Yuting Chen

Yuting Chen

he/his

Visiting Assistant Professor

Fire Katana

Procedure

  1. Place 50g calcium carbonate in a beaker with stir bar, add 1 mol acetic acid
    • The calcium carbonate can be reagent grade, or from eggshells/chalk. You will have to filter out the other solids before evaporating if not using a reagent
    • The acetic acid can be glacial (~57mL, dilute to ~400mL) or from vinegar (~1.2L for 5% by mass vinegar)
  2. Continue stirring until carbon dioxide bubbles stop forming
  3. Heat the solution to ~80–90 °C to evaporate the water off
  4. Remove from heat before it burns and transfer to a watch glass to finish drying
  5. Measure 15 g of dried calcium acetate, dissolve in 50 mL water
  6. Slowly add the calcium acetate solution to 150 mL ethanol while stirring slowly with a glass stir rod. The calcium acetate should crash out of solution
  7. Take the gel, apply it to the sheath of the sword, and light on fire!

Chemistry

\[\mathrm{CaCO_3 (s) + 2 \, CH_3COOH (aq) \longrightarrow Ca(CH_3COO)_2 (aq) + H_2O (l) + CO_2 (g)}\]

The reaction of calcium carbonate \(\left(\mathrm{CaCO_3 }\right)\) with acetic acid \(\left(\mathrm{CH_3COOH }\right)\) produces calcium acetate \(\left(\mathrm{Ca(CH_3COO)_2 }\right)\), water \(\left(\mathrm{H_2O }\right)\), and carbon dioxide \(\left(\mathrm{CO_2 }\right)\).

We stop the reaction once the carbon dioxide stop since that indicates the reaction is complete. Water is a product that needs to be evaporated off to get solid calcium acetate. This is why the glacial form of acetic acid is preferred since there is less water from the vinegar to evaporate off.

Calcium acetate is highly soluble in water, with a room temperature solubility of \(34.7 \, \mathrm{g}/100 \, \mathrm{mL}\), so at \(15 \, \mathrm{g}/50 \, \mathrm{mL}\) we are nearly fully saturated. Ethanol is a less polar than water due to less hydrogen bonding, so calcium acetate, an ionic compound, is more soluble in the moree polar water than the comparatively less polar ethanol. Like dissolves like!

With the lower solubility, the mixture becomes supersaturated, which means the solution cannot hold any more solute, and the calcium acetate precipitates out as a gel.

Pictures