How to Determine if Supplied 70% Ethanol was the correct Proportion of Alcohol

In summary, to determine if the supplied 70% ethanol was the correct proportion of alcohol, you could use specific gravity with pure water as a reference. This can be done by preparing a few references over a range of compositions and using a hydrometer scaled in ethanol percentage. Alternatively, you can check a density table in a handbook for comparison.
  • #1
chunkytuna21
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0
You need to use 70% ethanol for an experiment. You only have a small quantity of 100% ethanol which is not enough to dilute and make the volume of 70% that you need. A chemistry friend of yours says he will make and distill some 70% ethanol for you. Unfortunately, your experiment doesn't work and you suspect the 70% ethanol is to blame. Suggest a way to determine whether the supplied 70% ethanol was the correct proportion of alcohol.


I'm thinking you could use specific gravity with pure water as a reference. Is that right? Any suggestions?
 
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  • #3
You would need to prepare a few references over a range of compositions, though.

I seem to recall that there is a small but significant change in volume when mixing ethanol with water. (10 mL of water and 10 mL of ethanol give something like 19.5 mL of the mixture, but it's been years since I observed this)
 
  • #4
There are even hydrometeres scaled not in g/mL but directly in ethanol %.

No need for reference solutions - it is enough to check density table in any handbook.

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1. How do I calculate the percentage of ethanol in a 70% ethanol solution?

To calculate the percentage of ethanol in a solution, you need to know the volume and concentration of the ethanol. In this case, the volume is 70% and the concentration is 70%, so the percentage of ethanol is simply 70%.

2. What are the potential sources of error when determining the correct proportion of alcohol in a 70% ethanol solution?

The potential sources of error include human error in measuring the volume or concentration of the ethanol, contamination of the solution, and improper calibration of equipment.

3. Can I use any type of alcohol to make a 70% ethanol solution?

No, a 70% ethanol solution specifically refers to a solution that is 70% ethanol and 30% water. Other types of alcohol, such as isopropyl alcohol, cannot be substituted for ethanol in this case.

4. How can I verify the accuracy of the supplied 70% ethanol solution?

To verify the accuracy of the supplied solution, you can use a densitometer or refractometer to measure the density or refractive index of the solution. These values should correspond to the expected values for a 70% ethanol solution.

5. What precautions should I take when determining the correct proportion of alcohol in a 70% ethanol solution?

It is important to use precise measuring equipment and techniques, as well as properly calibrate all equipment. Additionally, the solution should be stored and handled carefully to avoid contamination. It is also recommended to perform multiple measurements and calculations to ensure accuracy.

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