Which of the following choices represents the types of precipitation reactions in the chemical analysis technique? (A) Flame tests and gravimetric methods. (B) Flame tests and volumetric methods. (C) Gravimetric methods and volumetric methods. (D) Spot tests and gravimetric methods. Or (E) spot tests and volumetric methods.
Chemical analysis is used to identify and quantify the substances in a material or mixture. There are many ways to analyze the content and composition of a chemical sample. We’ve been given four different types of analysis methods, from options (A) to (E). A flame test involves a Bunsen burner flame changing color in the presence of certain ions. The color that the flame turns can be used to identify these ions. So the flame test is used to identify substances and so is a chemical analysis technique. But the question asks which of the following choices represents the type of precipitation reactions in the chemical analysis technique.
A precipitation reaction is a reaction which forms an insoluble solid product from the reaction between two soluble substances in solution. The flame test only involves ions changing the color of a flame, so it does not involve a precipitation reaction. Thus, neither of the options that contain flame tests is correct. So neither option (A) or option (B) can be the correct answer to this question.
Gravimetric methods or gravimetric analysis involves using various methods to quantify an analyte based on its mass. The mass that is analyzed is often the mass of a precipitate. So gravimetric analysis does involve precipitation reactions. Thus, option (C) and option (D) may be the answer to the question. We can even define precipitation gravimetry as an analytical technique that uses the formation and mass of a precipitate to determine the mass of an analyte.
Volumetric methods or volumetric analysis is where the amount of a substance is determined by measuring its volume or by measuring the volume of a second substance that reacts with it. An example of this would be a titration. So volumetric methods or volumetric analysis involves measuring the volume of a liquid, thus doesn’t involve precipitation. Thus, neither of the remaining answer choices (C) and (E) that contain volumetric methods can be the answer to the question. By process of elimination, we can see that option (D), spot tests and gravimetric methods, is the answer to this question. But for completeness, let’s look at spot tests.
Spot tests involve a drop or a few drops of chemical reagent being added to a drop of an unknown mixture. A positive spot test involves the reaction between substances, often forming a precipitate. This confirms that the answer to the question “Which choice represents the types of precipitation reactions in the chemical analysis technique?” is (D) spot tests and gravimetric methods.