Experiment 7

Part BANDAYA, Francis Charles G.

GERON, Erwin Gerard P.

Theoretical Framework

• HETEROGENOUS EQUILIBRIUM REACTIONS– Type of reversible reaction wherein the reactants

and products are in different phases

• PRECIPITATION REACTION– Soluble ions from different solutions are mixed

forming an insoluble compound called the precipitate

Theoretical Framework

• CENTRIFUGATION– Procedure done to make the precipitate settle at

the bottom of the test tube rapidly by the use of a centrifuge

Theoretical Framework

• Ksp – solubility-product constant

• Qsp – reaction quotient– Using these two values, we can determine

whether a known set of concentrations, when mixed together, will produce a precipitate or not.

– Qsp > Ksp --- backward shift

– Qsp = Ksp --- no shift / equilibrium

– Qsp < Ksp --- forward shift

EXPERIMENTAL DATA

IA. TT A(Pb(NO3)2 TT B (AgNO3)

-10 drops 0.1M -10 drops 0.1M

1. Add HCl dropwise 2. Centrifuge * and decant3. Wash with 5 drops H2O

4. Add 2mL H2O then shake

5. Hot water bath*6. Cool to room temperature*

Observations and Explanations

• Reactions:Pb(NO3)2 (aq) + HCl (aq) <-> PbCl2 (s) + HNO3 (aq)

PbCl2 Ksp = 1.6 x 10-5

Ag(NO3)2 (aq) + HCl (aq) <-> AgCl (s) + HNO3 (aq)AgCl Ksp = 1.6 x 10-10

In the first experiment, it was observed that both solutions yielded precipitates of their own. A white-colored precipitate for Pb(NO3)2 and a purple colored precipitate for AgNO3.

When hot water bath was applied to both solutions, the AgNO3 solution stayed the same while the other solution, Pb(NO3)2, had some of its precipitate dissolved.

When it was left to be cooled to room temperature, the precipitate of Pb(NO3)2 returned to its initial amount.

EXPERIMENTAL DATA

IB. TT A(Pb(NO3)2 TT B (AgNO3)

1. Repeat above procedures2. Add 2mL conc. NH4OH*

Observations and Explanations

• ReactionsPbCl2 (s) + 2NH3 (aq) + 2H2O (l) Pb(OH)2 (s) + 2NH4Cl (aq)

Pb(OH)2 Ksp = 1.2 x 10-15

AgCl (s) + 2NH3 (aq) + 2H2O (l) [Ag(NH3)2]+ (aq) + 2 Cl- (aq)

2H20

[Ag(NH3)2]+ (aq) Ksp = 1.7 x 10-7

In addition of NH4OH, precipitate was still present from the solution with Pb(NO3)2 while the precipitate of the other solution, that with AgNO3, was dissolved.

EXPERIMENTAL DATA

II. TT A(Pb(NO3)2 TT B(Ba(NO3)2)

-10 drops 0.1M -10 drops 0.1M

1. Add 3 drops 0.1M K2CrO4

2. Add 3 drops 1M HNO3 *

3. Add 6M NaOH until ppt occurs4. Centrifuge and decant5. Add 15 drops of 6M NaOH *

Observations and Ideas

• ReactionsPb(NO3)2 (aq) + K2CrO4 (aq) <->PbCrO4 (s) + 2KNO3 (aq)

Ba(NO3)2 (aq) + K2CrO4 (aq) <-> BaCrO4 (s) + 2KNO3

(aq)

PbCrO4 (s) + HNO3(aq) <-> Pb(NO3)2(aq) + H2CrO4 (aq)

Pb(NO3)2 (aq) + 2NaOH (aq) <-> Pb(OH)2 (s) +2NaNO3 (aq)

Ba(NO3)2(aq) + NaOH (aq) <-> Ba(OH)2(s) +NaNO (aq)

When 3 drops each of 0.1 M potassium chromate and 1 M of nitric acid was added to both test tubes, it was observed that the solution with Pb(NO3)2 turned to a cloudy yellow solution and forming a yellow-orange precipitate. On the other hand, the solution containing Ba(NO3)2 turned into a clear orange solution without any sign of precipitate formation

When 3 drops of 6 M NaOH was added to the given solutions, the given solutions were neutralized. The solution with Pb(NO3)2 yielded a yellow-orange precipitate in a clear yellow solution. While the solution with Ba(N03)2 yielded a white precipitate making the solution cloudy and dull.

EXPERIMENTAL DATA

III. TT A TT B-10 dps 0.1M Ba(NO3)2 -10 dps 0.1M Ba(NO3)2

-Add 0.1M NA2CO3 until -Add 0.1M NA2SO4

ppt is complete

1. Centrifuge *2. Decant3. Add 5 drops conc. HCl to

each *

Reactions:Ba(NO3)2(aq) + Na2CO3(aq) <-> BaCO3 (s) + 2NaNO3 (aq)

Ba(NO3)2(aq) + Na2SO4(aq) <-> 2NaNO3 (aq) +BaSO4(s)

When the reagents were added accordingly, both test tubes initially contained colorless solutions. After a while, white precipitate formed making the solution cloudy. After centrifugation, the test tube containing Na2CO3 became clearer than the other.

After adding HCl, the precipitate of test tube A, BaCO3, completely dissolved thus making a clear solution. Effervescence was also observed in the process. On the other hand, the precipitate of test tube B, BaSO4, became less cloudy. The precipitate did not completely dissolve.

EXPERIMENTAL DATA

IV. TT A TT B-10 dps 0.1M Cu(NO3)2 -10 dps 0.1M Cu(NO3)2

1. Add HOAc until acidic to litmus2. Add thioacetamide solution until ppt is

complete3. Centrifuge and decant4. Add 2mL distilled H2O

5. Stir, centrifuge, decant6. A - Add 5 drops 6M HCl

B - Add 5 drops 6M HNO3 *

• Reactions

Cu(NO3)2 (aq) + CH3 CSNH2 (aq) <-> CuS(s)

CuS(s) <-> Cu2+ (aq) + S2-

3CuS(s) + 8H+ 2NO3- (aqueous) <-> 3Cu2+ (aq) + 4H2O (l) + 2NO (g) + 3S (s)

The solution in this experiment is a clear orange liquid with visible precipitate. It was also observed that very few precipitate was left after decantation.

After the addition of HCl and HNO3 to their respective solutions, it was observed that all of the precipitate in the solution with added HCl was dissolved while on the other test tube, the precipitate did not completely dissolve.

Precipitate ka ba?

KSP ka eh! EPAL!