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20 Cards in this Set
- Front
- Back
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What is an Osmometer?
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An instrument for measuring solute particles in a solution
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What properties have to be considered in osmometry?
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Colligative; how each would need to change to incr. osmolality.
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What are the 4 colligative properties? Which concern osmometry?
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1. Osmotic pressure
2. Vapor pressure - this. 3. Boiling point 4. Freezing point - & this. |
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How does Vapor pressure vary with increasing osmolality?
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For every mOsm, Pvap decreases 0.3 mm Hg
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How does Freezing pnt vary with increasing osmolality?
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For every mOsm, freezing pnt decreases 1.86 ' C.
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What IS vapor pressure?
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The pressure needed to prevent molecules from escaping from a liquid.
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What happens to Pvap when you add solute?
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Decreases; need less pressure to keep from evaporating.
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On what principle does an osmometer operate?
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the principle of freezing point depression.
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What is the name of the most common brand of osmometer?
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Fiske
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What are the 5 components of an osmometer?
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1. Cooling bath
2. STirrer 3. Thermister probe 4. Readout 5. Measuring potentiometer |
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What's in the cooling bath? How does it work?
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Antifreeze; the patient sample gets lowered into it.
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What 2 things stick into the patient sample?
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-Stirrer to agitate vigorously
-Thermister probe |
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How does a thermistor probe work?
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Its resistance changes with temperature changes, giving a readout that is proportional.
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On what point of the temp versus time curve is the osmolarity reading taken?
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at the plateau region - the heat of fusion, equilibrium temp between thawing and freezing.
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On the osmometer, what is the
-Input transducer? -Output transducer? |
Input = thermistor
Output = Wheatstone bridge |
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How do you calibrate the osmometer?
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By first using a standard of 300 mOsm; setting one potentiometer on the wheatstone brdg at 300;
Use 500 mOsm standard and do same w/ other POT. Use Calibrated pot to set zero; Measure patient sample, adjust final Pot for value. |
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How does the Wescor Vapor pressure osmometer work?
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Same concept as the osmometer, but you replace the graph values of heat of fusion for "Heat of condensation", between liquid and pressure.
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What are 2 problems with osmometry?
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-Sample volume the holder holds 2-3 ml of plasma
-Vat of Antifreeze maintanence. |
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What are 3 advantages of Osmometry?
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-Small sample size
-Short time period of measurement. -Sample is not altered in anyway. |
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What is the Dew point?
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The temperature at which vapor in air goes into the liquid phase because of atmospheric pressure.
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