Chemistry MCQs

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Saturated hydrocarbons will generally give a clean flame while unsaturated carbon compounds will give a yellow flame with lots of black smoke. However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons giving a sooty flame.

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Neo-prene is a synthetic rubber which resembles natural rubber in its properties. It is obtained by polymerization of chloroprene.

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Soaps that float in water are made by beating tiny air bubbles before their hardening. Transparent soaps are made by dissolving the soap in ethanol and then evaporating the excess solvent.

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The electrons in the outermost occupied shell (or shells) determine the chemical properties of the atom; it is called the valence shell. Each shell consists of one or more subshells, and each subshell consists of one or more atomic orbitals.

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24 carat is pure gold with no other metals. Lower caratages contain less gold; 18 carat gold contains 75 per cent gold and 25 per cent other metals, often copper or silver. The minimum caratage for an item to be called gold varies by country.

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Olfactory indicator are those substances whose smell can help to distinguish between acids and bases. Onion Juice loses its characteristic smell in Basic solution and retains its smell in Acidic solution; so it serves as olfactory indicator. Similarly, Vanilla extract also loses its smell in basic solution and retains its smell in Acidic solution. Clove oil is also olfactory indicator but its not for weak acids and basic solutions.

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Limestone, chalk and marble are different forms of calcium carbonate (CaCO₃).

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Atomic theory of matter was proposed by John Dalton. Atomic theory before Dalton existed as philosophical concept which later became a part of science. In Greek atomos means indivisible.

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Ionic compounds are made up of a metal and non-metal, and covalent compounds are made up of two non-metals forming polar or non-polar covalent compounds. In the carbon tetrachloride molecule, four chlorine atoms are positioned symmetrically as corners in a tetrahedral configuration joined to a central carbon atom by single covalent bond.

• CH4 + 4Cl2 —> CCl4 + 4HCl

Notes:
According to the Collision Theory, a chemical reaction can occur only when the reactant molecules, atoms, or ions collide with more than a certain amount of kinetic energy and in the proper orientation. In order to effectively initiate a reaction, the reactants must be moving fast enough (with enough kinetic energy) so that they collide with sufficient force for bonds to break. This is known as the activation energy. However, even if two molecules collide with sufficient activation energy, there is no guarantee that the collision will be successful. In fact, not every collision is successful, even if molecules are moving with enough energy. The reason for this is because molecules also need to collide with the right orientation, so that the proper atoms line up with one another, and bonds can break and re-form in the necessary fashion. An effective collision is defined as one in which molecules collide with sufficient energy and proper orientation, so that a reaction occurs. For example, in the gas-phase reaction of dinitrogen oxide with nitric oxide, the oxygen end of N2O must hit the nitrogen end of NO; if either molecule is not lined up correctly, no reaction will occur upon their collision, regardless of how much energy they have.