1

E1 Precipitation and Water Purity

“E1 is a onesession lab!”

“Will we do the entireexperiment?”

Experiment 1 Pre-lab Report

Reminder: Pre-lab Report (page 34) is dueat the start of Lab (8am or 11am or 2pm)

Pre-lab Correction Question 1, Part 3)Substitute lead ions for chloride ions:Circle the reference blank test reagent combination thatcould be used to directly verify if precipitate formationinvolves chloride ions ↑ lead

Goals for Experiment 1

One session three hour lab Complete Parts 1 and 2A and 2B (all). Complete part 3 OR 4 as assigned*. Complete team report and turn in at the end

of lab or by the grace period deadlineindicated in the lab manual, p. 232.

* Team assignments are on p. 227

Discussion: first hour of next session Prepare discussion abstract and presentationduring lab or before next session.

Ionic compounds with cations (+ ions)and anions (- ions).

“I’m a cation.Note my eyes!”

Background: Salts

Background: Salts

In the solid, the salt ionsare fixed in position in arigid lattice.

The simplest ratio of the + and - ions in thesolid is represented by the formula of the saltwhere the total charge is neutral (zero).

NaCl

Cr+3 O-2

Formula ?

= Cr2O3

Salt Formulas

2

+ 1 1

1A

+3

+4

+5

+6

18 VIIIA

1 H

1s1

+2 2

IIA

+1 13

IIIA

+2 14

IVA

+3 15

VA

+4 16

VIA

17 V I I A

3 Li

2s1

4 Be

2s2

1 1 Na

3s1

1 2 Mg

3s2

3

IIIB

4

IVB

5

VB

6

VIB

7

VIIB

8 VI I IB

9 !

10 VIIIB

11

IB

12

IIB

1 3 Al

3s23p1

1 9 K

4s1

2 0 Ca

4s2

2 1 Sc

4s23d1

2 2 Ti

4s23d2

2 3 V

4s23d3

2 4 Cr

4s13d5

2 5 Mn

4s23d5

2 6 Fe

4s23d6

2 7 Co

4s23d7

2 8 Ni

4s23d8

2 9 Cu

4s13d10

3 0 Zn

4s23d10

3 1 Ga

4s24p1

3 2 Ge

4s24p2

3 7 Rb

5s1

3 8 Sr

5s2

3 9 Y

5s24d12

4 0 Zr

5s24d2

4 1 Nb

5s24d3

4 2 Mo

5s14d5

4 3 Tc

5s23d5

4 4 Ru

5s14d7

4 5 Rh

5s14d8

4 6 Pd

4d10

4 7 Ag

5s14d10

4 8 Cd

5s24d10

4 9 In

5s25p1

5 0 Sn

5s25p2

5 1 Sb

5s25p3

5 5 Cs

6s1

5 6 Ba

6s2

5 7 L a *

6s25d1

7 2 Hf

6s25d2

7 3 Ta

6s25d3

74

W

6s25d4

7 5 Re

6s24d5

7 6 Os

6s25d6

7 7 Ir

5d76s2

7 8 Pt

6s15d9

7 9 Au

6s15d10

8 0 Hg

6s25d10

8 1 Tl

6s26p1

8 2 Pb

6s26p2

83

Bi

6s26p3

8 4 Po

6s26p4

8 7 Fr

7s1

8 8 Ra

7s2

8 9 Ac#

7s26d1

1 0 4 +

7s26d2

1 0 5 +

7s27d3

1 0 6 +

7s26d4

1 0 7 +

7s23d5

1 0 8 +

6s26d6

109 +

6d77s2

+ Element synthesized,

but no official name assigned

Periodic Table with Common Ion Charges

• For common ion chargessee Page 223, Figure 3.

Background: Salt Formulas

In the solid, the salt ionsare fixed in a rigid lattice.

In water solution, saltions are dissociated andfree to move about.

Salt Solubility in Water

Water (H2O) is polar.

Nonpolar versus Polar Solvent

DEMO

Salt Solubility in Polar Solvents

• Polar water molecules reduce the effectivecharges of the ions in the solid salt and thus thesalt ions dissociate and the salt dissolves.

