Untitled Quiz

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Questions and Answers

What happens to the freezing point of a solution when the concentration of the solute is increased?

It fluctuates randomly without a definite trend.

It decreases relative to that of the pure solvent. (correct)

It increases higher than that of the pure solvent.

It remains the same as that of the pure solvent.

Which statement accurately describes the freezing point depression process in an osmometer?

The sample freezes immediately upon reaching 0 °C.

The stirring wire prevents ice formation completely.

Ice crystals' formation releases thermal energy and raises the temperature. (correct)

The temperature remains constant until all ice has formed.

What is one of the main principles governing the vapor pressure osmometer?

The vapor pressure of a solution varies randomly with temperature.

The solution's vapor pressure is independent of solute concentration.

The vapor pressure of a solution is higher than that of the pure solvent.

At a given temperature, the vapor pressure of a solution is less than that of the pure solvent. (correct)

What is a significant drawback of using a vapor pressure osmometer?

Volatile gases can erroneously increase the vapor pressure of the solvent. Signup and view all the answers

In clinical settings, what is a common use for an osmometer?

Monitoring diuretic therapy. Signup and view all the answers

What is osmosis primarily responsible for in cells?

Balancing water uptake and loss Signup and view all the answers

Which type of solution has a higher solute concentration outside the cell than inside?

Hypertonic solution Signup and view all the answers

What is osmolarity a measure of?

The number of solutes per liter of solution Signup and view all the answers

Which ion pair is produced when NaCl dissolves in water?

Na⁺ and Cl⁻ Signup and view all the answers

What could happen to a cell in a hypotonic environment?

It will rupture due to water influx Signup and view all the answers

Which of the following explains the importance of a cell membrane's semi-permeability?

It regulates movement of molecules and ions Signup and view all the answers

What is osmotic pressure?

The pressure preventing water from diffusing through a membrane Signup and view all the answers

Which statement is true regarding osmolarity in relation to cell survival?

Cells cannot survive if their surrounding osmolarity varies greatly Signup and view all the answers

What happens to cells in a hypertonic environment?

Cells lose water and may shrink. Signup and view all the answers

How is osmolality defined?

The number of solute particles in 1 kg of solvent. Signup and view all the answers

What does a higher osmolality indicate?

More solute particles in the solution. Signup and view all the answers

What is the normal range for human blood osmolality?

275 to 295 mOsm/kg. Signup and view all the answers

What do colligative properties depend on?

The number of solute particles present. Signup and view all the answers

Which type of osmometer measures freezing point depression?

Freezing point depression osmometer. Signup and view all the answers

What is the principle behind the use of freezing point depression in osmometers?

It is based on the colligative property of freezing point depression. Signup and view all the answers

When does osmolality increase in the human body?

During dehydration. Signup and view all the answers

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.