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. The calcium carbonate equivalent of the sample :Ls obtained by determining <br /> the amount of unconsumed acid by titration with standardized sodium <br /> hydroxide (Jackson, 1958). <br /> 3.2.3.2 Comments-- <br /> A fizz rating of the neutralization potential is made for each sample to <br /> insure the addition of sufficient acid to react all the calcium carbonate <br /> present. <br /> I <br /> During digestion, do not boil samples. If boiling occurs, discard sample <br /> and rerun. Before titrating with acid, fill buret with acid and drain <br /> completely. Before titrating with base, fill buret with base and dram <br /> completely to assure that free titrant is being added to the sample. <br /> 3.2.3.3 Chemicals-- <br /> 1. Carbon dioxide-free water: Heat distilled water just to boiling in a <br /> beaker. Allow to cool slightly and pour into a container equipped with <br /> ascarite tube. Cool to room temperature before using. <br /> 2. Hydrochloric acid (HC1) solution, 0.1 N, certified grade (Fisher So-A-54 <br /> or equivalent). <br /> 3. Sodium hydroxide (NaOH) , approximately, 0.5 N: Dissolve 20.0 g of NaOH <br /> pellets in carbon dioxide-free water and dilute to 1 liter. Protect from <br /> . 002 in the air with ascarite tube. Standardize solution by placing 50 ml of <br /> certified 0.1 N HCl in a beaker and titrating with the prepared 0.5 N NaOH <br /> until a pH of 7.00 is obtained. Calculate the Normality of the NaOH using <br /> the following equation: <br /> N2 = (NIV1)/V2, where: <br /> Vl = Volume of HCl used. <br /> N1 = Normality of HCl used. <br /> V2 = Volume of NaOH used. <br /> N2 = Calculated Normality of NaOH. <br /> 4. Sodium hydroxide (NaOH) approximately 0.1 N: Dilute 200 ml of 0.5 N <br /> NaOH with carbon dioxide-free water to a volume of 1 liter. Protect from <br /> CO2 in air with ascarite tube. Standardize solution by placing 20 ml of <br /> certified 0.1 N HCl in a beaker and titrating with the prepared 0.1 N NaOH <br /> until a pH of 7.00 is obtained. Calculate the Normality of the NaAH using <br /> the equation in 3.2.3.3 No. 3. <br /> 5. Hydrochloric acid (HC1), approximately 0.5 N: Dilute 42 ml of concen- <br /> trated HCI to a volume of 1 liter with distilled water. Standardize solution _ <br /> by placing 20 ml of the known Normality NaOH prepared in 3.2.3.3 No. 3 in a <br /> beaker and titrating with the prepared HCl until a pH of 7.00 is obtained. <br /> 48 <br />