QUESTION NO 5

(a) How does Tin react with NaOH (aqueous), HgCl, solution and HNO₂?

Tin (Sn) reacts differently with various chemicals. Here’s how it reacts with aqueous sodium hydroxide (NaOH), mercuric chloride (HgCl₂), and nitrous acid (HNO₂):

1. Reaction with Aqueous Sodium Hydroxide (NaOH):
   Tin reacts with aqueous NaOH to form sodium stannate and hydrogen gas. The reaction can be represented as: [ \text{Sn} + 2\text{NaOH} + 2\text{H}_2\text{O} \rightarrow \text{Na}_2\text{SnO}_2 + 2\text{H}_2 ] Here, tin (Sn) reacts with sodium hydroxide (NaOH) in the presence of water to form sodium stannate ((\text{Na}_2\text{SnO}_2)) and hydrogen gas ((\text{H}_2)).
2. Reaction with Mercuric Chloride (HgCl₂):
   Tin reacts with mercuric chloride to form mercurous chloride (Hg₂Cl₂) and tin(II) chloride (SnCl₂). The reaction is: [ \text{Sn} + 2\text{HgCl}_2 \rightarrow \text{SnCl}_2 + \text{Hg}_2\text{Cl}_2 ] Here, tin (Sn) reduces mercuric chloride (HgCl₂) to mercurous chloride (Hg₂Cl₂) and is itself oxidized to tin(II) chloride (SnCl₂).
3. Reaction with Nitrous Acid (HNO₂):
   Tin reacts with nitrous acid to form stannous nitrite and water. The reaction is: [ \text{Sn} + 2\text{HNO}_2 \rightarrow \text{Sn(NO}_2)_2 + 2\text{H}_2\text{O} ] In this reaction, tin (Sn) reacts with nitrous acid (HNO₂) to form stannous nitrite ((\text{Sn(NO}_2)_2)) and water ((\text{H}_2\text{O})).

These reactions illustrate tin’s ability to act as a reducing agent and its interaction with different reagents.

(b) How does Tin occur in nature?

Tin occurs in nature primarily in the form of its ores. The two main minerals in which tin is found are:

1. Cassiterite (SnO₂): This is the most important and widely used tin ore. Cassiterite is a heavy, black or brown mineral that contains about 78.8% tin by weight. It is the primary source of tin and is found in alluvial deposits and in hard rock deposits.
2. Stannite (Cu₂FeSnS₄): This is a less common tin ore. Stannite is a sulfide mineral that contains tin, copper, iron, and sulfur. It is found in some hydrothermal deposits and is less important as a tin source compared to cassiterite.

Occurrence:

• Alluvial Deposits: Tin is often found in alluvial deposits, where cassiterite has been eroded from its primary source and accumulated in riverbeds, streams, and sedimentary deposits.
• Hard Rock Deposits: Cassiterite can also be found in primary deposits associated with granite and other igneous rocks. These deposits are mined through hard rock mining techniques.
• Hydrothermal Deposits: Stannite is found in hydrothermal veins, often associated with other sulfide minerals.

Geographical Locations:

Tin deposits are found in various parts of the world, including:

• China: One of the largest producers of tin, with significant deposits in the Yunnan province.
• Indonesia: Known for its large alluvial tin deposits, particularly in the islands of Bangka and Belitung.
• Myanmar (Burma): Another major producer, with important deposits in the Kachin state.
• Malaysia: Historically a significant producer of tin from alluvial deposits.
• Brazil: Contains substantial hard rock deposits of cassiterite.

These deposits are exploited through both mining and geological exploration, contributing to the global supply of tin.

(c) Describe extraction of Tin from an important ore.

The extraction of tin from its principal ore, cassiterite (SnO₂), involves several steps including mining, concentration, and refining. Here’s a detailed description of the process:

1. Mining:

• Alluvial Mining: Cassiterite often occurs in alluvial deposits. In this method, the ore is extracted from riverbeds or stream beds using various techniques like dredging, panning, or sluicing.
• Hard Rock Mining: Cassiterite is also mined from primary deposits in hard rock formations. This involves traditional mining techniques such as drilling and blasting to extract the ore.

2. Concentration:

• Crushing and Grinding: The mined ore is first crushed and ground to liberate the cassiterite particles from the surrounding rock.
• Gravity Separation: Cassiterite is a heavy mineral, so it can be concentrated using gravity separation techniques. This often involves shaking tables, jigs, or spiral concentrators to separate the dense cassiterite from the lighter gangue materials.
• Washing and Screening: Additional washing and screening may be used to remove impurities and improve the purity of the concentrate.

3. Extraction and Refining:

• Roasting: The concentrated ore (cassiterite) is roasted in the presence of oxygen to convert any impurities and to prepare it for further processing. During roasting, impurities such as sulfur and arsenic are removed as gases. [
  \text{SnO}_2 + \text{O}_2 \rightarrow \text{SnO}_2
  ]
• Reduction: The purified cassiterite is then reduced to obtain tin metal. This is typically done in a furnace using a reducing agent such as carbon (in the form of coke) or hydrogen. The reduction process involves heating the ore with the reducing agent to convert tin dioxide (SnO₂) to tin metal (Sn). [
  \text{SnO}_2 + 2\text{C} \rightarrow \text{Sn} + 2\text{CO}
  ] or [
  \text{SnO}_2 + 2\text{H}_2 \rightarrow \text{Sn} + 2\text{H}_2\text{O}
  ]
• Refining: The tin obtained from the reduction process may still contain impurities. It is further refined using methods such as electrolysis or chemical treatments to produce high-purity tin. Electrolytic refining involves dissolving the tin in a suitable electrolyte and then depositing it on a cathode to achieve a high level of purity.
• Alloying (if required): For some applications, tin is alloyed with other metals, such as lead to produce solder or bronze with copper.

The end product is high-purity tin metal, which is used in various applications such as soldering, coating for steel cans, and in the manufacture of bronze.