Which of the following is isotonic with 15%=(w/w) glucose (specific gravity=12)

1. 1M CaCl2
2. 0.5N CaCl2
3. 0.5M NaCl
4. 0.5M urea

To determine which solution is isotonic with a 15% (w/w) glucose solution, we first need to understand what isotonic means. An isotonic solution has the same osmotic pressure as another solution, which means it will not cause cells to swell or shrink when placed in it. In this case, we are comparing the osmotic pressure of the given solutions to that of the 15% glucose solution.

Calculating the Osmolarity of 15% Glucose

First, let’s calculate the osmolarity of the 15% (w/w) glucose solution. The specific gravity of the solution is given as 1.2, which means that 100 mL of this solution weighs 120 grams. To find the number of moles of glucose in this solution, we need to know the molar mass of glucose (C6H12O6), which is approximately 180 g/mol.

• Weight of glucose in 100 mL = 15% of 120 g = 18 g
• Moles of glucose = 18 g / 180 g/mol = 0.1 moles

Since glucose does not dissociate in solution, the osmolarity of the 15% glucose solution is simply the number of moles of glucose per liter. To find the volume in liters, we convert 100 mL to liters (0.1 L):

• Osmolarity = 0.1 moles / 0.1 L = 1 M

Evaluating the Other Solutions

Now, let’s evaluate the osmolarity of the other solutions provided:

1M CaCl2

Calcium chloride (CaCl2) dissociates into three ions: one Ca²⁺ and two Cl⁻. Therefore, the osmolarity is:

• Osmolarity = 1 M × 3 = 3 Osm/L

0.5N CaCl2

Normality (N) is based on the number of equivalents. For CaCl2, 0.5N means it provides 0.5 equivalents of Ca²⁺ ions. Since it also dissociates into three ions:

• Osmolarity = 0.5 N × 3 = 1.5 Osm/L

0.5M NaCl

Sodium chloride (NaCl) dissociates into two ions: Na⁺ and Cl⁻. Thus, the osmolarity is:

• Osmolarity = 0.5 M × 2 = 1 Osm/L

0.5M Urea

Urea does not dissociate in solution, so its osmolarity is simply:

• Osmolarity = 0.5 M = 0.5 Osm/L

Comparing Osmolarities

Now, let’s summarize the osmolarities we calculated:

• 15% Glucose: 1 Osm/L
• 1M CaCl2: 3 Osm/L
• 0.5N CaCl2: 1.5 Osm/L
• 0.5M NaCl: 1 Osm/L
• 0.5M Urea: 0.5 Osm/L

From this comparison, we can see that the solutions that are isotonic with the 15% glucose solution (1 Osm/L) are:

• 0.5M NaCl
• 15% Glucose

In conclusion, the solution that is isotonic with a 15% (w/w) glucose solution is 0.5M NaCl. This means that if you were to place cells in either of these solutions, they would maintain their shape and not undergo osmotic pressure changes.