2.4. Salts

Write the chemical formulae of the salts given below: Potassium sulphate, sodium sulphate, calcium sulphate, magnesium sulphate, copper sulphate, sodium chloride, sodium nitrate, sodium carbonate and ammonium chloride.

Identify the acids and bases from which the above salts may be obtained.

Salts having the same positive or negative radicals are said to belong to a family. For example, NaCl and Na2SO4 belong to the family of sodium salts. Similarly, NaCl and KCl belong to the family of chloride salts. How many families can you identify among the salts given in this Activity?

In this section, we learn about salts and how they can be categorized into families based on common radical components. Salts are ionic compounds formed from the reaction of acids and bases. Each type of salt can be derived from specific acids and bases. Identifying the chemical formulae of various salts helps us understand their composition and how they relate to their parent acid or base. For example, sodium chloride (NaCl) is derived from hydrochloric acid (HCl) and sodium hydroxide (NaOH). Furthermore, salts that share the same cation or anion are grouped into families. For instance, sodium sulfate (Na2SO4) and sodium chloride (NaCl) both belong to the sodium family, showcasing how compounds can belong to the same category despite not being identical.

Think of a family reunion where every attendee shares a common last name, like ‘Smith’. Just as ‘Smith’ connects people from various backgrounds but keeps them in one family, the chemical formulae of salts connect different compounds into families sharing common components. This action helps chemists quickly determine the relationships and similarities between different salts, akin to recognizing family traits among relatives.

Collect the following salt samples – sodium chloride, potassium nitrate, aluminium chloride, zinc sulphate, copper sulphate, sodium acetate, sodium carbonate and sodium hydrogencarbonate (some other salts available can also be taken).

Check their solubility in water (use distilled water only).

Check the action of these solutions on litmus and find the pH using a pH paper.

Which of the salts are acidic, basic or neutral?

Identify the acid or base used to form the salt.

Report your observations in Table 2.4.

Salts of a strong acid and a strong base are neutral with pH value of 7. On the other hand, salts of a strong acid and weak base are acidic with pH value less than 7 and those of a strong base and weak acid are basic in nature, with pH value more than 7.

This chunk discusses how to determine the pH levels of various salts, shedding light on their acidic or basic nature. When salts dissolve in water, they can either release H+ ions (making the solution acidic), OH- ions (making it basic), or neither (making it neutral). For example, sodium chloride (a product from strong acid and strong base) will not affect the pH much, whereas ammonium chloride (from a strong acid and weak base) will make the solution acidic. The pH levels can indicate the salt's interaction with water, revealing whether it's beneficial for certain applications like agriculture or food processing.

Imagine a sports team where players have different strengths. A strong player may excel in offense (basic) while another specializes in defense (acidic). When combined, the team’s overall performance can shift to a neutral effectiveness, depending on the players' strengths and weaknesses. Similarly, when mixed in water, certain salts can create an acidic, basic, or neutral environment based on their inherent properties, affecting how they interact in various applications.

By now you have learnt that the salt formed by the combination of hydrochloric acid and sodium hydroxide solution is called sodium chloride. This is the salt that you use in food.

You must have observed in the above Activity that it is a neutral salt.

Seawater contains many salts dissolved in it. Sodium chloride is separated from these salts. Deposits of solid salt are also found in several parts of the world. These large crystals are often brown due to impurities. This is called rock salt. Beds of rock salt were formed when seas of bygone ages dried up.

The common salt thus obtained is an important raw material for various materials of daily use, such as sodium hydroxide, baking soda, washing soda, bleaching powder and many more.

In this segment, we explore sodium chloride more closely and its importance as a common salt in our daily lives. Sodium chloride not only enhances flavor in foods but also acts as a base ingredient in the production of various chemicals used in households and industries. The process of extracting it from seawater or rock deposits illustrates its abundance and versatility. As a neutral salt, it does not significantly alter the pH when dissolved in water, which is advantageous for culinary and chemical uses. The mention of other products, such as baking soda and washing soda, shows the role sodium chloride plays in the synthesis of compounds essential for cleaning, cooking, and many other daily activities.

Think of sodium chloride as a universal ingredient in a kitchen, essential for prepping a meal, much like how a recipe hinges on salt to elevate flavors. Beyond just seasoning, rock salt found in nature is like the rawest form of this important ingredient, illustrating how nature provides for our needs. Additionally, just like flour can be transformed into bread, sodium chloride transforms into various essential substances, highlighting its versatility in our daily life.

Heat a few crystals of copper sulphate in a dry boiling tube.

What is the colour of the copper sulphate after heating?

Do you notice water droplets in the boiling tube? Where have these come from?

Add 2-3 drops of water on the sample of copper sulphate obtained after heating.

What do you observe? Is the blue colour of copper sulphate restored?

Water of crystallisation is the fixed number of water molecules present in one formula unit of a salt.

This chunk focuses on the phenomenon known as water of crystallisation, which refers to the specific number of water molecules associated with crystal formations of certain salts, such as copper sulphate. When heated, copper sulphate loses its color and turns white, indicating the loss of these water molecules. The subsequent addition of water restores its blue color, demonstrating that the water was initially a part of the crystal structure. Understanding this concept is crucial for recognizing how certain salts behave under varying conditions and how they can be modified for different uses in industries.

Imagine a sponge soaking up water. Just as the sponge expands and changes appearance when water is added, salts like copper sulphate change color when they absorb or lose water. This ability to hold water is essential in various applications, such as in agriculture for soil management, where water retention influences crop growth.

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