[Chem 16.1] LE 1

Copper Series (1st Reaction)

Cu(NO₃)_{2 (aq)} + 2NaOH_(aq) —> Cu(OH)_2(s) + 2NaNO_3(aq)

Copper Series (2nd Reaction)

Cu(OH)_2(s) —> ∆ CuO_(s) + H₂O_(l)

Copper Series (3rd Reaction)

CuO(s) + H₂SO_4(aq) —> CuSO_4(aq) + H₂O_(l)

Copper Series (4th Reaction)

CuSO_4(aq) + Zn_(s) —> Cu_(s) + ZnSO_4(aq)

Copper Series (5th Reaction)

2Cu_(s) + O_2(g) —> ∆ 2CuO_(s)

In recrystallization, solute must be?

1. Highly soluble at high temperature

2. Sparingly soluble at low temperature

3. No chemical reaction with solvent

4. Moderately volatile (evaporates easily)

5. Cheap, non-toxic, non-flammable

6. Melting point of solute > Boiling point of solvent

In recrystallization, insoluble impurities are removed by _____

hot filtration

In recrystallization, soluble impurities are removed by _____

cold filtration

In recrystallization, colored impurities are removed by _____ through _____

activated charcoal, adsorption

During hot filtration, we use _____ filter paper to collect the _____

fluted, filtrate

During hot filtration, slow filtration leads to _____

premature crystallization

During hot filtration, slow cooling promotes formation of _____ crystals

large and pure

What are some crystallization issues?

1. Supersaturated solution —> No crystals form

   • Fix: Seeding (Introduce nucleation site)

2. Unsaturated solution —> Too much solvent

   • Fix: Boil off excess solvent

Recrystallization generally leads to _____ yield and _____ purity crystals

higher, lower

In sublimation, solute must be?

Vapor pressure > Boling point

Sublimation generally leads to _____ yield and _____ purity crystals

lower, higher

What range is considered pure?

0.5-1.5°C

What is the melting point of benzoic acid?

122.3°C

Activity Series of Non-metals

Cl₂ > Br₂ > I₂

In the NH₃ test, a light blue complex means the reaction is _____ and a colorless complex means the reaction is _____

incomplete, complete

In the copper cycle, the addition of HCL removes _____

excess zinc

Contaminants present, higher or lower yield?

Higher

Zn not removed, higher or lower yield?

Higher

Not enough HCl, higher or lower yield?

Higher

Excess reagents, higher or lower yield?

Higher

Sample loss (bumping or decanting), higher or lower yield?

Lower

Not basic solution, higher or lower yield?

Lower

Insufficient reagents, higher or lower yield?

Lower

Poor transfer (filter paper issue), higher or lower yield?

Lower

• Solution of known concentration

• Delivered from the burette

Titrant

• Solution of unknown concentration

• Found in the Erlenmeyer flask

Analyte

Point where moles of titrant = moles of analyte

Equivalence Point

• Point where indicator changes color

• Experimental approximation of equivalence point

Endpoint

Substance used to accurately determine concentration of a solution

Primary Standard

A primary standard must be?

1. High purity

2. High molar mass

3. Stable in air

4. Straightforward stoichiometry

Substance that changes color near the endpoint

Color Indicator

How does phenolphthalein change color?

Colorless (acidic) —> Pink (basic)

Incomplete dissolution of KHP, effect?

Lower NaOH standardization

Undershooting endpoint, effect?

Higher molarity

Incorrect indicator usage, effect?

Endpoint not visible

Air bubbles in burette, effect?

Lower molarity

Not mixing solution properly, effect?

False endpoint, higher molarity

Temperature changes, effect?

Affects color change timing

Pipetting errors, effect?

Affects molarity

Evaporation of solution, effect?

Higher molarity

Addition of NaOH

• Cu²⁺: Blue ppt.

• Fe³⁺: Brown ppt.

• Ca²⁺: White ppt.

• Zn²⁺: White ppt.

• NH₄⁺: NVR

Addition of Excess NaOH

Zn²⁺: Ppt. dissolved

Addition of NH₃

• Cu²⁺: Blue ppt.

• Fe³⁺: Brown ppt.

• Ca²⁺: NVR

• Zn²⁺: White ppt.

• NH₄⁺: NVR

Addition of Excess NH₃

• Cu²⁺: Ppt. dissolved; Deep blue solution

• Zn²⁺: Ppt. dissolved; Colorless solution

Confirmatory Test for Cu²⁺

Deep blue solution with excess NH₃

Confirmatory Test for Fe³⁺

• KSCN —> Blood red solution

• K₄Fe(CN)₆ —> Dark blue ppt.

Confirmatory Test for Ca²⁺

(NH₄)₂C₂O₄ —> White ppt.

Confirmatory Test for Zn²⁺

• K₃Fe(CN)₆ —> Yellow ppt.

• K₄Fe(CN)₆ —> White ppt.

Confirmatory Test for NH₄⁺

NaOH: Red litmus paper turns to blue

Addition of Ba(NO₃)₂

• CO₃^2-: White ppt.

• SO₄^2-: White ppt.

• PO₄^3-: White ppt.

Addition of Fe(NO₃)₃ and Toluene

	Tol. Layer	Aq. Layer
I-	Pink	Orange
SCN-	Colorless	Blood Red
Br-	Colorless	Yellow
NO3-	Colorless	Yellow

Addition of KMnO₄ and Toluene

	Tol. Layer	Aq. Layer
I-	Pink	Yellow
SCN-	Colorless	Colorless/ Peach
Br-	Yellow	Yellow
NO3-	Colorless	Purple

Confirmatory Test for CO₃^2-

CH₃COOH: Ppt. dissolves with bubbling

Confirmatory Test for PO₄^3-

• CH₃COOH: Ppt. dissolves without bubbling

• MgCl₂ —> White ppt.

Confirmatory Test for SO₄^2-

CH₃COOH: Ppt. remains undissolved

Confirmatory Test for I^-

Pink/pinkish-red toluene layer with Fe(NO₃)₃

Confirmatory Test for SCN^-

Deep red solution with Fe(NO₃)₃

Confirmatory Test for Br^-

Yellow/orange toluene layer with KMnO₄

Confirmatory Test for NO₃^-

H₂SO₄: Formation of brown ring