A solid is known to be either BaCO3 or CaCO3. It is dissolved in 6 M acetic acid. A pale yellow precipitate forms when K2CrO4 solution is added. The subsequent flame test with that precipitate shows an orange-red color. Which cation is present? Briefly explain
solid is known to be either BaCO3 or CaCO3. It is dissolved in 6 M acetic acid. A pale yellow precipitate forms when K2CrO4 solution is added. The subsequent flame test with that precipitate shows an orange-red color. Which cation is present? Briefly explain
Using the results of the flame test would indicate that the precipitate is Ca2+. Although the color of the precipitate after the addition of K2CrO4 is the pale yellow of BaCrO4, that is only a superficial indication. CaCro4 is also yellow and may precipitate, particularly if the pH is high. A further test (the flame test in this case) is needed to confirm which cation is present, which in this case is Ca2+.
Based on the given information, we can determine the cation present by following these steps:
Step 1: Concerning the formation of a pale yellow precipitate when K2CrO4 solution is added, we know that K2CrO4 is a yellow solution. Therefore, the formation of a pale yellow precipitate indicates the presence of a cation that reacts with chromate ions (CrO4^2-) to form an insoluble salt.
Step 2: The subsequent flame test indicates that the cation present produces an orange-red color in the flame. Flame tests are used to identify certain metal ions based on the characteristic color they emit when heated in a flame.
Considering these observations, we can conclude that the cation present in the solid is Ba^2+ (barium). When barium ions react with chromate ions, it forms the insoluble salt BaCrO4, which appears as a pale yellow precipitate. Additionally, when barium is heated in a flame, it produces an orange-red color.
Therefore, by analyzing the reactions and the flame test color, we can determine that the cation present is Ba^2+ (barium).
To determine which cation is present, we need to analyze the information provided step by step:
1. Reaction with Acetic Acid: Both BaCO3 (barium carbonate) and CaCO3 (calcium carbonate) react with acetic acid (CH3COOH). The reaction can be represented as follows:
BaCO3 + 2CH3COOH → Ba(CH3COO)2 + H2O + CO2
CaCO3 + 2CH3COOH → Ca(CH3COO)2 + H2O + CO2
Both reactions result in the formation of acetates and the evolution of carbon dioxide gas.
2. Formation of a Pale Yellow Precipitate: When K2CrO4 (potassium chromate) solution is added to the resulting solution from the previous step, a pale yellow precipitate forms. This indicates the presence of an insoluble chromate compound.
3. Flame Test: The flame test is used to identify cations based on the characteristic colors they produce when heated in a flame. In this case, the precipitate is subjected to the flame test and shows an orange-red color.
Based on the given observations, we can conclude that the cation present is barium (Ba2+). This is because barium forms an insoluble chromate compound (BaCrO4), which gives an orange-red flame color.
In summary, the cation present in the solid is barium (Ba2+) based on the formation of a pale yellow precipitate with K2CrO4 solution and the subsequent orange-red flame test.