Questions to Answer Activity 2 PDF

Summary

This document contains questions about flammability, charring, and solubility tests in chemistry. The questions cover concepts like ethanol combustion, charring of organic and inorganic compounds, and the solubility of different substances in various solvents.

Full Transcript

**QUESTION 1** A. **Flammability:** 1. **Ethanol**: When ethanol (CH3CH2OH) burns, it undergoes complete combustion if there is enough oxygen present. This results in a blue flame, which indicates the formation of carbon dioxide (CO2) and water (H2O) as combustion products. Ethanol b...

**QUESTION 1** A. **Flammability:** 1. **Ethanol**: When ethanol (CH3CH2OH) burns, it undergoes complete combustion if there is enough oxygen present. This results in a blue flame, which indicates the formation of carbon dioxide (CO2) and water (H2O) as combustion products. Ethanol burns more cleanly than other hydrocarbons because it has a relatively simple structure, with fewer carbon atoms, allowing for more efficient combustion. Hydrocarbons like coal or candle wax may produce yellow flames due to incomplete combustion, which releases carbon monoxide (CO) and soot (carbon particles) into the air. 2. **Water (H2O)**: Water doesn't burn because it is a combustion product itself. It results from the reaction between hydrogen and oxygen, which releases energy as heat and light. Once water is formed, it cannot be burned again because it has already gone through the combustion process, meaning it has no further chemical energy available to release through combustion. In essence, organic compounds like ethanol can burn, producing flames that vary based on the combustion process. Ethanol typically burns with a blue flame under complete combustion. Whereas., inorganic compounds like water do not burn because they are stable combustion products, with no energy left to release through further burning. McCarthy, J., & Crean, A. (2017) Ashish, S. (2017). **B. Charring:** The difference in charring between organic and inorganic compounds, such as sugar and salt, can be explained by their distinct chemical structures and bonding. 1. **Organic Compounds**: Organic compounds, like sugar, contain carbon-based structures with covalent bonds between atoms. When sugar is heated, it undergoes thermal decomposition because its covalent bonds break down. Initially, sugar melts, then undergoes caramelization, followed by decomposition into carbon and water. As heat continues, the sugar burns, producing char, primarily carbon. This explains why sugar turns from brown to black as it burns. The release of water vapor contributes to the moisture observed during the process. 2. **Inorganic Compounds**: Inorganic compounds, like salt (sodium chloride), are ionic compounds with strong ionic bonds between positive and negative ions. These compounds are much more thermally stable compared to organic compounds. When salt is heated, it does not melt or decompose under typical conditions because the ionic bonds require significantly higher temperatures to break. The color change observed in salt is likely due to impurities or reactions with other elements or compounds during heating, rather than charring. In essence, organic compounds contain carbon and undergo thermal decomposition, leading to charring when heated. Whereas, inorganic compounds are more thermally stable and do not char; their color changes could be caused by impurities or chemical reactions. McMurry, J. (2016). C. **Solubility test** **Test Tube A: Naphthalene in Chloroform** Observation: Naphthalene dissolves quickly in chloroform. Naphthalene is a non-polar molecule, and chloroform is also non-polar. According to the principle \"like dissolves like,\" non-polar substances dissolve well in non-polar solvents. In this case, naphthalene dissolves readily in chloroform because both have similar non-polar properties. **Test Tube B: Sodium Chloride in Chloroform** Observation: Sodium chloride does not dissolve in chloroform. Sodium chloride (NaCl) is an ionic compound, meaning it consists of positively and negatively charged ions. Chloroform, however, is a non-polar solvent and cannot interact effectively with these charged ions. Ionic compounds dissolve well in polar solvents, where the strong interactions between water molecules and the ions can overcome the ionic bonds in the solid. Chloroform lacks these interactions, so NaCl remains undissolved. **Test Tube C: Naphthalene in Water** Observation: Naphthalene does not dissolve in distilled water. Naphthalene is non-polar, while water is a polar solvent with strong hydrogen bonding. Non-polar substances cannot interact with water molecules effectively because they do not form hydrogen bonds or dipole interactions. The energy needed to break the hydrogen bonds in water is not compensated by the interactions between naphthalene and water, leading to poor solubility. **Test Tube D: Sodium Chloride in Water** Observation: Sodium chloride dissolves quickly in distilled water. Sodium chloride is ionic, and water is a polar solvent. Water molecules interact strongly with the Na+ and Cl- ions, breaking apart the ionic bonds in the salt and surrounding the ions. This interaction is strong enough to dissolve the salt, demonstrating the principle that polar solvents are effective at dissolving ionic compounds due to their ability to stabilize the ions in solution.s **QUESTION 2:** The solubility of organic compounds in water or other solvents is largely influenced by their molecular structure. Key structural factors that affect solubility include: a. **Polarity**: Polar compounds dissolve well in polar solvents (like water), while nonpolar compounds dissolve in nonpolar solvents (like oils). This is explained by the principle "like dissolves like." For example, compounds with polar functional groups like hydroxyl (-OH) or carboxyl (-COOH) form hydrogen bonds with water, increasing their solubility. b. **Size and Molecular Weight:** Smaller organic molecules with low molecular weight are generally more soluble in water because they are easier to surround and interact with solvent molecules. As molecular size increases, solubility decreases because larger molecules have stronger intermolecular forces and are more difficult for solvent molecules to break apart. c. **Hydrocarbon Chains**: Organic compounds with long hydrocarbon chains (which are nonpolar) tend to be less soluble in water. The longer the nonpolar chain, the less interaction with polar solvents, reducing solubility. For instance, fatty acids with long chains are less soluble in water compared to short-chain ones. d. **Functional Groups**: The presence of functional groups like hydroxyl (-OH), amine (-NH2), and carboxyl (-COOH) makes organic compounds more soluble in polar solvents because they allow for hydrogen bonding. In contrast, nonpolar groups like methyl (-CH3) reduce solubility in water. e. **Branching**: Organic molecules that are more branched tend to have higher solubility in water than their straight-chain counterparts. Branching decreases intermolecular interactions, making it easier for the solvent molecules to interact with the compound. Example: Ethanol (C2H5OH) is highly soluble in water because of its small size and polar -OH group, which can form hydrogen bonds with water. On the other hand, hexane (C6H14), a nonpolar compound with a long hydrocarbon chain, is not soluble in water. McMurry, J. (2016) **QUESTION 3:** Liquid organic compounds are volatile because they have high vapor pressure and low water solubility, which allows them to evaporate easily into the air. The high vapor pressure means that these compounds can transition from a liquid to a gas at room temperature. This occurs because the molecules of volatile organic compounds (VOCs) are not strongly bound together, allowing them to escape into the atmosphere. For example, products like paints, cleaning agents, and fuels contain VOCs that evaporate readily, releasing gases into the air. This volatility is why VOCs are commonly found as air pollutants both indoors and outdoors. (US EPA, 2023

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