Alum Synthesis Lab Review

Flashcards for the Alum Synthesis Lab

Synthesis of Alum

Involves a redox reaction and the formation of a complex ion.

Experimental Objective (Alum Synthesis)

Synthesize Alum from aluminum, potassium hydroxide, and sulfuric acid in water in 2 steps; determine % yield of solid alum from initial input of aluminum.

Reaction 1: Aluminum with KOH (dissolution)

2 Al(s) + 2 KOH(aq) + 6 H2O(1) → 2 KAl(OH)4 (aq) + 3 H2(g)

Reaction 2: Sulfuric Acid Addition (precipitation of Al(OH)3)

2 KAl(OH)4(aq) + H2SO4 (aq) → 2 Al(OH)3 (s) + K2SO4 (aq) + 2 H2O(1)

Reaction 3: Further Sulfuric Acid Addition (dissolving of Al(OH)3)

2Al(OH)3 (s) + H2SO4 (aq) → Al2(SO4)3 (aq) + 6 H2O(1)

Reaction 4: Alum Precipitation on Cooling

K2SO4 (aq) + Al2(SO4)3 (aq) + 24 H2O(1) → 2 KAl(SO4)2·12 H2O(s)

Overall Net Ionic Equation

K(+aq) + Al(3+aq) + 2 SO4(2–aq) +12 H2O(l) → KAl(SO4)2·12 H2O(l)

Multi-step reactions

Products of first reaction become reactants in second reaction

Reaction of Aluminum with KOH and Water

2Al(s) + 2K+(aq) + 2OH-(aq) + 6H2O(l) à 2[Al(OH)4]-(aq) + 2K+(aq) + 3H2(g)

Oxidation Half Reaction

2Al(s) + 8OH-(aq) + 6H2O(l) à 2[Al(OH)4]-(aq) + 6e-

Reduction Half Reaction

6H2O(l) + 6e- à 3H2(g) + 6OH-(aq)

Aluminum hydroxide precipitation

H+(aq) + [Al(OH)4]-(aq) à Al(OH)3(s) + H2O(l)

Hydrated aluminum ions formation

Al(OH)3(s) + 3H2O(l) + 3H+(aq) à [Al(H2O)6]3+(aq)

Alum Formation

K+(aq) + 6H2O(l) + 2SO42-(aq) + [Al(H2O)6]3+(aq)à KAl(SO4)2.12H2O(s)

Aluminum dissolution

Dissolution of aluminum in potassium hydroxide (KOH) solution produces potassium aluminate and hydrogen gas.

Alum Uses - Chemical

Tanning leather, mordant for dyes, clarifying turbid liquids.

Alum Uses - Medicinal

Astringent/styptic, antiseptic, natural deodorant, aftershave.

Alum Uses - Culinary

Additive to baking powder.

Alum Uses - Traditional

Ayurveda (phitkari/saurashtri), Traditional Chinese Medicine (ming fan).

White Alum Health Benefits

Skin tightening, wrinkles, dark underarms, dandruff, hair removal, lice, cracked heels.

Red Alum Health Benefits

Mouthwash, muscle cramps, bleeding cuts, pimples, dysentery, body odor, diarrhea.

Acetic Acid, Glacial (CH3COOH) Molarity

17.4 M

Ammonium Hydroxide (NH4OH) Molarity

14.8 M

Hydrochloric Acid (HCl) Molarity

12.1 M

Nitric Acid (HNO3) Molarity

15.8 M

Phosphoric Acid (H3PO4) Molarity

14.7 M

Potassium Hydroxide (KOH) Molarity

11.7 M

Sodium Hydroxide (NaOH) Molarity

19.1 M

Molarity Calculation - Step 1

Determine the mass of solution by multiplying the volume of the solution by the density of the solution using the formula: mass = volume x density

Molarity Calculation - Step 2

Determine concentration in percent by mass of the solute in solution and change to the decimal equivalent.

Molarity Calculation - Step 3

Calculate the molar mass of the compound, MM.

Molarity Calculation - Step 4

Multiply mass (step 1) by mass % (step 2) and divide by molecular mass (step 3) to find the number of moles present in the whole solution.

Molarity Calculation - Step 5

Divide the number of moles (step 4) by the volume in liters of the solution to find the molarity of the solution.

Percentage Yield Formula

%age yield = (W2/ W3) x 100 where W2 is the mass of alum obtained and W3 is the theoretical yield

Molar Mass of Aluminum

26.98g/mol

Molar Mass of KAl(SO4)2.12H2O

474.21g/mol