NaCl(s) = Na+(aq) + Cl-(aq)

Seeehttp://www.northland.cc.mn.us/biology/Biology1111/animations/dissolve.html

Salt Solubility

DEMO

• The dissolved salt ions are mobile andcarry a charge in aqueous solution and thusaqueous salt solutions are electrolytes.

3

Precipitation

A solid comes out of solution

Salt solutions before mixing After mixing

+

DEMO

Precipitation

A solid comes out of solution DEMO

1. The positive ion of a dissolved salt combines withthe negative ion from a different dissolved salt.

2. The recombined ions may stay in solution or come out of solution in the form of a solid called a “precipitate”.

Hg2+(aq) + 2 Cl-(aq) + K+(aq) + I-(aq)

HgI2

KCl

Precipitation reactionsPart 1. What is the precipitate?

HgCl2 (aq) + KI (aq) → __?__ (s) clear and colorless salt solutions

_? ppt.

_?__ ↓

REFERENCE BLANK TEST

Test mixture designed to identify reactants andspectators (non-reactants) forming the precipitate.

Test Mixture Omits a species (ion) from the reaction mixture. Substitutes a known SPECTATOR ion such as

Na+ or K+ or NO3- for the omitted ion

Reference Blank Tests� Reaction HgCl2 (aq) + KI (aq) → ? Clear and colorless

Conclusion?

Reference blank testHg(NO3)2 + KI →Clear and colorless

DEMO

Cl- is a spectator ion.

Sameproductproperties

4

Reference Blank Test Design

�HgCl2(aq) + KI (aq) →

Invalid testCuCl2 (aq) + KI (aq) →

• The test produces a different reaction with differentproducts and is therefore invalid.

?

DEMO

Reference Blank Test Design

� KI (aq) + HgCl2 (aq) →

Invalid test

Reference Blank Test Design

�HgCl2 (aq) + KI (aq) → ? colorless solutions

Valid Reference Blank Test produces the identical products or noreaction.

BaCl2 (aq) + AgF (aq) → white (s)?

� 3. Ba(NO3)2 (aq) + AgF (aq) → no reaction

Test Observations1. FeCl3 (aq) + AgF (aq) → green (s)

1. Nothing.2. Ba2+ is a spectator.3. Cl- is a reactant.

Q. What do you know about the white (s)?

2. NaCl (aq) + AgF (aq) → white (s)

Course theme

“There are structure andproperty and PeriodicTable relationships”

