Video Transcript
Select the statement that does not accurately describe the following chemical reaction. Hydrated Na2CO3 solid reversibly produces Na2CO3 solid plus 10 H2O gas. (A) Anhydrous sodium carbonate is produced. (B) The forward reaction is endothermic. (C) The reaction is reversible. (D) Blue crystals are formed. (E) H2O gas is formed.
This question is asking us to select the answer choice that does not accurately describe the reaction. In other words, four of the answer choices will be true statements about this reaction. The correct answer will be the one answer choice that is a false statement. We can cancel out several of the answer choices just by looking at the written equation.
First, we can see that H2O in the gaseous state is indeed a product of this reaction. Since choice (E) is a true statement, it is not the correct answer for this problem. Next, the double-headed arrow in the middle of this equation signifies that it is a reversible reaction. Therefore, we can eliminate the true statement in choice (C) from consideration. This reaction does indeed occur in both directions. We can dehydrate the hydrated salt or we can rehydrate the anhydrous salt.
That brings us to the next incorrect answer choice, answer choice (A). The reactant in this equation is hydrated sodium carbonate. The middle dot followed by a certain number of water molecules represents what we call water of crystallization. These are water molecules that are trapped in the lattice structure of the ionic compound. A salt with water of crystallization is a hydrated salt. When we remove the water from this structure, however, it becomes anhydrous sodium carbonate, anhydrous meaning there is no water of crystallization in the compound. Since anhydrous sodium carbonate is indeed produced in this reaction, we can eliminate choice (A) from consideration.
One important piece of information to consider is that for dehydration reactions like this one, heat is added and absorbed in order to dehydrate the salt. A reaction where the system absorbs heat is called an endothermic reaction. Since the forward reaction, the one that goes from left to right, is indeed endothermic, we can eliminate choice (B) from consideration. We have only one answer choice remaining: blue crystals are formed. Let’s confirm that this is an incorrect statement. As it turns out, anhydrous sodium carbonate is a white substance, not blue. Since choice (D) is indeed a false statement, we can confirm that it is the correct answer to this problem.
So, which statement does not accurately describe the following chemical reaction? That’s choice (D) blue crystals are formed.
