Activity 1.2 is a practical experiment from the NCERT Class 10 Science textbook that demonstrates a double displacement reaction. In this activity, you mix lead nitrate solution (&&\ce{Pb(NO3)2}&&) with potassium iodide solution (&&\ce{KI}&&) in a test tube. The result is the immediate formation of a bright yellow precipitate of lead iodide (&&\ce{PbI2}&&), while potassium nitrate (&&\ce{KNO3}&&) remains dissolved in the solution. This activity provides visual evidence of a chemical reaction and helps students understand how ions exchange partners during reactions. ,

The yellow precipitate formed in Activity 1.2 is lead iodide (&&\ce{PbI2}&&). It appears as a bright yellow solid that settles at the bottom of the test tube. Lead iodide is insoluble in water at room temperature, which is why it precipitates out of the solution rather than remaining dissolved. The yellow colour is characteristic of lead iodide and makes this reaction easy to identify. The precipitate forms instantly when the two colourless solutions are mixed, providing dramatic visual evidence of the chemical reaction. ,

Activity 1.2 demonstrates a double displacement reaction (also called a double replacement or metathesis reaction). In this type of reaction, the cations and anions of two different compounds exchange places to form two new compounds. Specifically, lead ions (&&\ce{Pb^{2+}}&&) from lead nitrate combine with iodide ions (&&\ce{I^-}&&) from potassium iodide to form lead iodide, while potassium ions (&&\ce{K^+}&&) combine with nitrate ions (&&\ce{NO3^-}&&) to form potassium nitrate. This is also classified as a precipitation reaction because one of the products (lead iodide) is an insoluble solid that precipitates out of solution.

A precipitate forms in Activity 1.2 because lead iodide (&&\ce{PbI2}&&) is insoluble in water. When lead nitrate and potassium iodide solutions are mixed, all four ions (&&\ce{Pb^{2+}}&&, &&\ce{NO3^-}&&, &&\ce{K^+}&&, and &&\ce{I^-}&&) are present in the solution. The lead ions and iodide ions have a strong attraction to each other and combine to form lead iodide. However, because lead iodide cannot dissolve in water, it immediately separates from the solution as a solid precipitate. Meanwhile, potassium nitrate is highly soluble and remains dissolved in the water. The formation of an insoluble product drives the reaction forward.

Safety is crucial when performing Activity 1.2 because lead compounds are toxic. Here are the essential precautions: (1) Always wear safety goggles and gloves to prevent contact with skin and eyes. (2) Perform the experiment only under teacher supervision. (3) Work in a well-ventilated area. (4) Never touch or taste the chemicals. (5) If any solution spills on your skin, wash immediately with plenty of water and inform your teacher. (6) Dispose of the waste properly according to your school’s laboratory guidelines – do not pour lead compounds down the drain. (7) Wash your hands thoroughly after the experiment. Lead is a heavy metal that can accumulate in the body and cause serious health problems, so proper handling is essential.

Double displacement reactions have numerous practical applications in everyday life and industry: (1) Water Treatment: Precipitation reactions are used to remove harmful ions like lead, mercury, and arsenic from water by converting them into insoluble compounds that can be filtered out. (2) Photography: Silver halide precipitation reactions were historically used in photographic film development. (3) Medicine: Barium sulfate (&&\ce{BaSO4}&&), formed by a double displacement reaction, is used as a contrast agent in X-rays. (4) Qualitative Analysis: Chemists use precipitation reactions to identify unknown ions in solutions. (5) Manufacturing: Production of pigments, dyes, and other chemicals often involves precipitation reactions. (6) Soap Making: The reaction between fats and sodium hydroxide involves double displacement. These applications show how understanding simple lab reactions helps us solve real-world problems!

To write the balanced equation for Activity 1.2, follow these steps: Step 1: Write the formulas of reactants and products: &&\ce{Pb(NO3)2 + KI -> PbI2 + KNO3}&&. Step 2: Count atoms on each side. Lead nitrate has 2 nitrate groups, so we need 2 potassium nitrate molecules on the product side. Step 3: To get 2 potassium atoms, we need 2 molecules of potassium iodide on the reactant side. Step 4: Check: This also gives us 2 iodide atoms, which is correct for lead iodide (&&\ce{PbI2}&&). Final balanced equation: &&\ce{Pb(NO3)2(aq) + 2KI(aq) -> PbI2(s) + 2KNO3(aq)}&&. The coefficient 2 before KI and KNO3 ensures that we have the same number of each type of atom on both sides, following the Law of Conservation of Mass. Don’t forget to include state symbols: (aq) for aqueous and (s) for solid!

Though they may look similar, precipitates and sediments are formed by different processes: A precipitate is a solid that forms as a result of a chemical reaction in a solution. For example, the yellow lead iodide in Activity 1.2 is a precipitate because it forms when two dissolved compounds react chemically. The formation of a precipitate involves breaking old chemical bonds and forming new ones, creating a new substance with different properties. On the other hand, a sediment is solid particles that settle out of a suspension due to gravity, without any chemical reaction occurring. For example, if you mix sand with water and let it stand, the sand will settle at the bottom as sediment – but it’s still sand, not a new substance. The key difference is: precipitates result from chemical changes, while sediments result from physical settling.