Problem 3 - Chemistry in 30 days

Question

Barium chloride is treated with potassium chromate. A ppt. is observod. What is the colour 7 (a) yellow (b) green (c) white (d) flesh

Step-by-Step Solution

Answer

The precipitate formed is yellow, so the answer is (a) yellow.

Step 1: Identify the Reaction

When barium chloride (BaCl extsubscript{2}) reacts with potassium chromate (K extsubscript{2}CrO extsubscript{4}), a double displacement reaction occurs. The chemical equation for this reaction is: \[\text{BaCl}_2 (aq) + \text{K}_2\text{CrO}_4 (aq) \rightarrow \text{BaCrO}_4 (s) + 2\text{KCl} (aq)\]Barium chromate (BaCrO extsubscript{4}) is the solid precipitate formed during this reaction.

Step 2: Determine the Precipitate's Color

Barium chromate (BaCrO extsubscript{4}) is known for its distinct color. The precipitate of barium chromate is characterized by a bright yellow color.

Step 3: Select the Correct Option

Based on the color identification of the precipitate, the correct answer for the precipitate's color is 'yellow.' Therefore, the correct option is (a) yellow.

Key Concepts

Double Displacement Reaction

In a double displacement reaction, also known as a metathesis reaction, two compounds exchange ions to form two new compounds. This type of reaction is common in solutions where the ions are free to move. Barium chloride reacting with potassium chromate is a classic example. Here, the ions switch places, leading to the formation of barium chromate and potassium chloride.

• The formula for barium chloride is \( \text{BaCl}_2 \).
• Potassium chromate is represented as \( \text{K}_2\text{CrO}_4 \).
• These react to form barium chromate \( \text{BaCrO}_4 \) and potassium chloride \( \text{KCl} \).

During this reaction, barium (Ba) pairs with chromate (CrO₄) to form a new compound, barium chromate. Meanwhile, potassium (K) pairs with chloride (Cl) to form potassium chloride in the solution phase.

Chemical Equation

Writing a chemical equation correctly is crucial to understanding the relationship between reactants and products. In the reaction between barium chloride and potassium chromate, the chemical equation is written as:\[\text{BaCl}_2 (aq) + \text{K}_2\text{CrO}_4 (aq) \rightarrow \text{BaCrO}_4 (s) + 2\text{KCl} (aq)\]This equation provides specific insights into the reaction:

• "(aq)" indicates that both barium chloride and potassium chromate are in aqueous solutions.
• "(s)" signifies that barium chromate is a solid, specifically a precipitate.
• Each atom is balanced across both sides of the equation, which follows the law of conservation of mass.

A well-written chemical equation not only helps in predicting the products but also in understanding the stoichiometry of the reaction, including how many moles of each reactant are needed to form the product.

Precipitate Color Identification

Identifying the color of a precipitate is an essential skill in chemistry, as it can help in the identification of compounds formed during a reaction. In this case, barium chromate \( \text{BaCrO}_4 \) forms a bright yellow precipitate. This is a signature characteristic of barium chromate and can be used as an indicator of its formation.

• The term "precipitate" describes a solid formed in a solution as a result of a chemical reaction.
• The color "yellow" is distinct and helps quickly identify barium chromate compared to other potential products.
• This color knowledge ensures chemists understand what product has formed without needing complex analysis.

Knowing the color of common precipitates is valuable for experimental work, particularly in qualitative analysis, where visual identification of compounds is often the first step in analyzing a reaction's outcome.