Lena Savoie
70% ethanol, also known as ethyl alcohol, is a widely used substance with a variety of applications, including cleaning, sanitization, and extraction. It is a colourless liquid with a pleasant odour and is highly flammable. To ensure the effectiveness of 70% ethanol for its intended use, it is important to verify its concentration. This can be achieved through various methods, such as using a graduated cylinder to measure the volume or employing more advanced techniques like FT-IR spectroscopy and gas chromatography.
| Characteristics | Values |
|---|---|
| Formula | C2H5OH |
| Miscibility with water | Completely miscible |
| Aqueous solution | 70% ethanol, up to 30% water |
| Colour | Colourless |
| Odour | Pleasant alcohol/solvent |
| Uses | Extraction solvent, tissue processing, histology, sterilisation, RNA extraction, DNA extraction, non-food sanitisation, cleaning, solvent |
| Toxicity | Relatively non-toxic |
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What You'll Learn
Use a graduated cylinder
To check if ethyl alcohol is 70% using a graduated cylinder, follow these steps:
Firstly, ensure you are wearing safety gear, including safety glasses and gloves, and that you have adequate space to perform the test. It is important to prioritise safety, especially when working with flammable substances. Have cleanup materials ready in case of any spills, and do not perform the test near an open flame or any potential sources of sparks.
Now, prepare your graduated cylinder. While a 50ml cylinder is sufficient, you can use a larger one if you prefer. Pour 10ml of ethyl alcohol into the cylinder. Then, add 2ml of water. Cover the cylinder with your finger or a suitable lid and shake the mixture for about a minute.
After shaking, wait for the contents to separate. The ethanol will mix with the water and settle at the bottom, while the remaining gasoline will rise to the top. Measure the volume of ethanol in millilitres. For example, if the ethanol layer is at the 70ml mark, subtract the 10ml of water added earlier, resulting in 60ml of ethanol.
Finally, calculate the percentage of ethanol. Divide the volume of ethanol by the total initial volume and multiply by 100. In this case, 60ml of ethanol divided by a total volume of 12ml, multiplied by 100, equals 500, indicating a concentration of 50% ethanol.
By following these steps and making the necessary calculations, you can determine whether your ethyl alcohol sample has a concentration of 70%.
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Compare to reference spectra
To compare the reference spectra of ethyl alcohol, you can use infrared spectrometry, which is an analytical technique used to monitor and measure the alcohol vapour content. This is often used in breathalyser tests, where an infrared breath-alcohol analyser is used to measure the absorption of selected wavelengths of infrared radiation after passage through a known volume of the breath sample.
The right-hand part of the infrared spectrum of ethanol, wavenumbers ~1500 to 400 cm-1, is considered the fingerprint region for the identification of ethanol and most organic compounds. This is due to a unique set of complex overlapping vibrations of the atoms of the ethanol molecule. The most distinct feature in the infrared spectrum of alcohols is the broad absorption band centred around wavenumbers 3400 to 3230 cm-1 due to O-H stretching vibrations, which are broadened by intermolecular hydrogen bonding.
In liquid films of alcohols like ethanol, the O-H is hydrogen-bonded with other ethanol molecules, and the O-H stretching vibrations occur at wavenumbers of 3500 to 3200 cm-1. However, in ethanol vapour, the molecules are free, and the O-H stretching vibrations occur at higher wavenumbers of 3670 to 3580 cm-1.
It is important to note that spectra from different instruments may vary, and concentration information may not always be available.
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Check for flammability
Ethyl alcohol is a highly flammable substance with a flashpoint below room temperature. Its flammability is due to its low flashpoint, which is the lowest temperature at which vapours of a combustible liquid can ignite. If the concentration of ethyl alcohol in a liquid is above 2.35% by mass, it is considered flammable. This concentration is well below the 70% mark, indicating that ethyl alcohol is highly flammable at 70%.
To check if ethyl alcohol is 70% and flammable, a simple test can be performed to observe its flammability characteristics. This test should be conducted outdoors or in a well-ventilated area due to the hazardous nature of ethyl alcohol. Here's a step-by-step guide:
- Prepare the materials: You will need a small amount of the ethyl alcohol solution, a glass or ceramic dish, and a source of ignition, such as a lighter or matches. It is recommended to have a fire extinguisher or water source nearby as a safety precaution.
- Pour a small amount of the ethyl alcohol solution into the dish: Ensure that the solution is at room temperature or slightly above (around 20-25°C). Do not perform the test if the temperature is close to or below the flashpoint of ethyl alcohol, which is below room temperature.
- Observe the solution's behaviour: At 70%, ethyl alcohol should have distinct flammable liquid behaviour. You may notice a strong smell or observe signs of evaporation as the alcohol vaporises.
