In the extraction of silver by Mac-arther cyanide process, a small of `KNO_(3)` is also added as a flux. The function of `KNO_(3)` is:

Options

A. to oxidise Ag in the native form to `Ag^(+)`
B. to oxidise lead and zinc impurities
C. to form a complec with `Ag^(+)` which is then reduced to metallic silver by using zinc
D. to oxidise the sulphur in the argentite ore to `SO_(2)` which escapes from the reaction

Answer

To solve the question regarding the role of KNO3 in the extraction of silver by the MacArthur cyanide process, we can break down the solution into the following steps:

### Step 1: Understand the MacArthur Cyanide Process
The MacArthur cyanide process is a method used for extracting silver from its ore, particularly from silver sulfide (Ag2S). The process involves several steps, including the concentration of the ore, leaching with cyanide, and reduction to obtain metallic silver.

**Hint:** Familiarize yourself with the overall process of silver extraction to understand where KNO3 fits in.

### Step 2: Identify the Role of KNO3
In the context of the extraction process, KNO3 is added as a flux. A flux is a substance that helps to remove impurities during the metallurgical process.

**Hint:** Think about what impurities might be present in the ore and how a flux could assist in their removal.

### Step 3: Determine the Impurities in the Ore
The ore used in the MacArthur process often contains impurities such as lead (Pb) and zinc (Zn). These impurities can interfere with the extraction of silver.

**Hint:** Consider the common impurities found in silver ores and how they might affect the extraction process.

### Step 4: Explain the Function of KNO3
KNO3 acts as an oxidizing agent in the process. It helps to oxidize the lead and zinc impurities present in the ore, converting them into forms that can be easily removed. This is crucial for ensuring that the extraction of silver is efficient and that the final product is of high purity.

**Hint:** Reflect on the chemical reactions that might occur when KNO3 is introduced to the ore and how these reactions facilitate impurity removal.

### Step 5: Conclusion
The primary function of KNO3 in the MacArthur cyanide process is to oxidize lead and zinc impurities, allowing for their removal and thus enhancing the purity of the extracted silver.

**Final Answer:** The function of KNO3 is to oxidize lead and zinc impurities present in the silver ore.