Question Video: Describing What an Impurity Is | Nagwa Question Video: Describing What an Impurity Is | Nagwa

Question Video: Describing What an Impurity Is Chemistry • Third Year of Secondary School

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Which of the following statements best describes what an impurity is? [A] A substance that can be separated from another substance [B] A wanted substance mixed within a desired substance [C] A substance finally dispersed in another substance [D] An unwanted substance mixed within a desired substance [E] A substance dissolved in another substance

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Video Transcript

Which of the following statements best describes what an impurity is? (A) A substance that can be separated from another substance. (B) A wanted substance mixed within a desired substance. (C) A substance finally dispersed in another substance. (D) An unwanted substance mixed within a desired substance. Or (E) a substance dissolved in another substance.

To answer this question, we need to identify which statement is the most accurate description of the term impurity. To help us better understand the term impurity, let’s consider two beakers.

The beaker on the left contains distilled water, so this beaker only contains water molecules. This is an example of a pure substance, a substance that contains only one type of element or compound. The beaker on the right contains a sample of river water. This sample contains water molecules in addition to dissolved ions and dispersed sand and silt particles.

River water is an example of an impure substance, a mixture of a desired substance with one or more undesired substances. These undesired substances are known as impurities. In the example of river water, the water is the desired substance, and the sand, silt, and dissolved ions are the impurities.

With this information in mind, let’s consider the answer choices. Answer choice (A) states that an impurity is a substance that can be separated from another substance. While it is true that sand, silt, and dissolved ions can be separated from the water, it is also true that the water can be separated from the sand, silt, and dissolved ions. So, statement (A) can be used to describe both the desired substance and the impurities, so it cannot be the answer to this question.

Statement (B) states that an impurity is a wanted substance mixed within a desired substance. As we know that impurities are undesired substances mixed within a desired substance, we can eliminate answer choice (B).

Answer choices (C) and (E) are similar. One describes impurities as finely dispersed in a substance, while the other describes impurities as dissolved in a substance. We can see in the example of river water that impurities can be both dissolved, like the ions dissolved in water, and dispersed, like the sand and silt particles dispersed in the water. So, neither of these statements is a completely accurate description of an impurity.

This leaves us with answer choice (D). We know that an impurity is an undesired or unwanted substance mixed within a desired substance, so this statement is the correct answer. Therefore the statement that best describes an impurity is answer choice (D), an unwanted substance mixed within a desired substance.

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