Video Transcript
Fill in the blank. Ethanol and ethanoic acid both mix in any proportion with water. Substances that mix in this way are said to be blank. (A) Blends, (B) mingled, (C) concocted, (D) miscible, or (E) immiscible.
Water molecules tend to have strong electrostatic interactions with the short-chain alcohol and carboxylic acid molecules. This is why ethanol, a short-chain alcohol, and ethanoic acid, a short-chain carboxylic acid, mix in any proportion with water. Ethanol is the structure on the left, and ethanoic acid is the structure on the right. The hydrogen atom of one molecule of water can form hydrogen bonds with the electronegative oxygen atom of adjacent alcohol or carboxylic acid molecules. Water molecules will readily break away from each other if they can form strong hydrogen bonds with polar alcohol or carboxylic acid molecules. This hydrogen bonding is primarily why ethanol and ethanoic acid are highly soluble in water.
So we know that ethanol and ethanoic acid mix well with water. But how do we describe the way that they mix? Let’s look at options from (A) to (E). Options (A), (B), and (C) are blends, mingled, and concocted, respectively. These are all quite ambiguous terms that are not especially scientific. Therefore, they’re not used by chemists to describe how two or more substances can combine together. For this reason, we can rule out options (A), (B), and (C).
Options (D) and (E), however, are regularly used by chemists. Option (D), miscible, is when substances can fully dissolve in each other at any concentration and form a single homogeneous solution, whereas option (E), immiscible, is the opposite. Immiscible substances do not form a homogeneous mixture when mixed. So oil and water will be examples of immiscible substances because when they are combined, they separate into layers. Therefore, the word immiscible does not describe the way the ethanol, ethanoic acid, and water mix. So option (E) is not the answer to this question.
As the word miscible describes species that can fully dissolve in each other at any concentration, therefore we can be confident that this word is used to describe how ethanol and ethanoic acid both mix in any proportion with water. Substances that mix in this way are said to be (D) miscible.
