Question

(a) Classify each of the following as a pure substance, a solution, or a heterogeneous mixture: a gold coin, a cup of coffee, a wood plank. (b) What ambiguities are there in answering part (a) from the descriptions given?

Short answer

(a) A gold coin can be classified as a pure substance if it is made of pure gold, or as a homogeneous mixture if it is an alloy; a cup of coffee is a solution (homogeneous mixture); a wood plank is a heterogeneous mixture. (b) The main ambiguities in answering part (a) come from the lack of information on the compositions of the gold coin and the wood plank, making it difficult to definitively classify them.

Step-by-step solution

Define the terms

A pure substance is a material that has a constant composition and cannot be separated into further components by physical means. It can either be an element or a compound. A solution is a type of homogeneous mixture, where the particles are uniformly distributed, and the composition does not vary from one region to another. A heterogeneous mixture, on the other hand, has a non-uniform composition with visibly different regions having different properties.

Analyze the gold coin

A gold coin appears to be of uniform composition and is made up primarily of the element gold. It may have some impurities or alloying elements, like copper, to improve durability. If we assume that the coin is made of pure gold, we can classify it as a pure substance. If the gold coin is an alloy, we classify it as a homogeneous mixture, since the components are uniformly distributed. However, based on the given description, we cannot definitively determine the exact composition.

Analyze the cup of coffee

A cup of coffee usually consists of coffee particles dissolved or suspended in water, along with other components like sugar and milk. The coffee particles are uniformly distributed throughout the liquid, making it a solution (a type of homogeneous mixture).

Analyze the wood plank

A wood plank is a complex material made up of cellulose, hemicellulose, and lignin, as well as other trace elements. The composition of wood varies throughout, depending on the type and age of the wood, and the various components appear to be non-uniformly distributed. Therefore, we can classify a wood plank as a heterogeneous mixture.

Discuss ambiguities in part (a)

There are some ambiguities in answering part (a) based on the given descriptions. For example, we cannot determine with certainty whether the gold coin is a pure substance or a homogeneous mixture, as we have limited information about its composition. Similarly, the composition of a wood plank could potentially be considered to vary depending on factors such as the type of wood and what part of the plank the sample is taken from. However, these ambiguities primarily relate to the limited information provided about the items and not the classification process itself.