Video: Identifying the Best Description of the Reaction of Sodium Carbonate and Calcium Chloride Solutions in a Set of Descriptions

Which of the following best describes the reaction of sodium carbonate and calcium chloride solutions? [A] Fusion [B] Precipitation [C] Nuclear transformation [D] Combustion [E] Reduction

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Video Transcript

Which of the following best describes the reaction of sodium carbonate and calcium chloride solutions? A) Fusion, B) precipitation, C) nuclear transformation, D) combustion, or E) reduction.

So we’re looking at the reaction of sodium carbonate and calcium chloride. The symbol for sodium carbonate is Na₂CO₃. Remember, the carbonate anion has a two minus charge. So we need two sodium ions to counterbalance that charge. The symbol for calcium chloride is CaCl₂. In this case, we need two of the singly charged chloride ions to counterbalance the two positive charge of the calcium cation.

The question tells us we’re taking solutions of these two materials and reacting them together. When we do this, our products are calcium carbonate and sodium chloride. Calcium carbonate is insoluble. So we would see it emerge as a solid. If we mix solutions of these two in the lab, we’d likely see a fine powder of calcium carbonate form, turning the solution cloudy. The sodium chloride, being highly soluble, would remain in solution and not affect its color.

So, back to the question, which of the five types of reaction mentioned best describes the reaction of our two solutions? The word fusion is rarely used to describe chemical reactions. It’s much more common to see it describing nuclear reactions, as in nuclear fusion. You might see this type of reaction in the sun, where hydrogen nuclei fuse together to form helium nuclei. In the reaction of sodium carbonate and calcium chloride, we don’t see any elements changing identity or fusing together. So we don’t call this a fusion reaction.

However, a precipitation reaction is one where we produce a solid from solution. In the reaction of sodium carbonate and calcium chloride, we’re going from all components being dissolved, so a solution, to a mixture involving a solid. So precipitation is a pretty good description of this reaction. However, we should be careful because the question says which of the following best describes the reaction. So there’s a chance that one of the other descriptions could apply and be a better description.

A nuclear transformation reaction is one where we see a change in the composition of nuclei. So in a nuclear transformation process, we would expect the number of protons or neutrons in some of the nuclei to change. An example of a nuclear transformation is any decay where we produce a beta particle, for instance, the decay of thorium 234 to protactinium 234. In this process, a neutron in the nucleus of the thorium isotope transforms into a proton, changing the identity of the nucleus from a thorium nucleus into a protactinium nucleus. In our reaction, sodium carbonate plus calcium chloride, all the nuclei retain their original identities. The sodium nuclei are still sodium nuclei. The carbon nuclei are still carbon nuclei and so on. So we’re not dealing with a nuclear transformation.

The next candidate, combustion, means reaction with oxygen, O₂. We do have oxygen present in the carbonate anion. But it’s not present in the form of O₂. And the oxygen doesn’t change its form from one side of the reaction to the other. So we’re not dealing with a combustion reaction. Finally, in a reduction reaction, we’ll see the oxidation state of one or more components reduce. This might happen, for instance, due to the direct gaining of electrons.

The oxidation state of sodium in the starting materials is positive one. And its oxidation state does not change because of the reaction. The same is true for carbon, which retains its positive four oxidation state. Oxygen stays constant at negative two, calciums at positive two, and chlorines at negative one. So this reaction cannot be a reduction reaction because the oxidation states of each component remains the same.

Therefore, of the five descriptions given, the one that best describes the reaction of sodium carbonate and calcium chloride solutions is precipitation.

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