Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Matter is classified into pure substances and mixtures. Pure substances include elements consisting of only one type of atom, such as or , and compounds which are chemically combined elements in fixed proportions, such as .
A mixture consists of two or more substances physically combined. Components retain their individual properties and can be separated by physical methods. Mixtures can be homogeneous (uniform composition) or heterogeneous (non-uniform).
Synthetic fibres are polymers made of small repeating units called monomers. This process of joining monomers is called polymerization.
Rayon is known as 'artificial silk' because it is derived from natural cellulose but processed chemically. Nylon was the first fully synthetic fibre made from coal, water, and air.
Polyester is a polymer of repeating units of an organic chemical called an ester. A common form used for bottles and utensils is (Polyethylene terephthalate).
Plastics are polymers that can be molded. They are categorized into Thermoplastics, which soften on heating (e.g., and Polythene), and Thermosetting plastics, which do not soften once molded due to cross-linking (e.g., Bakelite and Melamine).
The 5R principle for environmental conservation regarding plastics is: Reduce, Reuse, Recycle, Recover, and Refuse.
📐Formulae
💡Examples
Problem 1:
Calculate the mass ratio of elements in a molecule of Ammonia (). (Atomic mass of , )
Solution:
Explanation:
In , there is one Nitrogen atom and three Hydrogen atoms. By multiplying their atomic masses, we get the constant proportion by mass.
Problem 2:
Identify the monomer of Polythene and represent its polymerization.
Solution:
Monomer: Ethene (). Reaction:
Explanation:
Polythene is an addition polymer formed by the linkage of thousands of ethene molecules.
Problem 3:
Why is Bakelite used for making electrical switches instead of PVC?
Solution:
Bakelite is a thermosetting plastic with a cross-linked structure:
Explanation:
Unlike (a thermoplastic), Bakelite does not melt or soften upon heating and is a poor conductor of electricity, making it safer for electrical components.