NCERT Class 10 - Chemistry

• A chemical reaction is a process in which the original substance(s) loses its nature and identity and forms new substance(s) with different properties.
• Breaking of the chemical bonds and formation of new chemical bonds is responsible for the occurrence of a chemical reaction.
• The substances which take part in a chemical reaction are called Reactants.
• The substances which are formed in a chemical reaction are called Products.
• A chemical reaction can be identified by either of the following observations: Change in state, Change in colour, Evolution of gas, Change in temperature, Formation of a precipitate.
• Water of crystallization is the fixed number of water molecules present in one formula unit of a salt.
• Copper sulphate pentahydrate (CuSO4.5H2O) has five water molecules in one formula unit of copper sulphate (blue vitriol).
• Sodium carbonate (Na2CO3.10H2O) has ten molecules of water as water of crystallization.
• Gypsum (CaSO4.2H2O) has two molecules of water as water of crystallization.
• A chemical equation is the symbolic representation of a chemical reaction in the form of symbols and formulae.
• A chemical equation is a way to represent the chemical reaction in a concise and informative way.
• For example, Magnesium + Oxygen → Magnesium oxide is a chemical equation.
• The word equation can be written into chemical equation by writing symbols and formulae of the substance in place of their name.
• In a chemical equation, the symbols of elements and the formulae of reacting substances (reactants) are written on the left hand side of the equation, with a plus (+) sign between them.
• Copper reacts with moist carbon dioxide in air and forms a green coat of copper carbonate.
• Iron acquires a coating of brown flaky substance called rust.
• Rust is hydrated Iron (III) oxide, i.e., Fe2O3.xH2O.
• Corrosion can be prevented by painting, oiling, greasing, galvanizing and by making alloys.
• Galvanization is the process which involves coating of iron with zinc.
• The oxide thus formed in galvanization is impervious to air and moisture, thus protects further layers from getting corroded.
• Alloys are homogeneous mixture of metals with metals and non-metals.
• Stainless steel is an alloy of iron, nickel, chromium.
• Brass is an alloy of copper and zinc.
• Bronze is an alloy of copper and tin.
• Solder is an alloy of lead and tin.
• Amalgam is an alloy if one of the metals is mercury, for example, sodium amalgam and silver amalgam.
• The process of equalizing the atoms of various elements both on either sides of an equation is called the balancing of chemical equation.
• 2AgCl( s ) is heated in sunlight, it decomposes into 2Ag( s ) and Cl 2 ( g ).
• Displacement reactions are the chemical reactions in which more reactive element displaces less reactive element from its salt solution.
• Double displacement reactions are reactions in which new compounds are formed by mutual exchange of ions between two compounds.
• Rusting is a type of corrosion in which iron objects, when left in moist open air, get coated with a reddish brown powder known as rust.
• Corrosion is a wasteful process because it leads to wastage of tonnes of various metals every year and lot of money is spent to repair or replace it.
• Prevention of rusting can be done by painting iron articles, oiling and greasing machine parts, using galvanised iron pipes for water supply, and coating iron with chromium to prevent rusting.
• Heteroatoms: An atom other than carbon or hydrogen atom.
• Alkaline KMnO or Acidic K Cr O 4 2 → CH 3 COOH Ethanol Ethanoic acid.
• Unsaturated hydrocarbons (alkene, alkyne) undergo addition reactions.
• In unsaturated hydrocarbon, hydrogen is added in the presence of catalyst palladium or nickel.
• Vegetable oils are converted into vegetable ghee using this process.
• The process of converting vegetable oils into vegetable ghee is called hydrogenation of vegetable oils.
• Saturated hydrocarbons undergo substitution reaction in the presence of sunlight.