Question Video: Recalling What the Mole Describes | Nagwa Question Video: Recalling What the Mole Describes | Nagwa

# Question Video: Recalling What the Mole Describes Physics • First Year of Secondary School

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Which of the following best describes the quantity that has the unit “mole”? [A] The number of equivalent parts that an object made of a substance consists of [B] The amount of a substance that is contained in an object

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### Video Transcript

Which of the following best describes the quantity that has the unit “mole”? (A) The number of equivalent parts that an object made of a substance consists of. (B) The amount of a substance that is contained in an object.

This question is asking us about what a mole is in terms of scientific units. A mole is a base SI unit and refers to the total amount of a substance. This could make us think that the answer is (B) because it leads us to believe that mole refers to the amount of a substance contained in an object. But this is not the correct definition, because a mole refers to a substance made up only of equivalent parts like atoms or molecules.

A statement as vague as “an amount of substance in an object” could reasonably refer to other units, like volume. So, let’s clarify what makes moles special. Recall that in the SI system, the base unit of mole refers to a specific number of equivalent parts. This number is 6.02214076 times 10 to the 23, usually shortened to 6.022 times 10 to the 23.

One mole of a substance refers to an object containing this number of equivalent parts. This is the well-known Avogadro number, named after the physicist and chemist Amedeo Avogadro.

As an example, let’s consider some water. In one mole of water, there are 6.022 times 10 to the 23 total H2O, or water, molecules. Each individual water molecule is made up of two hydrogen atoms and one oxygen atom. This means if we were to look at the atoms that make up our one mole of water, we would find that there are two times 6.022 times 10 to the 23 hydrogen atoms, that is, two moles of hydrogen atoms, and 6.022 times 10 to the 23 oxygen atoms, one mole of oxygen atoms.

Usually only atoms and molecules are counted in moles, given how big the number is. So, when we use moles, we are not just looking at some amount of a substance, we are looking at a highly specific number of atoms or molecules that an object consists of, which are all equivalent to each other. Based on this, it is safe to say that option (A) would be the most correct answer.

So, the answer to which statement best describes the quantity that has the unit mole is option (A): the number of equivalent parts that an object made of a substance consists of.

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