What is the osmolarity of a typical oral rehydration solution (ORS) for infants that contains 95mEq/LNa+ , 25mEq/LK+ , 115mEq/LCl− , and 2.5% glucose? The molecular weight of glucose is 180 amu.

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To calculate the osmolarity of a solution, you need to know the concentrations (in molarity) of all the solutes in the solution. In this case, we are given the concentrations of Na+, K+, Cl-, and glucose in the oral rehydration solution (ORS) for infants.

First, let's convert the concentrations of Na+, K+, and Cl- from milliequivalents per liter (mEq/L) to millimoles per liter (mmol/L). To do this, we need to know the atomic weights/molecular weights of the respective ions:

Na+: Atomic weight = 23 amu (approximately)
K+: Atomic weight = 39 amu (approximately)
Cl-: Atomic weight = 35.5 amu (approximately)

1. Converting Na+ concentration:
Given concentration: 95 mEq/L
To convert to mmol/L, divide the concentration by the atomic weight:
95 mEq/L ÷ 23 g/mol ≈ 4.13 mmol/L

2. Converting K+ concentration:
Given concentration: 25 mEq/L
To convert to mmol/L, divide the concentration by the atomic weight:
25 mEq/L ÷ 39 g/mol ≈ 0.64 mmol/L

3. Converting Cl- concentration:
Given concentration: 115 mEq/L
To convert to mmol/L, divide the concentration by the atomic weight:
115 mEq/L ÷ 35.5 g/mol ≈ 3.24 mmol/L

Next, let's calculate the contribution of glucose to the osmolarity. The molecular weight of glucose is given as 180 amu (approximately).

4. Calculating the concentration of glucose in molarity (mol/L):
Given concentration: 2.5%
To convert to molarity, divide the percentage by 100 and multiply by the density of water (approximated as 1 g/mL or 1 kg/L) and divide by the molecular weight of glucose:
2.5% ÷ 100 × (1 kg/L) ÷ 180 g/mol ≈ 0.0139 mol/L

To calculate the osmolarity of the solution, you need to add up the osmolarities of each solute.

The osmolarity of a solution is equal to the sum of the concentrations (in mol/L) multiplied by the number of particles formed when the solute dissociates (referred to as the Van't Hoff factor). For sodium chloride (NaCl), the Van't Hoff factor is 2 because it dissociates into Na+ and Cl-.

For the oral rehydration solution (ORS) in question:
Osmolarity = (4.13 mmol/L + 0.64 mmol/L + 3.24 mmol/L + 0.0139 mol/L) × 2
Osmolarity ≈ 16.68 milliosmoles per liter (mosmol/L)

Therefore, the osmolarity of the typical oral rehydration solution (ORS) for infants is approximately 16.68 mosmol/L.