- Introduce a source of ignition: Carefully hold the source of ignition (lighter or match) close to the dish containing the ethyl alcohol solution. Do not allow the ignition source to come into direct contact with the liquid.
- Observe for ignition: If the ethyl alcohol is 70% and flammable, it should ignite and produce a steady blue flame with a slight yellow tip. This indicates the presence of a volatile, flammable liquid.
- Remove the source of ignition: After observing the flame, remove the ignition source and ensure that the flame extinguishes without spreading or causing a larger fire. If the flame persists or spreads, immediately use the fire extinguisher or water source to control it.
By performing this test and observing the flammability characteristics, you can confirm if the ethyl alcohol solution is 70% and flammable. It is crucial to prioritise safety and conduct the test in a controlled manner to avoid any potential hazards or accidents.
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Check for colour
Colour can be used as a way to check the purity of ethyl alcohol. However, it is important to note that ethanol, or ethyl alcohol, is naturally a colourless liquid. So, to check its purity, you would need to mix it with other liquids or chemicals that will react with the ethanol to produce a colour.
One way to do this is through a process called colorimetric sensing, which involves using food colouring agents to identify the type of alcohol. For example, a green test solution prepared from brilliant blue FCF and tartrazine (1:5 v/v) will display different colours when dissolved in various alcohols, ranging from green to light blue, with a yellowish discolouration. This method can be used to qualitatively identify the type of alcohol and its concentration based on its unique colour and solubility characteristics.
Another way to check the purity of ethyl alcohol is through fractional distillation, which involves heating a mixture of ethyl alcohol and water to a specific temperature (e.g. 80 degrees Celsius) and then collecting the distilled liquid after it passes through a water jacket to condense the vapour. By measuring the volume of the distilled liquid and the volume of the remaining water, you can calculate the percentage of ethyl alcohol in the mixture.
It is important to note that these methods may require specialised equipment and may not be completely accurate without a sample of known purity to compare to. Additionally, the colour-sensing profiles for different types of alcohols may exhibit close similarities, making it difficult to distinguish between them based on colour alone.
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Check for toxicity
Ethyl alcohol, also known as ethanol, is a type of alcohol that is effective at killing a large range of viruses and germs. It is often used as an antiseptic and in cosmetic products such as eau de toilette, cologne, and mouthwash. While ethyl alcohol is generally considered safe for topical use, it can be toxic when consumed in certain quantities.
To check for toxicity, it is important to monitor for any signs or symptoms that may indicate ethyl alcohol poisoning. Some common side effects of ingesting ethyl alcohol include a drunk or buzzed feeling, impaired judgment, decreased attention, trouble with balance and speech, and mood changes. In more severe cases, ingestion can lead to blackouts, alcohol poisoning, and even death. It is important to note that the effects of ethyl alcohol can vary depending on factors such as body weight, metabolism, and the amount consumed.
If ethyl alcohol poisoning is suspected, it is crucial to seek immediate medical attention. Calling emergency services or poison control hotlines can provide access to timely assistance and expert guidance. In the case of ingestion, do not induce vomiting as it may cause chemical burns to the esophagus. Moving the affected individual to fresh air if the substance was inhaled, and flushing the skin with water if it was in contact with the skin, are also recommended. It is important to have information readily available, such as the person's age, weight, condition, the name of the product ingested, the time of ingestion, and the estimated amount consumed.
Medical professionals may perform a series of tests to assess toxicity and guide treatment. Blood tests are commonly used to determine the concentration of alcohol in the bloodstream. These tests can provide valuable information about the person's level of intoxication and help guide medical decisions. In addition to blood tests, healthcare providers may also order serum glucose tests to check blood sugar levels, serum electrolyte tests to assess dehydration, complete blood counts to evaluate various components of the blood, and blood urea nitrogen and creatinine tests to assess kidney function. Additionally, liver function tests, head CT scans, and urine tests may be conducted to comprehensively evaluate the individual's health and identify any potential complications.
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Frequently asked questions
70% ethyl alcohol is a mixture of 70% ethanol and 30% water. You can use an FT-IR spectrometer to analyze the solution and compare it to reference spectra. Alternatively, you can use a graduated cylinder to measure 70ml of ethanol and then add water until you reach a total volume of 100ml.
The formula for ethyl alcohol is C2H5OH or C2H6O.
Ethyl alcohol is also known as ethanol.
70% ethyl alcohol is widely used as a cleaner, solvent, and disinfectant. It is commonly used for non-food sanitization applications and in laboratories for histology, sterilization, RNA extraction, and DNA extraction.
