Video: Identifying the Arrows That Indicate Losing and Gaining Electrons in Redox Reactions

Consider the equation shown. Cl₂ (aq) + 2Br⁻ (aq) ⟶ Br₂ (aq) + 2Cl⁻ (aq). a) Which arrow shows reduction? b) Which arrow involves a loss of electrons? c) Which arrow involves the gain of electrons?

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Video Transcript

Consider the equation shown. Cl2 aqueous plus 2Br− aqueous react to form Br2 aqueous plus 2Cl− aqueous. (a) Which arrow shows reduction? (b) Which arrow involves a loss of electrons? And (c) which arrow involves the gain of electrons?

The arrow in all three questions refers to either A or B. In the equation, we can see the chlorine molecule Cl2 reacting with the bromide ion Br−, forming bromine Br2, which dissolves readily in water producing a memorable orange color, and chloride ions Cl−. To make it easier, you can separate the individual processes. So A refers to Cl2 transforming into two Cl− and process B refers to two Br− transforming into Br2. Here, I’m ignoring the state symbols.

In process A, we see a molecule of chlorine composed of two chlorine atoms, transforming into two chloride ions, each with a charge of one minus. Therefore, this process reflects the addition of two electrons, one to each of the chlorine atoms. And for B, we have two negatively charged bromide ions, transforming into neutral bromine atoms in a bromine molecule. Therefore, B corresponds to the process of removing two electrons.

Question (a) refers to reduction. Reduction is the process of gaining electrons. This is easy to remember if we use OIL RIG. Oxidation is loss; reduction is gain of electrons. Therefore, the answer to part (a) is arrow A. In arrow A, chlorine is being transformed to chloride by the addition of electrons. This is reduction.

Part (b) asks us to indicate the arrow that involves a loss of electrons. This is arrow B. In process B, we have two bromide ions being transformed into bromine, losing two electrons. And finally, the answer to part (c) is arrow A. In reaction A, chlorine is gaining electrons to form chloride.

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