Uses of salts Notes

How Do Properties of Salts Make Them Useful or Hazardous?

Salts are not all the same. Their properties determine whether they are helpful, harmful, or both:

1. Solubility – how well they dissolve in water.
2. Hygroscopicity – ability to absorb water from the air.
3. Toxicity – how harmful they are to living organisms.

Solubility

Highly Soluble Salts

1. Example: Sodium chloride, NaCl
   1. Dissolves easily in water.
   2. Forms ions that move freely → important for electrolyte solutions and de-icing roads.
2. Advantages:
   1. Easy to dissolve and spread.
   2. Cheap and widely available.
3. Risks:
   1. Runoff can increase soil and water salinity, harming plants and aquatic life.
   2. Corrodes metal structures (cars, bridges).

Low-Solubility Salts

1. Example: Barium sulfate, BaSO₄
   1. Very poorly soluble in water.
   2. Because it does not dissolve, it is not absorbed by the body.
2. Advantages:
   1. Good contrast agent for imaging.
   2. Passes through the body without entering the bloodstream.
3. Risks:
   1. If a soluble barium salt were used by mistake, it would be highly toxic.
   2. Must be used only under medical supervision.

Ability to Absorb Water (Hygroscopicity)

Some salts can absorb water from the air; some even form hydrated crystals or turn into a solution.

Desiccants (Drying Agents)

1. Examples: Calcium chloride (CaCl₂), magnesium sulfate (MgSO₄)
   1. Used to keep things dry by absorbing moisture from their surroundings.
   2. Often found in small sachets in electronics, shoe boxes, medicine bottles.
2. Advantages:
   1. Prevents corrosion, mould and spoilage.
   2. Useful in packaging, laboratories, and industry.
3. Risks:
   1. Can cause corrosion if they release absorbed water in the wrong place.
   2. Some can cause skin and eye irritation – handle with care and avoid ingestion.

Toxicity

Not all salts are safe. Some are essential nutrients; others are highly toxic.

Beneficial Salts

Examples:

1. Potassium chloride (KCl) – used in fertilisers to provide potassium, an essential nutrient for plants.
2. Sodium chloride (NaCl) – needed in small amounts in our diet to regulate fluid balance and nerve function.

Toxic or Hazardous Salts

1. Examples:
   1. Mercury(II) chloride, HgCl₂ – highly toxic; can damage the nervous system and organs.
   2. Lead(II) nitrate, Pb(NO₃)₂ – toxic; exposure can cause serious health problems, especially in children (brain and developmental issues).
2. Risks:
   1. Can contaminate water and soil.
   2. Can enter the food chain, accumulating in organisms.

How Are Salts Used in Food, Agriculture and Medicine?

Because of their varied properties, salts are used in many areas of everyday life.

Food Preservation

1. Main salt used: Sodium chloride (NaCl)
   1. Used to preserve food by drawing water out of microbial cells by osmosis.
   2. Less water → bacteria and fungi cannot grow easily.
2. Examples:
   1. Salting meat or fish to prevent spoilage.
   2. Pickling vegetables in brine.
3. Benefits:
   1. Extends shelf life.
   2. Reduces food waste.
   3. Traditional and low-cost method.
4. Health considerations:
   1. Our bodies need some salt.
   2. Too much dietary NaCl can contribute to high blood pressure (hypertension) and cardiovascular disease.

Agriculture

Fertilisers

1. Examples:
   1. Potassium chloride (KCl) – supplies potassium for plant growth.
   2. Ammonium nitrate (NH₄NO₃) – supplies nitrogen, important for leaf and stem growth.
2. Benefits:
   1. Boosts crop yield.
   2. Helps feed a growing global population.
3. Risks:
   1. Overuse can lead to soil salinity and nutrient imbalance.
   2. Nitrate can leach into water, contributing to eutrophication (algal blooms) in lakes and rivers.

Soil Conditioning

1. Example: Gypsum (CaSO₄·2H₂O)
   1. Improves soil structure by helping clay particles clump together.
   2. Helps reduce soil salinity and improve drainage.
2. Benefits:
   1. Better root growth.
   2. Improved crop health.

Medicine

Electrolyte Solutions

Examples: NaCl, KCl, other balanced salt solutions

1. Used in intravenous (IV) fluids to restore or maintain electrolyte balance.
2. Important during dehydration, surgery, or illness.

Epsom Salt (Magnesium sulfate, MgSO₄)

1. Used in baths to relieve muscle pain and inflammation.
2. Used medicinally as a laxative in controlled doses.
3. Benefits:
   1. Supports essential body functions (nerve impulses, muscle contraction).
   2. Can aid recovery and comfort.
4. Risks:
   1. Incorrect concentration or uncontrolled self-medication can be harmful.
   2. IV solutions must be carefully formulated and administered by professionals.

How Do We Assess the Benefits and Risks of Using Salts?

To evaluate a salt’s use, we need to consider several perspectives:

1. Environmental impact
2. Health risks
3. Economic cost
4. Ethical and regulatory factors

Environmental Impact

Soil Salinity

1. Excessive use of salts (NaCl, KCl) can build up in soil.
2. High salt levels make it harder for plants to take up water → reduced growth and yield.

Water Pollution

1. Salts from de-icing and fertilisers can wash into rivers and lakes.
2. Increased salinity can stress or kill freshwater organisms (fish, amphibians, invertebrates).

Health Risks

Toxic Salts

1. Salts of heavy metals (e.g. lead, mercury, cadmium) can cause serious health problems:
   1. Nervous system damage
   2. Kidney/liver damage
   3. Developmental issues in children
2. These must be:
   1. Carefully controlled in industry.
   2. Stored, handled and disposed of safely.

Dietary Salt

1. NaCl is essential in small amounts.
2. Too much in the diet is linked to hypertension and heart disease.

Economic Considerations

1. NaCl is cheap and widely available → attractive for de-icing and food preservation.
2. More environmentally friendly alternatives (like CMA) are more expensive.
3. Trade-off:
   1. Cheaper salts may have higher environmental costs.
   2. Greener alternatives may be less affordable for large-scale use.

Ethical and Regulatory Considerations

1. Governments may ban or restrict toxic salts (e.g. lead-based salts) to protect public health.
2. Industry has an ethical responsibility to:
   1. Use salts in ways that minimise harm.
   2. Comply with environmental regulations.
   3. Invest in safer alternatives and proper waste management.