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What is Alkalinity?

What is Alkalinity? Alkalinity is the measurement of a body of water’s resistance to the lowering of pH when acids are added to the water. Alkalinity Water acquires alkalinity from dissolving rocks (e.g., carbonates)

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What is Alkalinity?

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  1. What is Alkalinity? • Alkalinity is the measurement of a body of water’s resistance to the lowering of pH when acids are added to the water. • Alkalinity • Water acquires alkalinity from dissolving rocks (e.g., carbonates) • Alkalinity influences pH, and thus affects the kinds of aquatic life that will survive in water. • Alkalinity is measured in ppm (mg/L) as CaCO3.

  2. Typical Values • Fresh water typically has alkalinity of 20 - 200 ppm as CaCO3. • Well-buffered waters have alkalinity greater than 100 ppm. The pH should be relatively stable. • Sea water has alkalinity of 100 - 125 ppm as CaCO3.

  3. Sample collection and reporting • Rinse sample bottle 3 times with sample water • Take sample near location of water temperature measurement • Follow kit instructions. Repeat 3 times. • Alkalinity values should agree within the precision of the kit (typically  1 drop of titrant).

  4. Test Kit Procedure • Titration • Ca2CO3 + H+ Ca2+ + HCO3- + H+ H2CO3 + Ca2+ • Indicator • Blue/green + H+ color change (this occurs at pH 4.3)

  5. Quality Control Procedure • Periodically check technique using standard • Track dates of chemical purchase. It is recommended that chemicals be replaced at least once a year; if you are making weekly measurement this will not be a problem because the chemicals in the kit will be used up within a year. • Do not use chemicals past their expiration date.

  6. Baking Soda Standard (2-part dilution) • Step 1 • Weigh 1.9 g of baking soda (NaHCO3). The baking soda should be dry. Add to 500 mL graduated cylinder. • Fill to 500 mL with distilled water and transfer solution to beaker and mix well. • Step 2 • Measure 15 mL of NaHCO3 solution and add to clean 500 mL graduated cylinder • Fill to 500 mL with distilled water • Result • Solution with 70 mg/L as CaCO3 + alkalinity of distilled water (distilled water = approximately 14 mg/L as CaCO3)

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