Video: Identifying the Nonpolar Liquid in a Set of Chemical Formulas

Which of the following corresponds to a nonpolar liquid? [A] SO₂ [B] KBr [C] CF₄ [D] HCl [E] C₆H₆


Video Transcript

Which of the following corresponds to a nonpolar liquid? A) SO₂, B) KBr, C) CF₄, D) HCl, E) C₆H₆.

In the question here, we’re being asked to identify a substance that is a liquid. That is a liquid under normal conditions. We will assume a liquid at room temperature and atmospheric pressure. In a liquid, the particles are very close together and they’re in chaotic random motion. In this question, we’re also being asked to identify a nonpolar substance. Nonpolar substances contain nonpolar molecules. Those molecules where there’s no separation of charge across the molecule. Polar molecules must at least contain polar bonds. A polar bond is a covalent bond in which there is a separation of charge between one end and the other. This is caused by a significant difference in electron negativity between the two atoms in the bond.

In the diagram here, atom B is more electronegative than atom A. Atom B attracts the electron pair to itself more than A, so there would be more electron density at the end of the bond closest to atom B than at atom A. We would say the bond is permanently polarized. This is indicated by the symbols 𝛿 plus and 𝛿 minus. Now, polar molecules must not only contain polarized bonds, but they must also contain a separation of charge across the entire molecule. Polar molecules contain an end or side, which is slightly negative and one which is slightly positive. There is overall separation of charge from top to bottom or left to right.

In the diagram here, which shows a molecule of water, there is an obvious negative end and an obvious positive end to the molecule. So whilst water is a polar molecule due to its shape and lack of symmetry, we must remind ourselves that we are looking for a nonpolar molecule in this question. Let us look at each molecule in more detail to identify its physical state at room temperature and pressure and then to decide whether it is a polar or a nonpolar molecule. SO₂ or sulphur dioxide is a gas at room temperature. It’s easily produced by heating solid sulphur strongly enough in air. Sulphur dioxide is also a polar molecule due to its nonlinear shape and the fact that oxygen is more electronegative than sulphur. So sulphur dioxide is a gas and a polar molecule at room temperature.

Neither of these meet the criteria in the question, so answer A is not correct. KBr or potassium bromide is an ionic solid at room temperature and pressure. In the giant ionic lattice, the positive and negative charges balance each other out. KBr is neither a liquid at room temperature, nor can it be described as polar or nonpolar due to its giant ionic structure. Answer B is not correct. CF₄ or carbon tetra fluoride is a gas at room temperature. CF₄ is a nonpolar molecule due to its symmetrical shape. However, the fact that it’s a gas at room temperature means it’s not the correct answer here. Answer C is not correct.

HCl or hydrogen chloride is also a gas at room temperature. It’s also a polar molecule. Neither of these meet the criteria in the question. D is not the correct answer. Finally, we have C₆H₆ or benzene. This is a liquid at room temperature. Benzene contains carbon to carbon and carbon to hydrogen covalent bonds only. None of these bonds are polarized. Therefore, benzene is a nonpolar molecule. We have found our nonpolar liquid. And answer E is the correct answer.

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