CALCIUM CARBONATE EQUIVALENT

Acid neutralization
Reagents and Apparatus
1 N HCl standardized
1 N NaOH, standardized and protected from air
Phenolphthalein indicator solution
50 ml burette
25 and 10 ml pipettes
250 ml Erlenmeyer flasks with small watchglasses

Procedure
1. Weigh out two 5g samples of soil on top-loading balance and record to nearest hundredth of a gram, i.e. 5.00g. Use 2 grams if soil is known to be high in carbonates, 1g for limestone samples.
2. Transfer the samples to 250mL Erlenmeyer flasks.
3. With a pipette, add 25mL of previously standardized 1N HCl.
4. Heat on a steam hot plate for 30 minutes. Cover with small watchglass to minimize HCl loss.
5. Add approximately 100mL of distilled water.
6. Heat to boiling and cool slightly.
7. Add 3 drops of phenolphthalein indicator and titrate to a faint pink endpoint with previously standardized 1N NaOH.
8. Calculate the percent CaCO3 equivalent.

Remarks (correspond to procedure number)
1. It is a good idea to check this determination by doing it in duplicate.
2. 1g of pure CaCO3 would require 20meq of acid for neutralization. Ca(OH)2 or CaO will require more.
3. All reactive material should be neutralized in this time.
4. The water is added merely to bring the solution to a convenient volume for titration.
5. The solution is heated to drive off CO2 which would give an erroneous endpoint.
6. The pink color should persist 30 seconds at the endpoint after thorough swirling of the sample.

Calculations
1. (mL HCl added * N HCl) – (mL NaOH added * N NaOH) = meq HCl neutralized
2. meq HCl neutralized * 100 = percent CaCO3 equivalent
          20 meq/g CaCO3 * wt of soil