Making a 90% ethanol solution from 100% ethanol (also known as absolute ethanol) is a straightforward process involving simple dilution. Understanding the process correctly is crucial, especially if you're working in a laboratory setting or for any application where precision is critical. This guide will walk you through the steps, explaining the calculation and emphasizing safety precautions.
Understanding the Dilution Process
Diluting ethanol involves reducing its concentration by adding a solvent, typically distilled water. The key to accurate dilution is understanding the ratio of ethanol to water needed to achieve the desired concentration. We will use a simple formula:
C1V1 = C2V2
Where:
- C1 is the initial concentration (100% ethanol)
- V1 is the initial volume of ethanol (this is what you'll determine based on your needs)
- C2 is the final concentration (90% ethanol)
- V2 is the final volume of the solution
Calculating the Required Volumes
Let's say you need 100ml of 90% ethanol solution. Here's how to calculate the volumes:
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Identify your variables:
- C1 = 100%
- V1 = ? (This is what we need to find)
- C2 = 90%
- V2 = 100ml
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Apply the formula: 100% * V1 = 90% * 100ml
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Solve for V1: V1 = (90% * 100ml) / 100% = 90ml
This means you need 90ml of 100% ethanol.
- Calculate the water volume: To get 100ml of the final solution, you'll need 100ml (total) - 90ml (ethanol) = 10ml of distilled water.
Step-by-Step Dilution Procedure
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Gather your materials: You'll need 100% ethanol, distilled water, a graduated cylinder (or other accurate measuring device), a mixing flask or beaker, and safety goggles. Always wear appropriate safety glasses.
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Measure the ethanol: Carefully measure 90ml of 100% ethanol using the graduated cylinder.
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Add the water: Add 10ml of distilled water to the flask containing the ethanol.
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Mix thoroughly: Gently swirl or stir the mixture to ensure the ethanol and water are completely combined. Avoid vigorous shaking, as this can cause splashing and potential hazards.
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Label and store: Label the container clearly indicating the contents (90% Ethanol Solution), the date of preparation, and any relevant safety information. Store the solution in a suitable container away from ignition sources.
Safety Precautions: Handling Ethanol
- Flammability: Ethanol is highly flammable. Keep it away from open flames, sparks, and heat sources.
- Toxicity: Ethanol is toxic if ingested. Avoid skin and eye contact. Work in a well-ventilated area.
- Proper Disposal: Dispose of any unused ethanol or solutions according to local regulations.
Important Note: The accuracy of your final solution depends heavily on the precision of your measurements. Using accurate measuring devices is critical. If you require a highly precise solution, you may consider using analytical balances for more accurate measurements. Always follow safety guidelines when handling chemicals.
