Chemistry Facts for Competitive exams
CHEMICAL REACTIONS AND EQUATIONS
1) A chemical equation consists of two entities
a) Reactants – These are written on the left hand side of the equation
b) Products – These are written on the right side of the equation
2) A chemical equation must be always balanced. i.e number of atoms on reactant side should be same as that on product side.
3) Chemical reactions are classified as follows:
a) Combination reaction – two reactants combine to form a single product.
b) Decomposition reaction – a single reactant decomposes to give out two or more products.
c) Displacement reaction – occurs when an element replaces another element from its compound.
d) Double displacement reaction – occurs when atoms or group of atoms are exchanged.
4) The properties of the product will be entirely different from that of the reactant or reactants.
5) Reactions during which energy is absorbed is called endothermic reaction.
6) Reactions during which energy is released is called exothermic reaction.
7) Oxidation is the gain of oxygen or loss of hydrogen.
8) Reduction is the loss of oxygen or gain of hydrogen.
9) Decomposition reaction is used in black and white photography.
10) Rusting of iron is an example of chemical reaction of iron with atmosphere.
ACIDS, BASES AND SALTS
1) Acid are – sour to taste……change the color of blue litmus paper to red
2) Bases are – bitter to taste…..changes the color of red litmus to blue.
3) Acid-base indicators are dyes or mixture of dyes to identify an acid or a base.
a) Litmus paper is an indicator. It is neither acidic nor basic.
b) Some examples of natural indicators are – cabbage leaves, turmeric colored petals of flowers like Petunia, Geranium etc.
4) Acidic character of a substance is due to formation of H+ ions in their solution.
5) Basic character of a substance is due to formation of OH- ions in it’s solution.
6) Hydrogen gas and salt of formed when a base reacts with metal.
7) When acid reacts with a metal carbonate or a metal hydrogen-carbonate, a corresponding salt, carbon dioxide and water is formed.
8) Acidic and basic solutions in water conduct electricity because they produce hydrogen and hydroxide ions respectively.
9) Strength of an acid or base can be measured using a pH scale.
i) the scale has values ranging from 0-14
ii) An acid solution has a pH less than 7 whereas a basic solution has a pH more than 7.
iii) A neutral solution has a pH of exactly 7.
10) An acid and base react with each other to form a neutral product i.e a corresponding salt and water.
a) This reaction is called neutralization reaction.
METALS AND NON-METALS
1) Every elements in this universe is classified into metals and non-metals.
2) Metals are
d) Good conductors of heat and electricity.
e) Solid at room temperature except mercury.
3) Non-metals are:
a) Not malleable
b) Not ductile
c) Poor conductors of heat and electricity. Graphite is an exception.
4) Metals can form positive ions by losing electrons to non-metals.
5) Metals combine with oxygen to form basic oxides.
6) Non-metals form negatively charged ions by gaining electrons when reacting with metals.
7) Non-metal oxides are either acidic or neutral.
8) Non-metals do not displace hydrogen from dilute acids but they react with hydrogen to form hydrides.
9) A reactivity series is a list of metals that order are arranged in the order of their decreasing reactivity.
a) Metals above hydrogen in this series can replace hydrogen from dilute acids.
10) A more reactive metal can displace a less reactive metal from its salt solution.
11) Less reactive metal like gold exists in nature as free element.
12) Metallurgy is termed as the extraction of metals from it’s ores and refining it for commercial use.
CARBON AND IT’S COMPOUNDS
1) Carbon is the basis of all living organisms as well as most of the things we use in our daily life.
2) Carbon forms a large variety of compounds because of its tetra-valency and the property called catenation.
3) Covalent bonds are formed by sharing of electrons between two atoms so that both of then can achieve a completely filled outermost shell.
4) Carbon forms covalent bonds with itself and other elements such add hydrogen, oxygen, sulphur and chlorine.
5) Carbon forms compounds containing double and triple bonds between carbon atoms.
i) These carbon chains may be straight, branched chains or rings.
ii) Carbon and it’s compounds are some of the major sources of fuel.
6) Some of the allotropes of carbon are
i) The chemical property of allotropes are same but they have entirely different physical properties.
CLASSIFICATION OF ELEMENTS
1) Elements are classified according to their similarities in their properties.
2) Mendeleev arranged the elements according to they increasing order of their atomic masses and also according to their chemical properties.
3) Mendeleev correctly predicted the existence of undiscovered elements from the gaps he observed in gist periodic table.
4) Modern periodic table is the modified version of Mendeleev’s periodic table.
5) Elements in modern periodic table are arranged in 18 columns called groups and 7 rows called periods.