Deck 11: Measurement of Colligative Properties

Question 1

What is the purpose for calculating an osmolal gap?

A)This serves as a quality-control measure of osmolality measurement.
B)This serves as an indication of abnormal concentrations of unmeasured substances in the blood stream.
C)This is the method utilized to calibrate the osmometer.
D)This removes the need for direct measurement of osmolality.

Answer 1

This serves as an indication of abnormal concentrations of unmeasured substances in the blood stream.

Question 2

Calculate the osmolal gap, given the following data: measured osmolality = 366 mOsm/kg; sodium = 144 mEq/L; glucose = 5.0 mmol/L; BUN = 9.0 mg/dL.

A)64 mOsm/kg
B)70 mOsm/kg
C)74 mOsm/kg
D)208 mOsm/kg

Answer 2

70 mOsm/kg

Question 3

In the equation to estimate osmolality by calculation, why are glucose and BUN divided by 18 and 2.8, respectively?

A)to provide an estimate of the contribution of glucose and BUN to the total number of particles of each
B)to convert each from mg/L to mmol/L
C)to account for the number of charges on each molecule
D)both a and b

Answer 3

both a and b

Question 4

Suppose a lab measured serum osmolality on the same patient sample by freezing-point and vapor-pressure methods, and the osmolality measurement by the freezing-point method was found to be greater than the osmolality measurement by the vapor-pressure method.Which of the following is the most likely explanation for this discrepancy?

A)The difference in the two methods will always result in significantly different osmolalities.
B)overhydration of the patient
C)technologist error
D)the presence of unexpected volatile solutes in the patient sample

Question 5

Given that a normal albumin is approximately 40 g/L, a normal glucose is approximately 900 mg/L, and a normal BUN is approximately 100 mg/L, why is albumin (which has a much higher concentration) not considered in the equation to estimate osmolality?

A)Albumin concentration is so much higher than other components of the blood stream, its effect on osmolality is considered constant and thus not included in the calculation.
B)When considering the molecular weight of albumin, the high concentration becomes a very small number of moles, causing albumin not to be included in the calculation.
C)Albumin controls the movement of fluids in the body and does not influence osmolality.
D)Albumin is a transport protein in the blood stream, and osmolality is only influenced by components that are being transported by albumin, not albumin itself.

Question 6

Determine the calculated osmolality, given the following data: sodium = 140 mEq/L; glucose = 32 mmol/L; BUN = 30 mmol/L.

A)202 mOsm/kg
B)292 mOsm/kg
C)342 mOsm/kg
D)404 mOsm/kg

Question 7

The two methods used in the clinical laboratory to determine osmolality are:

A)osmotic pressure and boiling point
B)boiling point and freezing point
C)vapor pressure and osmotic pressure
D)freezing point and vapor pressure

Question 8

As the osmolality of a sample increases, the osmotic pressure ______, the boiling point _____, the freezing point ______, and the vapor pressure ______.

A)increases, increases, decreases, decreases
B)increases, decreases, increases, decreases
C)decreases, increases, decreases, increases
D)decreases, decreases, increases, increases

Question 9

The major clinical use for measuring urine osmolality is to evaluate ______, and the major clinical use for measuring colloid osmotic pressure is to detect conditions leading to ______.

A)the kidney's ability to dilute the urine, the kidney's ability to concentrate the urine
B)the kidney's ability to dilute the urine, pulmonary edema
C)the kidney's ability to concentrate the urine, the kidney's ability to dilute the urine
D)the kidney's ability to concentrate the urine, pulmonary edema

Question 10

The major measured contributor to serum osmolality is:

A)sodium
B)glucose
C)BUN
D)protein

Question 11

Osmometers utilizing the vapor-pressure colligative property of solutions are based on what principle?

A)An increase in the concentration of dissolved solutes decreases the vapor pressure generated because of a lack of volatility of the typical solutes.
B)An increase in the concentration of dissolved solutes increases the vapor pressure generated because of a lack of volatility of the typical solutes.
C)An increase in the concentration of dissolved solutes decreases the vapor pressure generated because of an increased volatility of the typical solutes.
D)An increase in the concentration of dissolved solutes increases the vapor pressure generated because of an increased volatility of the typical solutes.

Question 12

All of the following variables are needed to calculate a stool osmolal gap except:

A)stool glucose level
B)stool sodium level
C)stool potassium level
D)measured stool osmolality

Question 13

Which of the following anticoagulants will contribute the least to plasma osmolality?

A)indoacetic acid
B)sodium fluoride-potassium oxalate
C)heparin
D)EDTA

Question 14

Osmometers utilizing the freezing point colligative property of solutions are based on what principle?

A)1 osmole of nonionizing substance dissolved in 1 kilogram of water raises the freezing point 1.86°C.
B)1 osmole of nonionizing substance dissolved in 1 kilogram of water lowers the freezing point 1.86°C.
C)Increased solute concentration will raise the freezing point of water in direct proportion to a NaCl standard.
D)Deceased solution concentration will lower the freezing point of water in direct proportion to a NaCl standard.

Question 15

Osmolality measurements depend on:

A)the molecular weight of particles in solution
B)the kind of particles in solution
C)the number of particles in solution
D)all of the above

Question 16

In the equation to estimate osmolality by calculation, why is the sodium multiplied by two?

A)Sodium is present in body fluids in twice the concentration of other ions.
B)Sodium has a valence of two.
C)The equation accounts for sodium and its corresponding anion.
D)This factor accounts for the fact that sodium may be bound to chloride (NaCl) or to bicarbonate (NaHCO3).

Question 17

Determine the calculated osmolality given the following data: sodium = 135 mEq/L; glucose = 95 mg/dL; BUN = 10 mg/dL.

A)240 mOsm/kg
B)279 mOsm/kg
C)375 mOsm/kg
D)480 mOsm/kg