AP Chemistry Unit 3: Presentation C Precipitation Reactions - - PDF document

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Unit 3: Presentation C Precipitation Reactions

AP Chemistry Slide 2 / 20 Types of Chemical Reactions Seashells are created by the precipitation reaction below. Ca2+(aq) + CO32-(aq) --> CaCO3(s) Slide 3 / 20

Types of Reactions

Chemical reactions are classified by what process is occurring by means of the reaction.

Type What is occurring Example Precipitation formation of solid from mixing of two aqueous solution

Co2+(aq) + 2OH-(aq) --> Co(OH)2(s)

Acid/Base exchange of H+ ions NH4+(aq) + OH-(aq) --> NH3(aq) + H2O(l) Redox exchange of electrons

Mg(s) + Zn2+(aq) --> Mg2+(aq) + Zn(s)

*Note: There are a few reactions that do not neatly fit into one

• f these categories. They will be dealt with later.

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Precipitation Reactions

In order to predict the products of a precipitation reaction, we must know which ions tend to be soluble in water and which ones tend not to be soluble. Always soluble Soluble unless with Ag+, Hg+,

• r Pb2+

Soluble unless with Ag+, Hg+, Pb2+, Ca2+, Sr2+, Ba2+ Insoluble unless paired with ion that always dissolves acetate nitrate nitrite ammonium alkali metal ions chlorate bicarbonate chloride bromide iodide sulfate hydroxide phosphate carbonate sulfide flouride sulfite chromate

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When writing a precipitation reaction, a few simple steps must be followed. Example: If aqueous solutions of potassium hydroxide and barium nitrate are mixed... Picture what ions are present K+(aq) + OH-(aq) + Ba2+(aq) + NO3-(aq) Decide which ions will form a ppt. and show the reaction of these ions only in the formation of the ppt. product K+(aq) + OH-(aq) + Ba2+(aq) + NO3-(aq) 2OH-(aq) + Ba2+(aq) --> Ba(OH)2(s) Note: Ions not involved in the reaction are known as spectator ions. The spectator ions here are K+(aq) and NO3-(aq).

Precipitation Reactions

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1 What would be the product(s) of mixing aqueous solutions of silver nitrate and sodium phosphate? A AgNO3(s) B Ag3PO4(s) and NaNO3(s) C NaNO3(s) D Ag3PO4(aq) E Ag3PO4(aq) and NaNO3(aq)

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1 What would be the product(s) of mixing aqueous solutions of silver nitrate and sodium phosphate? A AgNO3(s) B Ag3PO4(s) and NaNO3(s) C NaNO3(s) D Ag3PO4(aq) E Ag3PO4(aq) and NaNO3(aq)

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Answer D

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2 If aqueous mixtures of ammonium fluoride and calcium nitrate are mixed, which two ions would be spectator ions? A Ca2+ and NO3- B Ca2+ and NH4+ C NH4+ and NO3- D NH4+ and Ca2+ E Ca2+ and F-

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2 If aqueous mixtures of ammonium fluoride and calcium nitrate are mixed, which two ions would be spectator ions? A Ca2+ and NO3- B Ca2+ and NH4+ C NH4+ and NO3- D NH4+ and Ca2+ E Ca2+ and F-

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Answer C

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3 Which of the following aqueous solutions would form a precipitate if mixed with an solution of strontium chloride? A I only B II only C III only D I and III only E II and III only

• I. AgNO3(aq)
• II. Ca(NO3)2(aq)
• III. NaOH(aq)

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3 Which of the following aqueous solutions would form a precipitate if mixed with an solution of strontium chloride? A I only B II only C III only D I and III only E II and III only

• I. AgNO3(aq)
• II. Ca(NO3)2(aq)
• III. NaOH(aq)

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Answer D

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4 Which of the following would be the correct reaction when aqueous solutions of lead(II)acetate and magnesium sulfate are mixed? A Pb2+(aq) + SO42-(aq) --> PbSO4(s) B Mg2+(aq) + Pb2+(aq) --> PbMg(s) C Mg2+(aq) + C2H3O2-(aq) --> Mg(C2H3O2)2(s) D Pb2+(aq) + SO42-(aq) + Mg2+(aq) + C2H3O2-(aq) --> PbSO4(s)

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4 Which of the following would be the correct reaction when aqueous solutions of lead(II)acetate and magnesium sulfate are mixed? A Pb2+(aq) + SO42-(aq) --> PbSO4(s) B Mg2+(aq) + Pb2+(aq) --> PbMg(s) C Mg2+(aq) + C2H3O2-(aq) --> Mg(C2H3O2)2(s) D Pb2+(aq) + SO42-(aq) + Mg2+(aq) + C2H3O2-(aq) --> PbSO4(s)

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Answer A

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5 If aqueous solutions of magnesium iodide are sodium phosphate are mixed and the resulting solution filtered, what ions would be present dissolved in the filtrate? A magnesium ion and phosphate ions B magnesium ion and iodide ion C sodium ion and iodide ion D sodium ion and magnesium ion E sodium ion and phosphate ion

