Introduction
If you have acidic soil it can be neutralized by limestone. The capacity of a liming material to neutralize the soil acidity is expressed as its neutralising value (NV). The higher the NV, the greater the ability of the product to raise soil pH. Calcium and magnesium carbonate are the effective components of limestone. Pure calcium carbonate has NV of 100, which is the standard. Ideally, NV should be over 95.
The value of limestone is in the ability to neutralize soil acidity. However, you may have uneven results when you add limestone, even if you follow the recommended application rates and procedures. Limestone's properties differ considerably, and these difference s influence the limestone's ability to neutralize soil acidity. Effectiveness depends on the purity of the liming material and how finely it is ground. Handling or storage properties, however, do not indicate the quality of liming material and have no functions in soil chemistry and fertility. The purity of lime is rated by a laboratory's measurement of a Calcium Carbonate
Equivalent (CCE). The CCE is written as a weight percentage of the material. CCE also reflects the chemicals present in the limestone (calcium carbonate, magnesium carbonate, calcium hydroxide, etc.). The lower the CCE value, the more lime you will need to neutralize the soil's acidity.
Equipment
AR grade calcium carbonate
Hydrochloric acid – 0.5M standardised
Sodium Hydroxide – 1.0M standardised
Phenolphthalein indicator – 4g of phenolphthalein dissolved in 100ml of methanol (4% w/v)
Distilled water
50 +/- 0.05ml burette
250ml conical flasks and rubber stoppers
50ml pipette
100ml graduated cylinder
Hotplate
Sample drying oven
Sample trays
Analytical balance
Selected limestone samples for the period of analysis.
Safety Equipment
Safety Equipment
Enclosed footwear
Laboratory coat
Safety glasses
Rubber gloves
Method
Part 1. Confirmation of standardisation of solutions using AR grade CaCO3
The determination of neutralising value is sensitive to correctly calibrated reagents. AR grade
CaCO3 is used as a standard prior to testing actual limestone samples to confirm the accuracy of standards used in the procedure.
1. Place approximately 10 grams of calcium carbonate onto a sample tray and dry in the 100
2. Set up the burette in the stand with the clamps, and fill with standardised sodium hydroxide. 3. Accurately weigh approximately 1.00 gram of the dried calcium carbonate into a conical flask and place a stopper on the flask. Weigh out a duplicate sample. Record weights.
4. Pipette 50ml of 0.5M hydrochloric acid into each flask and re-stopper lightly.
5. Bring the flasks to boiling on the hotplate and then simmer for 10 minutes.
6. Add 50ml of distilled water to each along with 3 drops of phenolphthalein indicator.
7. Titrate each with 1.0M sodium hydroxide from the burette, with the end point occurring as the solution changes from clear to purple. Record the titre.
8. Calculate the neutralising value for calcium carbonate.
Part 2. Testing of delivered limestone samples
1. Place the pulverised limestone sample into a sample tray and place into drying oven at
100oC for a maximum of 1 hour.
3. Accurately weigh approximately one gram of the dried limestone into a conical flask and place a stopper on the flask. Weigh out a duplicate sample. Record weights.
4. Pipette 50ml of 0.5M hydrochloric acid into each flask and re-stopper lightly.
5. Bring the flasks to boiling on the hotplate and then simmer for 10 minutes.
6. Add 50ml of distilled water to each