Useful web sites are: http://www.merlot.org http://www/davah.com/periodic/

http://www.webelements.com

1A VIIIA

1H

1s1 IIA IIIA IVA VA VIA VIIA

2He1s2

3Li

2s1

4Be

2s2

5B

2s22p1

6C

2s22p2

7N

2s22p3

8O

2s22p4

9F

2s22p5

1 0Ne

2s22p6

1 1Na

3s1

1 2Mg

3s2 IIIB IVB VB VIB VIIB VIIIB ! VIIIB IB IIB

1 3Al

3s23p1

1 4Si

3s23p2

1 5P

3s23p3

1 6S

3s23p4

1 7Cl

3s23p5

1 8Ar

3s23p6

1 9K

4s1

2 0Ca

4s2

2 1Sc

3d14s2

2 2Ti

3d24s2

2 3V

3d34s2

2 4Cr

3d54s1

2 5Mn

3d54s2

2 6Fe

3d64s2

2 7Co

3d74s2

2 8Ni

3d84s2

2 9Cu

3d1 04s1

3 0Zn

3d1 04s2

3 1Ga

4s24p1

3 2Ge

4s24p2

3 3As

4s24p3

3 4Se

4s24p4

3 5Br

4s24p5

3 6Kr

4s24p6

3 7Rb

5s1

3 8Sr

5s2

3 9Y

4d15s2

4 0Zr

4d25s2

4 1Nb

4d35s2

4 2Mo

4d55s1

4 3Tc

4d55s2

4 4Ru

4d75s1

4 5Rh

4d85s1

4 6Pd

4d10

4 7Ag

4d1 05s1

4 8Cd

4d1 05s2

4 9In

5s25p1

5 0Sn

5s25p2

5 1Sb

5s25p3

5 2Te

5s25p4

5 3I

5s25p5

5 4Xe

5s25p6

5 5Cs

6s1

5 6Ba

6s2

5 7

La*

5d16s2

7 2Hf

5d26s2

7 3Ta

5d36s2

7 4W

5d46s2

7 5Re

5d56s2

7 6Os

5d66s2

7 7Ir

5d76s2

7 8Pt

5d96s1

7 9Au

5d1 06s1

8 0Hg

5d1 06s2

8 1Tl

6s26p1

8 2Pb

6s26p2

8 3Bi

6s26p3

8 4Po

6s26p4

8 5At

6s26p5

8 6Rn

6s26p6

8 7Fr

7s1

8 8Ra

7s2

8 9Ac#

6d17s2

1 0 4 +

6d27s2

1 0 5 +

6d37s2

1 0 6 +

6d47s2

1 0 7 +

6d57s2

1 0 8 +

6d67s2

1 0 9 +

6d77s2

+ Element synthesized,

but no official name assigned

Periodic Trends• Look for patterns within families (columns)• Look for patterns across groups of families (pre-transition, transition, post-transition)

5

Part 2A. Precipitation Studies

Discussion questions, p. 48 Is the solubility of a salt predictable from theposition of its cation’s element in the PeriodicTable?

Is there a relationship between cation chargeand precipitation? Compare ….

Hypothesis Formation Formulate your hypothesis and predictions based

on Periodic Table information and provided models. Consider cation size (ionic radii) and charge

Example: Solubility of MgF2 (s) versus BaF2(s)?

Hypothesis Formation

Polar water molecules reduce the effective charges of theions in the solid and provide a hydration shield around eachdissolved ion.

Example: Predict the solubility of NaF (s) versus FeF3(s)

Figure: Water Molecules oriented about Ions

SO42-S2-C2O4

2-I- CrO42-Cl-Cations

Part 2A Table, page 23; Team cation assignments, page 227

Hg2+

Nitrate salts Precipitating Agent Anions (Sodium salts)

Part 2B. Can I identify it?

Identify an unknown metal ion based onprecipitation observations from part 2A:

Caution: Save your acetate sheet results fromPart 2A for use in Part 2B

Discussion Preparation

You will NOT get points for justreproducing the class data.

• Collect the collated class data• Manipulate the class data

6

Part 3. Concentration and Precipitation

1. Does the amount of ppt. remain the same orincrease or decrease at different concentrationsof reacting salts?

2. Filter the product mixture obtained at differentconcentrations. Test the filtrate to determine,does the filtrate contain unprecipitated ions?

• Examine the impact of concentration on precipitation.

Background: Concentration and Precipitation

Saturated solution = contains the maximumamount of solute (e.g., salt) that can be dissolved ina given solution volume.

Concentration and Precipitation

• Precipitation occurs only if concentration ofthe salt exceeds saturation (solubility limits)

DEMO

0.10 M KI(aq)+ 0.10 M HgCl2 (aq) →

10-3 M KI(aq) + 10- 4 M HgCl2 (aq) →

ppt.

NO ppt.

Concentration and Precipitation

DEMOSupersaturation

• The separation of a solid (e.g., aprecipitate) from a liquid

Background: Filtration

DEMO

• Precipitation reactions are equilibrium systems• There are both reactants (I.e., unprecipitated

reactant ions) and products (i.e., the precipitate)present in any equilibrium system

Concentration and Precipitation

DEMO1. Remove the ppt. by filtration2. Filtrate: Check for presenceof unprecipitated reactant ions.

7

Part 4. Solvent Pollution and Precipitation

• Investigate the impact of different solvents (water,acetone, and hexane) on salt solubility andprecipitation.

Discussion (Question 5, page 48)• What is the relationship, if any, between saltsolubility, precipitation, and solvent polarity?

Part 4 Non-Aqueous Solvents

HEXANE (C6H14) is nonpolar

ACETONE (CH3COCH3) is moderately polar. O

C

/ \ CH3 CH3

CH3CH2CH2CH2CH2CH3

Background: Solvent Polarity and Solubility

Polar and non-polar solvents are immiscible

Different polar solvents are miscible

DEMO

Salt solubility and solvent polarity

Acetone is added to a saturatedsolution of CuSO4(aq)

DEMO

Q1. Does the solubility of CuSO4 Increase? Decrease? Remain the same?Q2. What will you observe?

Solvent Polarity and Solubility

The less polar the polar solvent environment, thelower the solubility of the salt.

Questions?Contact nkerner@umich.edu