Chemistry Keypoints: Water; Water is a common and essential substance that is vital for life on Earth. This article will cover various topics related to water, including its composition, properties as a solvent, and various types of water.
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(a) Water is a product of the combustion of hydrogen and its composition by volume.
Water is a compound made up of two hydrogen atoms and one oxygen atom. Its chemical formula is H2O. Water is formed by the combustion of hydrogen gas with oxygen gas. The composition of water by volume is two parts hydrogen to one part oxygen.
(b) Water as a solvent, atmospheric gases dissolved in water, and their biological significance.
Water is a versatile solvent because of its polarity and ability to dissolve many substances, including polar and ionic compounds. The atmospheric gases such as nitrogen, oxygen, and carbon dioxide dissolve in water and are crucial for supporting aquatic life.
Dissolved oxygen is necessary for fish and other aquatic organisms to breathe, while dissolved carbon dioxide is needed by aquatic plants for photosynthesis. Nitrogen is also essential for aquatic plant growth.
(c) Hard and soft water: Temporary and permanent hardness and methods of softening hard water.
Hard water is water that contains high levels of dissolved minerals, primarily calcium and magnesium ions. The hardness of water is measured in parts per million (ppm) or grains per gallon (gpg).
Temporary hardness is caused by the presence of bicarbonate ions, which can be removed by boiling the water or adding lime. Permanent hardness is caused by the presence of calcium sulfate or magnesium sulfate, which cannot be removed by boiling the water.
Several methods can be used to soften hard water, including ion exchange, reverse osmosis, and distillation. In ion exchange, the hard water is passed through a resin that removes the calcium and magnesium ions and replaces them with sodium ions.
In reverse osmosis, the water is forced through a membrane that removes the dissolved minerals. Distillation involves boiling the water and then condensing the steam to remove the minerals.
(d) Treatment of water for town supply.
Water treatment is essential for providing safe and clean drinking water for communities. The process typically involves several steps, including coagulation, sedimentation, filtration, disinfection, and distribution. Coagulation involves adding chemicals such as alum to the water to create flocs that attract and remove impurities.
The water is then allowed to settle in a sedimentation tank, where the flocs sink to the bottom. The clear water is then passed through filters to remove any remaining impurities. Finally, the water is disinfected with chlorine or other chemicals to kill any remaining bacteria and viruses before being distributed to consumers.
(e) Water of crystallization, efflorescence, deliquescence, and hygroscopy. Examples of the substances exhibiting these properties and their uses.
The water of crystallization is water that is bound into the crystal lattice of some substances. Efflorescence occurs when these crystals lose their water of crystallization when exposed to air. Deliquescence is the opposite of efflorescence, where a substance absorbs water from the air and becomes moist.
Hygroscopy is the ability of a substance to absorb moisture from the air without deliquescing. Examples of substances that exhibit these properties include copper sulfate, which forms blue crystals with five water molecules bound in its lattice, and sodium chloride, which can absorb moisture from the air and become damp.
In conclusion, water is a fascinating and essential substance that plays a crucial role in our lives. Its composition, properties, and behavior as a solvent, as well as its different types, are all important to understand.
Formulas: Water
- The formula for water: H2O
- Molarity (M) = moles of solute/liters of solution
- Molality (m) = moles of solute/kilograms of solvent
- Parts per million (ppm) = (mass of solute / total mass of solution) x 10^6
- Henry’s law constant: C = kH x P, where C is the concentration of gas in solution, kH is Henry’s law constant for a particular gas, and P is the partial pressure of the gas above the solution.
- The equilibrium constant (Kc) = [products] / [reactants], where [products] and [reactants] are the concentrations of the respective species at equilibrium.
- The acid dissociation constant (Ka) and base dissociation constant (Kb), describe the strength of acids and bases, respectively.
- pH = -log[H+], where [H+] is the concentration of hydrogen ions in solution.
- pOH = -log[OH-], where [OH-] is the concentration of hydroxide ions in the solution.
- Kw = [H+][OH-], where Kw is the ion product constant for water, which is equal to 1.0 x 10^-14 at 25°C.
