Calculating a glucose solution involves determining the amount of glucose needed to achieve a specific concentration in a given volume of solvent (usually water). This calculation often involves working with molarity and dilution principles. Here's a breakdown:
Understanding the Basics
- Molarity (M): Moles of solute (glucose) per liter of solution.
- Molecular Weight of Glucose (C6H12O6): Approximately 180.16 g/mol.
- Dilution: Reducing the concentration of a solution by adding more solvent.
Calculating Glucose Solution from Solid Glucose
Here's how to calculate how much solid glucose you need to make a specific molarity solution:
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Determine the desired molarity (M) and volume (V) of the solution. For example, you want to make 500 mL (0.5 L) of a 0.1 M glucose solution.
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Calculate the number of moles of glucose needed:
- Moles = Molarity (M) x Volume (V) in Liters
- Moles = 0.1 M x 0.5 L = 0.05 moles
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Calculate the mass of glucose needed:
- Mass (g) = Moles x Molecular Weight (g/mol)
- Mass = 0.05 moles x 180.16 g/mol = 9.008 g
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Dissolve the calculated mass of glucose in the solvent: Dissolve 9.008 g of glucose in enough water to bring the final volume to 500 mL.
Calculating Glucose Solution from a Stock Solution
Sometimes, you need to make a glucose solution from a more concentrated stock solution. This involves dilution.
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Determine the desired molarity (M1) and volume (V1) of the final solution. Let's say you want 100 mL (0.1 L) of a 0.05 M glucose solution.
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Determine the molarity (M2) of the stock solution. For example, your stock solution is 1 M.
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Use the dilution equation: M1V1 = M2V2
- Where:
- M1 = Desired molarity (0.05 M)
- V1 = Desired volume (0.1 L)
- M2 = Stock solution molarity (1 M)
- V2 = Volume of stock solution needed (unknown)
- Where:
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Solve for V2:
- V2 = (M1V1) / M2
- V2 = (0.05 M x 0.1 L) / 1 M = 0.005 L or 5 mL
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Prepare the solution: Take 5 mL of the 1 M stock solution and add enough water to bring the final volume to 100 mL.
Summary Table
| Step | Calculation/Action | Example |
|---|---|---|
| From Solid | ||
| 1. Moles Needed | Moles = Molarity (M) x Volume (V) in Liters | 0.1 M x 0.5 L = 0.05 moles |
| 2. Mass Needed | Mass (g) = Moles x Molecular Weight (g/mol) | 0.05 moles x 180.16 g/mol = 9.008 g |
| From Stock | ||
| 1. Dilution Equation | M1V1 = M2V2 | (0.05 M)(0.1 L) = (1 M) V2 |
| 2. Volume of Stock Needed | V2 = (M1V1) / M2 | V2 = (0.05 M x 0.1 L) / 1 M = 0.005 L (5 mL) |
Key Considerations
- Always use accurate weighing and volumetric techniques for precise solutions.
- Ensure the glucose is fully dissolved in the solvent.
- Use appropriate containers and label your solutions clearly.
- When diluting acids (although not the case with glucose), always add acid to water, not the other way around, to avoid excessive heat generation.
