GED Science TestPhysical ScienceMedium
A chemist is analyzing an unknown solution and adds a small amount of a strong acid. They observe a rapid decrease in pH and the solution begins to fizz vigorously, producing a gas. This observation is strong evidence of which type of chemical reaction?
- AAcid-carbonate reaction
- BRedox reaction
- CPrecipitation reaction
- DAcid-base neutralization reaction
Show answer & explanationAnswer & explanation
Correct answer: A. Acid-carbonate reaction
The fizzing and production of a gas upon adding an acid, along with a pH decrease, is characteristic of an acid reacting with a carbonate (like calcium carbonate). This reaction produces carbon dioxide gas, which causes fizzing.
Why the other options are wrong
- B. A redox reaction involves electron transfer, but fizzing is not a direct indicator of it in this context.
- C. A precipitation reaction forms an insoluble solid (precipitate), not necessarily fizzing gas.
- D. An acid-base neutralization reaction produces salt and water, and while pH changes, fizzing gas is not a typical indicator unless a carbonate is involved.
Acid-Carbonate Reaction
A chemical reaction between an acid and a carbonate compound, typically producing a salt, water, and carbon dioxide gas.
- Characteristic fizzing/effervescence (CO2 gas)
- Example: HCl + CaCO3 → CaCl2 + H2O + CO2
- Used to test for carbonates
Memory trick: Fizzy gas from acid means carbonate's past.