) + Ba 2+ (aq) --> Ba(OH) 2 (s) chlorate sulfite bicarbonate Note: Ions not involved in the reaction are known as spectator ions. chromate The spectator ions here are K + (aq) and NO 3- (aq).
Slide 7 / 20 Slide 8 / 20 1 What would be the product(s) of mixing aqueous 2 If aqueous mixtures of ammonium fluoride and calcium solutions of silver nitrate and sodium phosphate? nitrate are mixed, which two ions would be spectator ions? A AgNO 3 (s) A Ca 2+ and NO 3 - B Ag 3 PO 4 (s) and NaNO 3 (s) B Ca 2+ and NH 4 + C NaNO 3 (s) C NH 4 + and NO 3 - D Ag 3 PO 4 (aq) D NH 4 + and Ca 2+ E Ag 3 PO 4 (aq) and NaNO 3 (aq) E Ca 2+ and F - Slide 9 / 20 Slide 10 / 20 3 Which of the following aqueous solutions would form a 4 Which of the following would be the correct reaction precipitate if mixed with an solution of strontium chloride? when aqueous solutions of lead(II)acetate and magnesium sulfate are mixed? I. AgNO 3 (aq) A I only A Pb 2+ (aq) + SO 42- (aq) --> PbSO 4 (s) II. Ca(NO 3 ) 2 (aq) B II only B Mg 2+ (aq) + Pb 2+ (aq) --> PbMg(s) III. NaOH(aq) C III only C Mg 2+ (aq) + C 2 H 3 O 2 -(aq) --> Mg(C 2 H 3 O 2 ) 2 (s) D I and III only D Pb 2+ (aq) + SO 42- (aq) + Mg 2+ (aq) + C 2 H 3 O 2 -(aq) --> PbSO 4 (s) E II and III only Slide 11 / 20 Slide 12 / 20 Precipitation Reactions 5 If aqueous solutions of magnesium iodide are sodium phosphate are mixed and the resulting solution filtered, A number of precipitates have signature colors and can be what ions would be present dissolved in the filtrate? identified by them. Precipitate Color A magnesium ion and phosphate ions PbI 2 (s) Yellow AgI(s) Yellow B magnesium ion and iodide ion Cu(OH) 2 (s) Blue C sodium ion and iodide ion Ag 2 S(s) Black CuO(s) Black D sodium ion and magnesium ion PbCrO 4 (s) Yellow E sodium ion and phosphate ion AgBr(s) Cream
Slide 13 / 20 Slide 14 / 20 6 Two aqueous solutions are mixed forming a black 7 An aqueous solution "A" will form a yellow precipitate precipitate. Which of the following could be the correct when mixed with aqueous solution "B" and no precipitate identity of the two aqueous solutions? at all when mixed with solution "C". What could be the identity of the three solutions? A Pb(NO 3 ) 2 (aq) and AgNO 3 (aq) A MgSO 4 (aq) Pb(NO 3 ) 2 (aq) NH 4 F(aq) B NaI(aq) and AgNO 3 (aq) B NH 4 I(aq) AgNO 3 (aq) KF(aq) C CuNO 3 (aq) and MgSO 4 (aq) C AgNO 3 (aq) NH 4 I(aq) KF(aq) D AgC 2 H 3 O 2 (aq) and K 2 S(aq) D NaI(aq) Pb(NO 3 ) 2 (aq) NH 4 F(aq) E Sr(NO 3 ) 2 (aq) and KOH(aq) Slide 15 / 20 Slide 16 / 20 Precipitation Reactions Precipitation Reactions The amount of precipitate made and concentration of ions left in Find concentrations of spectator ions by dividing by total volume solution can be determined using basic stoichiometry. after mixing For example: What is the concentration of all ions left in 0.02 mol Ca 2+ (aq)/0.4 L = 0.050 M solution after 200 mL of 0.1 M CaBr 2 (aq) is mixed with 0.08 mol NO 3 -(aq)/0.4 L = 0.200 M 200 mL of 0.2 M Pb(NO 3 ) 2 (aq)? Determine limiting and excess reactants and find concentration of Pb 2+ (aq) + 2Br - (aq) --> PbBr 2 (s) excess ion by dividing by total volume Find mole amounts after writing reaction. 0.04 mol Pb 2+ x 2 mol Br - needed = 0.08 mol Br - needed Only 0.04 mol Br- available so.... Br - - Limits Pb 2+ - Excess 0.2 L x 0.1 n/L x 1 = 0.02 mol Ca 2+ (aq) 0.2 L x 0.1 n/L x 2 = 0.04 mol Br - (aq) 0.04 mol Br - x 1/2 mol Pb 2+ needed = 0.02 mol Pb 2+ needed 0.2 L x 0.2 n/L x 1 = 0.04 mol Pb 2+ (aq) 0.2 L x 0.2 n/L x 2 = 0.08 mol NO 3 -(aq) 0.04 mol Pb 2+ - 0.02 mol Pb 2+ = 0.02 mol Pb 2+ /0.4 L = 0.050 M Slide 17 / 20 Slide 18 / 20 8 What mass of CaSO 4 precipitate can be formed when 50 9 What would be the correct order of ions from highest to mL of 0.2 M Ca(NO 3 ) 2 mix with 50 mL of 0.3 M Na 2 SO 4 ? lowest concentration in the solution after 300 mL of 0.1 M NH 4 F is mixed with 700 mL of 0.1 M SrI 2 (aq)? A 0.136 g A F- < Sr 2+ < I- < NH 4+ B 1.36 g B Sr 2+ < F- < NH 4+ < I- C 2.72 g C F- < Sr 2+ < NH 4+ < I- D 2.04 g D NH 4+ < F- < Sr 2+ < I- E 0.204 g E F- < NH 4+ < Sr 2+ < I-
Slide 19 / 20 Slide 20 / 20 10 How many mL of 0.4 M AgNO 3 solution must be added to 200 mL of 0.4 M NaI in order to form 11.7 grams of AgI precipitate? A 200 mL B 20 mL C 250 mL D 125 mL E 12.5 mL
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