Question

You are given samples of 1-propanol, pentane, and ethanoic acid. Describe how you would use chemical tests, such as aqueous solubility and acid-base indicators, to distinguish among the three compounds.

Short answer

1-propanol will be soluble in water without changing the color of litmus paper. Pentane will be insoluble in water and also will not change the color of litmus paper. Ethanoic acid will be soluble and turns litmus paper red.

Step-by-step solution

Test solubility in water

Determine the solubility of each compound in water. 1-propanol, being an alcohol, will mix with water completely due to its ability to form hydrogen bonds. Pentane, a hydrocarbon, will not mix with water due to its nonpolar nature. Ethanoic acid will also mix with water as it can form hydrogen bonds and will ionize to form acetate ions and hydronium ions.

Use an acid-base indicator

Use an acid-base indicator (like litmus paper) to test the acidity of the compounds. 1-propanol should not cause a significant color change as it is not acidic or basic. Ethanoic acid will turn litmus paper red, confirming it as an acid. Pentane will not cause a color change as it is neutral and non-reactive with the indicator.

Deduce identities based on results

Based on the solubility test and the litmus paper test, you can deduce which compound is which. The one that is soluble in water but doesn't affect the litmus paper is 1-propanol. The one that is insoluble in water is pentane. The one that is soluble in water and turns litmus paper red is ethanoic acid.

Key concepts

Solubility in Water

Solubility in water is a crucial concept when distinguishing among organic compounds. Solubility refers to the ability of a substance to dissolve in a solvent, such as water. Organic compounds exhibit differing solubility in water based on their molecular structure and the presence of functional groups capable of forming hydrogen bonds.

For example, 1-propanol, an alcohol, has a hydrophilic (water-loving) hydroxyl group (-OH) that allows it to engage in hydrogen bonding with water molecules, leading to complete solubility. On the other hand, pentane is a nonpolar hydrocarbon without such functional groups, rendering it insoluble in water. In contrast, ethanoic acid possesses both a hydroxyl group and a carbonyl group that can participate in hydrogen bonding and ionization, promoting its solubility and its behavior as an acid when interacting with water.

Acid-Base Indicators

Acid-base indicators are compounds that change color in response to the pH level of a solution, thus providing a visual way to determine the acidity or basicity of a substance. These indicators help clarify the presence of acidic or basic functional groups in organic compounds.

For instance, litmus paper is a common indicator which turns red in acidic solutions and blue in basic solutions. When used in our chemical tests, it reveals that ethanoic acid, with its acidic properties, turns the litmus paper red, indicating its acidic nature. Contrastingly, 1-propanol does not significantly affect the indicator due to its neutral characteristic, and pentane shows no reaction because it is a nonpolar compound and does not interact with the indicator.

Hydrogen Bonding

Hydrogen bonding, a significant type of chemical bond, occurs when a hydrogen atom covalently bonded to a highly electronegative atom, such as oxygen or nitrogen, experiences an attractive force from another electronegative atom with a lone pair of electrons.

This interaction is much weaker than a covalent bond but stronger than other intermolecular forces. In the context of our problem, 1-propanol forms hydrogen bonds due to its hydroxyl group, and ethanoic acid can do so as well - both leading to greater solubility in water. Exploring hydrogen bonding is pivotal when contemplating the solubility of substances in water and their interactions with other molecules, such as in the case of acid-base reactions.