Salinity

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  • Salinity

    1. 1. <ul><ul><li>Salinity is the total amount of dissolved salts in water; grams of salts per kilogram of water (g/kg) or as parts per thousand (ppt). </li></ul></ul><ul><ul><li>Seawater has 11 major constituents that make up more than 99.99% of all dissolved materials. </li></ul></ul><ul><ul><li>Although salinity may vary, the major constituents are well mixed and present in the same relative proportions. </li></ul></ul>Salinity
    2. 2. <ul><li>Chloride (Cl - ) 55.07% </li></ul><ul><li>Sodium (Na + ) 30.62% </li></ul><ul><li>Sulfate (SO 4 2- ) 7.72% </li></ul><ul><li>Magnesium (Mg 2+ ) 3.68% </li></ul><ul><li>Calcium (Ca 2+ ) 1.17% </li></ul><ul><li>Potassium (K + ) 1.10% </li></ul><ul><li>Bicarbonate (HCO 3 - ) 0.40% </li></ul><ul><li>Bromide (Br - ) 0.19% </li></ul><ul><li>Strontium (Sr 2+ ) 0.02% </li></ul><ul><li>Boron (B 3+ ) 0.01% </li></ul><ul><li>Fluoride (F - ) 0.01% </li></ul>Major Constituents of Seawater (% by weight)
    3. 3. <ul><ul><li>Determines the distribution of plants and animals that live in the ocean. </li></ul></ul><ul><ul><li>Affects other properties of seawater, such as its density and the amount of dissolved oxygen. </li></ul></ul>Why Study Salinity…
    4. 4. Significant Values <ul><ul><li>The average salinity of the world’s oceans is 35 ppt. </li></ul></ul><ul><ul><li>Freshwater has a salinity of <1 ppt. </li></ul></ul><ul><ul><li>Inshore waters with salinity values between 1 - 25 ppt are called brackish. </li></ul></ul><ul><ul><li>Waters with salinity greater than 40 ppt are called hypersaline. </li></ul></ul>
    5. 5. <ul><ul><li>Addition of salts to pure water causes an increase in density. Salinity can be calculated by measuring the specific gravity of a water sample using a hydrometer, correcting for the effect of temperature and converting the readings to salinity by using conversion tables. </li></ul></ul><ul><ul><li>Specific Gravity = density of sample </li></ul></ul><ul><ul><li> Density of pure water </li></ul></ul>Salinity Hydrometer Method
    6. 6. <ul><li>Be sure hydrometer is clean </li></ul><ul><li>Fill 500 mL graduated cylinder with sample water </li></ul><ul><li>Determine the temperature of your sample </li></ul><ul><li>Place the hydrometer in cylinder and let settle. It should not touch the cylinder walls, and should be read from the bottom of the meniscus. </li></ul><ul><li>Read the specific gravity from the hydrometer scale </li></ul><ul><li>Using the specific gravity and temperature values, determine salinity from salinity table in Teacher’s Guide </li></ul><ul><li>Read three times. The values should be within 2 ppt of the average. Discard outliers. </li></ul>Hydrometer Reading
    7. 8. <ul><ul><li>35 ppt standard: </li></ul></ul><ul><ul><ul><li>Measure out 17.5 g NaCl (table salt) and pour into a 500-mL graduated cylinder. </li></ul></ul></ul><ul><ul><ul><li>Fill the cylinder to the line with distilled water and carefully swirl the solution to mix the standard, until all salt crystals have dissolved. </li></ul></ul></ul><ul><ul><ul><li>Pour the solution into a 1-quart plastic bottle and label. </li></ul></ul></ul><ul><ul><li>Prepare a blank using 500 ml of distilled water. </li></ul></ul><ul><ul><li>Follow the directions for a water sample. </li></ul></ul><ul><ul><li>Check technique every six months. </li></ul></ul>Calibration - Hydrometer Method
    8. 9. <ul><ul><li>The amount of halogens (chloride, bromide, iodine, and fluoride) in the water sample (chlorinity) is determined using a silver nitrate titration method. The salinity of the sample can then be calculated using the following formula: </li></ul></ul><ul><ul><li>Salinity (ppt) = 1.80655 x Chlorinity (ppt) </li></ul></ul><ul><ul><li>Use a test kit that meet specifications described in the Tool Kit in the GLOBE Teacher’s Guide </li></ul></ul><ul><ul><li>Follow the instructions in the test kit to take three measurements. Values should be within the precision stated in the test kit specifications. Discard outliers and retake measurements. </li></ul></ul><ul><ul><li>Salinity titration method </li></ul></ul>
    9. 10. <ul><ul><li>Concentration of standard reflect composition of seawater. </li></ul></ul><ul><ul><li>38.6 ppt sea water titration standard: </li></ul></ul><ul><ul><ul><li>Measure out 17.5 g NaCl (table salt) and pour this into a 500-mL graduated cylinder. </li></ul></ul></ul><ul><ul><ul><li>Fill the cylinder to the line with distilled water and carefully swirl the solution to mix the standard, until all salt crystals have dissolved. </li></ul></ul></ul><ul><ul><ul><li>Pour the solution into a 1-quart plastic bottle and label. </li></ul></ul></ul><ul><ul><li>Follow directions for a water sample. </li></ul></ul><ul><ul><li>Calibrate every six months to check technique. </li></ul></ul>Calibration - Titration Method

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