Best ever seen chemistry notes

1. CHEMICAL REACTIONS AND EQUATIONS •••••••
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1. ( 1' 11 I a , cactions ch ' . I .. • •
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or new substanc"..s. are formed' c mrca compos1llon of •• •
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c1,,, ,irt1l Eq11nt1or1. Chem ical reactions b ·. .
2· ronn11 which sh? uld always be balanced. can e w ritten in chemical equation • •
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Tl/pi·~ of Cltet111cnI Reactious: •
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· · ·(i) Combination reaction. A single rod .
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rl'clCtants. p uct is form ed from two or more ■
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~g + 02 - - 2M
(ii) Decomposition reaction. A single reactant f ak d .
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more products. re s own to yield two or ■ ■
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• Thermal decomposition: 2Pb(NO)
• Electrolysis: 2H 3 2 2Pb0 + 4N02 + 02 ■ $l) ■
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• Photochenu cal reaction:
20 _ __,, 2H + 0
2AgBr _ __,, 2A 2 2
(iii) Displacement reaction. One element is di'spl d b g + th Br21
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z C ace Y ano er e ement.
n + uS04 _ __,, ZnS04 + Cu
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(1t1) Double displacement reaction. Exch ange of ions between reactants. ■ ■
AgN03 + NaCl - - AgCl + NaNO ■
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(v) Redox reaction. Both oxidation and reductio~ take place
simultaneously.
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CuO + H 2 - - Cu + H 20
(v,) Exothermic reaction. A chemical reaction in which heat energy is
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C+02 CO2 (g) + heat ■
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(vii) Endothermic reaction. A chemical reaction in which heat energy is
absorbed.
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ZnC03 + Heat - - ZnO + CO2
(viii) Redox reaction. Chemical reaction m which both oxidation and
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reduction take p lace sim ultaneously. •• ..J ••
4. Oxidation. Reaction that involves the gain of oxygen or loss of hydrogen.
5. Reductio11. Reaction that shows the loss of oxygen or gain of hydrogen. ••• ~ ••
ZnO + C - - Zn + CO ·• -C •••
ZnO is reduced to Zn- reduction. C is oxidized to CO-oxidation. • I •
6. Effects of Oxidation Reactions in Our Daily Life:
(1) Corrosion. It is an undesirable change that occurs in metals, when they
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are attacked by moisture, air, acids and bases. . . •
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Example, Corrosion (rusting) of Iron: Fe20 3 . nH20_(Hy_dra ted ~~n oxide) • •
(i1) Rancidity. Undesirable change that takes place m 011 contammg food
items d ue to the oxidation of fatty acids.
Preventive methods of rancidity. Adding antioxidants to the food
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materials, storing food in air tight container, flushing out air with •
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nitrogen gas and refrigeration. •
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, 2. ACIDS, BASES AND SALTS
h'ch turn blue litmus solution red are called acids. Acids are
1. Acids. Substances w 1 5 our in
taste. all d b
2 • .Bases. Su bs tan Ce
s which change red litmus solution blue are c e ases. They are bitter 111
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taste.
3. Mineral Acids. Acids which are obtained from miner'.31s ~ e sulphates, ~tr~tes, ~Orides etc.
are called mineral acids, example, H 2S04 (Sulphunc aod), HNO3 (N1tr1c acid) and 1-iCI
(Hydrochloric acid).
4. Organic Acids. Acids which are obtained fr~m pl~ts ~d ~als _are called organic acids.
Example citric acid, ascorbic acid, tartaric acid, lactic acid, acetic acid.
5. Hydroni'um Ions. They are formed by reaction of H + (from acid) and HzO- It is because H+is
unstable.
6. Universal Indicator. A universal indicator is a mixture o f indica tors which shows a gradual
but well-marked series of colour changes over a very wide range of change in concentration
of H + ions.
7. Strong Acids. Acids which dissociate into ions complet-ely are called strong acids. Example,
H2 S04, HCI.
8. Weak Acids. Acids which do not dissociate into ions completely are called weak acids.
Example, citric acid, acetic acid.
9. Chemical Properties of Acids:
(1) Acids react with active m etals to give salt and hydrogen gas.
(it) Acids react with metal carbonates and metal hydrogen carbonates to give salt, water
and carbon dioxide.
(iiz) Acids react with bases to give salt and water. This reaction is called neutralization
reaction.
(iv) Acids react with metal oxides to give salt and water.
10. Chemical Properties of Bases:
(1) Reaction with metaJ~. ('prtain metals such as zinc, aluminium and tin react with alkali
solutions on heating .ind h_vdrogen gas is evolved.
(i1) Reaction with acids. Bc1~,, react with acids to form salt and water.
11. Indicators. Indicators are SUl>:-t.tnces which indicate the acidic or basic nature of the solution
by their colour change.
12. pH Scale. A scale for measurin.g hydrogen ion concentration in a solution.
The pH of a solution is defined as the negative logarithm of hydrogen ion concentration in
moles per litre.
pH = -log [H+]
pH = -log [H3O+j
where [H+J or [H3O +] represents concen trations of hydrogen ions in a solution.
The pH of a neutral solution is 7.
The pH of an acidic solution is < 7.
The p H of a basic solutio1, i" > 7.