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Questions and Answers
What happens to the freezing point of a solution when the concentration of the solute is increased?
Which statement accurately describes the freezing point depression process in an osmometer?
What is one of the main principles governing the vapor pressure osmometer?
What is a significant drawback of using a vapor pressure osmometer?
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In clinical settings, what is a common use for an osmometer?
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What is osmosis primarily responsible for in cells?
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Which type of solution has a higher solute concentration outside the cell than inside?
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What is osmolarity a measure of?
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Which ion pair is produced when NaCl dissolves in water?
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What could happen to a cell in a hypotonic environment?
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Which of the following explains the importance of a cell membrane's semi-permeability?
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What is osmotic pressure?
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Which statement is true regarding osmolarity in relation to cell survival?
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What happens to cells in a hypertonic environment?
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How is osmolality defined?
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What does a higher osmolality indicate?
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What is the normal range for human blood osmolality?
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What do colligative properties depend on?
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Which type of osmometer measures freezing point depression?
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What is the principle behind the use of freezing point depression in osmometers?
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When does osmolality increase in the human body?
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Study Notes
Osmosis
- Water moves from a low solute concentration to a high solute concentration across a semi-permeable membrane
- This is driven by the difference in water potential between the two areas
- Osmosis is a vital process for cell survival, allowing cells to maintain a balanced internal environment
Osmotic Terms
- Solution: A homogeneous mixture of a solute (dissolved substance) and a solvent (dissolving medium)
- Isotonic solution: Same solute concentration inside and outside the cell
- Hypertonic solution: Higher solute concentration outside the cell than inside, causing water to move out of the cell
- Hypotonic solution: Higher solute concentration inside the cell than outside, causing water to move into the cell
Osmolarity
- Measures the number of osmoles (particles contributing to osmotic pressure) per liter of solution
- One mole of NaCl dissolves into two osmoles (Na⁺ and Cl⁻ ions) in solution
- Osmolarity is important for cell survival, as significant changes in the surrounding osmolarity can lead to cell lysis (bursting) or crenation (shrinking)
Osmolality
- Measures the number of solute particles in 1 kg of solvent
- It is expressed in milliosmoles per kilogram of water (mOsm/kg H₂O)
- A higher osmolality indicates a more concentrated solution
- Blood osmolality is typically 275 to 295 mOsm/kg, and changes in osmolality can indicate conditions like dehydration, diabetes, or shock
Colligative Properties
- These properties depend only on the number of solute particles in a solution, not their identity
- Colligative properties include vapor pressure depression, freezing point depression, boiling point elevation, and osmotic pressure
- They are used to measure the osmolality of solutions
Osmometer
- Used to measure the osmolality of biological samples like blood plasma and tears
- Measures the osmotic concentration in milliosmoles per kilogram (mOsm/kg)
Types of Osmometers
- Freezing Point Depression Osmometer: Measures the freezing point depression of the solution, based on the colligative property. This is the most common type used in clinical laboratories.
- Vapour Pressure Osmometer: Measures the vapor pressure of the sample relative to a pure solvent. This is not commonly used in clinical laboratories due to potential interference from volatile gases.
- Membrane Osmometer: Measures the osmotic pressure of a solution separated by a semipermeable membrane. This is not commonly used in clinical laboratories.
Freezing Point Depression Osmometer
- Principle: The freezing point of a solution is lowered compared to pure solvent as solute concentration increases.
- Process: The sample is supercooled below 0 °C. Ice crystals form and release thermal energy, raising the temperature. Equilibrium is reached when melting and freezing of ice balance, indicating the real freezing point of the sample.
Vapour Pressure Osmometer
- Principle: The vapor pressure of a solution is lower than that of the pure solvent. The difference in vapor pressure is measured.
- Applications: Monitoring diuretic therapy, quantitating sodium in isotonic solutions, studying colligative properties of parenteral solutions.
- Limitations: Volatile gases can interfere with the measurements, making this method unsuitable for clinical use.
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