When an old building is to be torn down, Mr. Pham’s company removes the bricks, cleans off the mortar from the bricks, and then sells the bricks to companies that restore historic buildings. Which compound is Mr. Pham’s company most likely to use in its work?

Mortar contains calcium compounds, including calcium carbonate, which reacts with acid and can be loosened from the bricks. Hydrochloric acid is commonly used to remove mortar residue; sodium hydroxide and lithium hydroxide are bases, so they are not suitable for this task. The best choice is hydrochloric acid.

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