Equilibrium and Stress Edward A. Mottel Department of Chemistry Rose-Hulman Institute of Technology

Resources Available  Exp. C: Equilibrium

Observations Fe(NO 3 ) 3 NH 4 SCN KSCN NaNO 3 H 2 SO 4 CuSO 4 Co(NO 3 ) 2 Each compound breaks into one type of positive ion (cation) and one type of negative ion. What ions are formed? What color was observed for each compound?

Observations NO 3 - SCN - SO 4 2- Fe 3+ colorless NH 4 + colorless K+K+ Na + colorless H+H+ Cu 2+ blue Co 2+ pink Which ions are responsible for color?

Concentration Effects Thiocyanatoiron(III) Ion System

Write a balanced molecular equation for this reaction.molecular equation Write a balanced ionic equation for this reaction.ionic equation Write a balanced net ionic equation for this reaction.net ionic equation

Molecular Equation Fe(NO 3 ) 3 + NH 4 SCNNH 4 NO 3 + FeSCN(NO 3 ) 2

Ionic Equation Fe 3+ (aq)+ 3 NO 3 - (aq)+ SCN - (aq) [FeSCN] 2+ + NH 4 + (aq) + NO 3 - (aq)+ NH 4 + (aq) Complex ions are sometimes written in brackets without phase annotation. thiocyanatoiron(III) ion Break each compound into one cation and one anion. 3

Net Ionic Equation Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+ Cancel identical ions on both sides of the equation. Fe 3+ (aq)+ 3 NO 3 - (aq)+ SCN - (aq) [FeSCN] 2+ + NH 4 + (aq) + 3 NO 3 - (aq)+ NH 4 + (aq)

What species is responsible for the red color?

[reactants] [products] Thiocyanatoiron(III) Ion Equilibrium Mass-Action Expression Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] Write the mass-action expression for the formation of the thiocyanatoiron(III) ion. Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

+ Fe(NO 3 ) 3 What does a darker red color indicate? Why does the solution turn a darker red color? [reactants] [products] Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] = K ? What ions are added when Fe(NO 3 ) 3 is added to the solution? Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

+ KSCN Why does the solution turn a darker red color? [reactants] [products] Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] = K ? What ions are added when KSCN is added to the solution? Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

+ NH 4 SCN Why does the solution turn a darker red color? [reactants] [products] Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] = K ? Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

+ EDTA Why does the solution turn a lighter red color? [reactants] [products] Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] Fe 3+ (aq)+ EDTA(aq)[FeEDTA] H + (aq) Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

+ water Why does the solution turn a lighter red color? [reactants] [products] Q = [Fe 3+ ][SCN - ] [ [FeSCN] 2+ ] Does the equilibrium shift? Fe 3+ (aq)+ SCN - (aq)[FeSCN] 2+

Pressure Effects Nitrogen Dioxide-Dinitrogen Tetroxide System

Nitrogen Dioxide - Dinitrogen Tetroxide NO 2 (g)+ NO 2 (g)N 2 O 4 (g) N O O N O O N O O N O O

Nitrogen Dioxide - Dinitrogen Tetroxide 0 sec1 sec10 sec NO 2 (g)+ NO 2 (g)N 2 O 4 (g)

[reactants] [products] Nitrogen Dioxide - Dinitrogen Tetroxide Mass-Action Expression Q = Why does the gas initially get darker and then lighten? P NO 2 ( )2)2 P N2O4N2O4 NO 2 (g)+ NO 2 (g)N 2 O 4 (g)

Dilution Effects Tetrachlorocuprate(II) Ion

Which ion is responsible for the color in each solution? Cu 2+ (aq)+ 4 Cl - (aq)[CuCl 4 ] 2-

Tetrachlorocuprate(II) Ion and Water Deionized water causes the pale blue color, salt water gives a pale green solution. top view Cu 2+ (aq)+ 4 Cl - (aq)[CuCl 4 ] 2-

Tetrachlorocuprate(II) Ion and Water Cu 2+ (aq)+ 4 Cl - (aq)[CuCl 4 ] 2-

[reactants] [products] Tetrachlorocuprate(II) Ion Equilibrium Mass-Action Expression Q = [Cu 2+ ][Cl - ] 4 [ [CuCl 4 ] 2- ] Why does the addition of water change the solution color, but the addition of salt water have no effect? Cu 2+ (aq)+ 4 Cl - (aq)[CuCl 4 ] 2-

Temperature Effects Nitrogen Dioxide-Dinitrogen Tetroxide Tetrachlorocobaltate(II) Ion

Nitrogen Dioxide - Dinitrogen Tetroxide Is the equilibrium reaction endothermic or exothermic? ice water room temp hot water NO 2 (g)+ NO 2 (g)N 2 O 4 (g)

Nitrogen Dioxide - Dinitrogen Tetroxide Mass-Action Expression Q = Why does the color change? P NO 2 ( )2)2 P N2O4N2O4 NO 2 (g)+ NO 2 (g)N 2 O 4 (g)

Tetrachlorocobaltate(II) Ion Which ion is responsible for the blue ion? Co 2+ (aq)+ 4 Cl - (aq)[CoCl 4 ] 2-

Tetrachlorocobaltate(II) Ion Equilibrium Mass-Action Expression K = [Co 2+ ][Cl - ] 4 [ [CoCl 4 ] 2- ] pinkcobalt blue When the solution is heated, is the equilibrium constant increasing or decreasing? Co 2+ (aq)+ 4 Cl - (aq)[CoCl 4 ] 2-

6/24/2015