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5 If aqueous solutions of magnesium iodide are sodium phosphate are mixed and the resulting solution filtered, what ions would be present dissolved in the filtrate? A magnesium ion and phosphate ions B magnesium ion and iodide ion C sodium ion and iodide ion D sodium ion and magnesium ion E sodium ion and phosphate ion

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Answer C

Slide 11 (Answer) / 20 Precipitation Reactions

A number of precipitates have signature colors and can be identified by them. Precipitate Color PbI2(s) Yellow AgI(s) Yellow Cu(OH)2(s) Blue Ag2S(s) Black CuO(s) Black PbCrO4(s) Yellow AgBr(s) Cream

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6 Two aqueous solutions are mixed forming a black

• precipitate. Which of the following could be the correct

identity of the two aqueous solutions? A Pb(NO3)2(aq) and AgNO3(aq) B NaI(aq) and AgNO3(aq) C CuNO3(aq) and MgSO4(aq) D AgC2H3O2(aq) and K2S(aq) E Sr(NO3)2(aq) and KOH(aq)

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6 Two aqueous solutions are mixed forming a black

• precipitate. Which of the following could be the correct

identity of the two aqueous solutions? A Pb(NO3)2(aq) and AgNO3(aq) B NaI(aq) and AgNO3(aq) C CuNO3(aq) and MgSO4(aq) D AgC2H3O2(aq) and K2S(aq) E Sr(NO3)2(aq) and KOH(aq)

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Answer D

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7 An aqueous solution "A" will form a yellow precipitate when mixed with aqueous solution "B" and no precipitate at all when mixed with solution "C". What could be the identity of the three solutions? A MgSO4(aq) Pb(NO3)2(aq) NH4F(aq) B NH4I(aq) AgNO3(aq) KF(aq) C AgNO3(aq) NH4I(aq) KF(aq) D NaI(aq) Pb(NO3)2(aq) NH4F(aq)

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7 An aqueous solution "A" will form a yellow precipitate when mixed with aqueous solution "B" and no precipitate at all when mixed with solution "C". What could be the identity of the three solutions? A MgSO4(aq) Pb(NO3)2(aq) NH4F(aq) B NH4I(aq) AgNO3(aq) KF(aq) C AgNO3(aq) NH4I(aq) KF(aq) D NaI(aq) Pb(NO3)2(aq) NH4F(aq)

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Answer B

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The amount of precipitate made and concentration of ions left in solution can be determined using basic stoichiometry. For example: What is the concentration of all ions left in solution after 200 mL of 0.1 M CaBr2(aq) is mixed with 200 mL of 0.2 M Pb(NO3)2(aq)?

Pb2+(aq) + 2Br-(aq) --> PbBr2(s)

0.2 L x 0.1 n/L x 1 = 0.02 mol Ca2+(aq) 0.2 L x 0.1 n/L x 2 = 0.04 mol Br-(aq) 0.2 L x 0.2 n/L x 1 = 0.04 mol Pb2+(aq) 0.2 L x 0.2 n/L x 2 = 0.08 mol NO3-(aq)

Find mole amounts after writing reaction.

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Find concentrations of spectator ions by dividing by total volume after mixing 0.02 mol Ca2+(aq)/0.4 L = 0.050 M 0.08 mol NO3-(aq)/0.4 L = 0.200 M Determine limiting and excess reactants and find concentration of excess ion by dividing by total volume 0.04 mol Pb2+ x 2 mol Br- needed = 0.08 mol Br- needed Only 0.04 mol Br- available so.... Br- - Limits Pb2+ - Excess 0.04 mol Br- x 1/2 mol Pb2+ needed = 0.02 mol Pb2+ needed 0.04 mol Pb2+ - 0.02 mol Pb2+ = 0.02 mol Pb2+/0.4 L =0.050 M

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8 What mass of CaSO4 precipitate can be formed when 50 mL of 0.2 M Ca(NO3)2 mix with 50 mL of 0.3 M Na2SO4? A 0.136 g B 1.36 g C 2.72 g D 2.04 g E 0.204 g

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8 What mass of CaSO4 precipitate can be formed when 50 mL of 0.2 M Ca(NO3)2 mix with 50 mL of 0.3 M Na2SO4? A 0.136 g B 1.36 g C 2.72 g D 2.04 g E 0.204 g

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Answer B

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9 What would be the correct order of ions from highest to lowest concentration in the solution after 300 mL of 0.1 M NH4F is mixed with 700 mL of 0.1 M SrI2(aq)? A F- < Sr2+ < I- < NH4+ B Sr2+ < F- < NH4+ < I- C F- < Sr2+ < NH4+ < I- D NH4+ < F- < Sr2+ < I- E F- < NH4+ < Sr2+ < I-

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9 What would be the correct order of ions from highest to lowest concentration in the solution after 300 mL of 0.1 M NH4F is mixed with 700 mL of 0.1 M SrI2(aq)? A F- < Sr2+ < I- < NH4+ B Sr2+ < F- < NH4+ < I- C F- < Sr2+ < NH4+ < I- D NH4+ < F- < Sr2+ < I- E F- < NH4+ < Sr2+ < I-

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Answer E

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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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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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Answer D

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