What have the compounds in each of these pairs in common? How could you distinguish one from the other? (a) CH3COOH and CH3OH? (b) C2H5OH and H2O?
(a) The compounds in pair (a), CH3COOH (acetic acid) and CH3OH (methanol), both contain carbon (C), hydrogen (H), and oxygen (O) atoms. They are both organic compounds.
To distinguish between CH3COOH and CH3OH, one possible method is to conduct a chemical reaction. Acetic acid (CH3COOH) can be distinguished from methanol (CH3OH) by reacting them separately with a base, such as sodium bicarbonate (NaHCO3). When acetic acid reacts with a base, it produces carbon dioxide gas (CO2) and water (H2O). This reaction can be observed by effervescence (bubbling), and the presence of carbon dioxide can be confirmed by passing the gas through lime water, which will turn cloudy due to the formation of calcium carbonate (CaCO3).
On the other hand, methanol does not react with sodium bicarbonate in the same way, as it is not an acidic compound. So, if there is no effervescence or cloudiness observed when methanol is reacted with sodium bicarbonate, it indicates that the compound is methanol, not acetic acid.
(b) The compounds in pair (b), C2H5OH (ethanol) and H2O (water), both contain carbon (C), hydrogen (H), and oxygen (O) atoms. Ethanol is an organic compound, while water is an inorganic compound.
To distinguish between C2H5OH (ethanol) and H2O (water), one method is to conduct a flammability test. Ethanol is highly flammable, and it burns with a blue flame, producing carbon dioxide gas (CO2) and water vapor (H2O). On the other hand, water itself does not burn, so if a liquid substance produces a blue flame and produces carbon dioxide and water vapor upon burning, it indicates the presence of ethanol.
It is important to note that these methods only provide a general indication and should be carried out under appropriate laboratory conditions by trained individuals.
To determine what these pairs of compounds have in common and how to distinguish one from the other, we need to analyze their chemical structures and properties.
(a) CH3COOH and CH3OH:
- Commonality: In both compounds, carbon (C), hydrogen (H), and oxygen (O) are present.
- Difference: The main distinction between these two compounds is the presence of a carboxyl (-COOH) functional group in CH3COOH, which is absent in CH3OH. The carboxyl group consists of a carbonyl group (C=O) and a hydroxyl group (-OH) attached to the same carbon atom.
To distinguish between CH3COOH and CH3OH, you can use the following methods:
1. pH Test: CH3COOH is a weak acid, so it will lower the pH of a solution. You can test the pH of a solution containing the compound using pH indicators or a pH meter. CH3OH, on the other hand, is a neutral compound and will not significantly affect the pH of a solution.
2. Smell: CH3COOH has a distinctive, pungent vinegar-like smell, while CH3OH has a characteristic alcoholic smell. By using your sense of smell, you can identify the compounds based on their odor.
3. Chemical Tests: Various chemical reactions can be used to differentiate between these compounds. For example, a reaction with sodium carbonate will produce carbon dioxide gas (CO2) with CH3COOH, while no gas will be formed with CH3OH.
(b) C2H5OH and H2O:
- Commonality: Both compounds contain hydrogen (H) and oxygen (O).
- Difference: The key distinction lies in the arrangement of the atoms. C2H5OH, also known as ethanol, consists of two carbon atoms (C2), while H2O, also known as water, consists of two hydrogen atoms (H2).
To differentiate between C2H5OH and H2O, you can employ the following approaches:
1. Boiling Point: Ethanol has a higher boiling point (78.5 °C) compared to water (100 °C) under normal conditions. You can heat the compounds and observe the temperature at which they boil to identify them.
2. Combustion Test: Ethanol is a flammable liquid and will combust in the presence of a flame, producing a blue, non-sooty flame. Water, being non-flammable, will not burn. By carefully igniting a sample of each compound, you can observe their combustion behavior.
3. Solubility Test: Ethanol is soluble in water. Therefore, if you mix C2H5OH with H2O, they will readily mix and form a homogeneous solution. On the other hand, if you try to mix water with water, no further solubility change will occur.
It is important to note that conducting these tests should be done with caution and in compliance with safety guidelines.