The presence of certain metal ions in small amounts is beneficial to living organisms because they act as cofactors for enzymes or play structural roles in biological molecules. These ions are often essential for proper physiological function.

Example 1: Zinc (Zn) is a crucial cofactor for many enzymes involved in growth, development, and immune function. It is also important for wound healing and maintaining a healthy sense of taste and smell.

Source in the diet: Red meat, shellfish (oysters), poultry, beans, nuts, and whole grains.

Example 2: Iodine (I) is essential for the production of thyroid hormones, which regulate metabolism, growth, and development. Thyroid hormones are vital for brain development in infants and children.

Source in the diet: Iodized salt, seafood (fish, seaweed), dairy products, and eggs.

Without sufficient amounts of these metal ions, various physiological processes can be impaired, leading to health problems. Therefore, obtaining adequate amounts of these essential trace elements through the diet is important for maintaining health.

To assess the purity of water using melting and boiling point, a student would follow these steps:

Melting Point Test:

• Apparatus: Melting point apparatus (including a melting point tube, thermometer, clamp, and stand), a water sample, and a weighing balance.
• Procedure:

  • Accurately weigh a small amount of the water sample into the melting point tube.
  • Clamp the melting point tube in the melting point apparatus.
  • Slowly heat the water sample, observing the temperature.
  • Record the temperature at which the water begins to melt and the temperature at which it is completely melted.

• Interpretation: Pure water has a sharp melting point of 0°C. Impurities will depress and broaden the melting point range. A depressed melting point indicates the presence of dissolved substances. The extent of depression is related to the amount of impurity. A broad melting point range suggests significant impurities.

Boiling Point Test:

• Apparatus: A boiling tube, a thermometer, a Bunsen burner, a tripod, and a wire gauze.
• Procedure:

  • Set up the boiling tube in the water bath using a tripod and wire gauze.
  • Heat the water sample gently.
  • Monitor the temperature of the boiling water using the thermometer.
  • Record the temperature at which the water starts to boil and the temperature at which it is boiling steadily.

• Interpretation: Pure water boils at 100°C at standard atmospheric pressure. Impurities will raise the boiling point. The boiling point will be higher than 100°C, and the boiling point depression will be proportional to the concentration of the impurities. A significant deviation from 100°C indicates the presence of dissolved substances.

Two possible sources of metal compounds in river water are:

• Weathering of rocks and soil: Rocks and soil naturally contain various metals. Weathering processes (e.g., chemical weathering) release these metals into the water.
• Industrial discharge: Industrial processes can release metal ions into water through wastewater discharge.

A method to test for iron(II) ions (Fe²⁺) is as follows:

1. Add a few drops of potassium ferrocyanide solution to a sample of the water.
2. If iron(II) ions are present, a blue precipitate of Prussian blue will form. The intensity of the blue color will indicate the concentration of iron(II) ions.