Saturday, 27 October 2018
MCQs 1 on STRUCTURE OF THE ATOM => 9th Class
MCQs 1 on Is MATTER AROUND US PURE ? => 9th Class
Friday, 26 October 2018
MCQs 2 on MATTER IN OUR SURROUNDINGS) => 9th Class
MCQs 1 on MATTER IN OUR SURROUNDINGS) => 9th Class
Friday, 10 November 2017
Online 10th CLASS NCERT CHEMISTRY (Practice CHEMISTRY Test for Chapters => 1, 2, 3, 4)
Online 10th CLASS NCERT Practice CHEMISTRY Tests for Chapters => 1, 2, 3, 4
Chemistry Test
Time:1 hour 30 min Marks:
35
Q.1 A solution of a substance ‘X’ is used for white
washing. 3
(i)
Name the substance ‘X’ and write its formula.
(ii)
Write the reaction of the substance ‘X’ named in (i) above with
water.
Q.2 Write the balanced chemical
equations for the following reactions. 2
(a) Calcium hydroxide +
Carbon dioxide => Calcium carbonate + Water
(b) Zinc + Silver nitrate => Zinc nitrate + Silver
Q.3 A shiny brown coloured element ‘X’ on heating in air becomes
black in colour. 1
Name the element ‘X’ and
the black coloured compound formed.
Q.4 Which
gas is usually liberated when an acid reacts with a metal? Illustrate with an
example. How will you test for the presence of this gas? 3
Q.5 How
is the concentration of hydronium ions (H3O+) affected when a solution of an acid is diluted?2
Q.6 Plaster of Paris should be
stored in a moisture-proof container. Explain why? 2
Q.7 Give two important uses of
washing soda and baking soda. 2
Q.8 Which gas is produced when dilute hydrochloric acid is added
to a reactive metal? Write the chemical reaction when iron reacts with dilute H2SO4. 2
Q.9 Name two metals which are found in nature in the free state. 2
Q.10 What are amphoteric oxides? Give two examples of
amphoteric oxides. 2
Q.11 You
must have seen tarnished copper vessels being cleaned with lemon or tamarind juice.
Explain why these sour substances are effective in cleaning the vessels. 2
Q.12 Differentiate between metal and non-metal on the basis of
their chemical properties. 2
Q.13 Draw the structures for the following compounds. 5
(i)
Ethanoic acid (ii)
Bromopentane* (iii) Butanone (iv) Hexanal.
*Are structural isomers possible for
bromopentane?
Q.14 A mixture of oxygen and
ethyne is burnt for welding. Can you tell why a mixture of ethyne and air is
not used? 2
Q.15 How can ethanol and ethanoic acid be differentiated on the
basis of their physical
and
chemical properties? 3
Saturday, 7 October 2017
Online Notes on Chapter=2 ( Acids, Bases and Salts) Part 2
This is Online Notes on Chapter=2 ( Acids, Bases and Salts) Part 2 for preparation of CBSE BOARD Examination, NTSE etc.Acid or Base in Water Solution
• Acids produce H+ ions in presence of water.
• H+ ions cannot exist alone, they exist as H2O+ (hydronium ions).
H+ + H2O → H3O+
HCl + H2O → H3O+ + Cl−
Bases when dissolved in water gives OH- ions.
NaOH ==H2O=> Na+ + OH-
Mg(OH)2 ==H2O==> Mg2+ + 2OH-
• Bases soluble in water are called alkali.
• While diluting acids, it is recommended that the acid should be added to water
and not water to acid because the process of dissolving an acid or a base in
water is highly exothermic.
Strength of Acid and Base
Strength of acid or base can be estimated using universal indicator.
Universal indicator : is a mixture of several indicators. It shows different colours at different concentrations of H+ ions in the solution.
pH Scale : A scale for measuring H+ ion concentration in a solution . p in pH stands for ‘potenz’ a German word which means power.
pH = 7 → neutral solution
pH less than 7 → acidic solution
pH more than 7 → basic solution
pH of Salts :
(i) Strong Acid + Strong Base → Neutral Salt : pH = 7
(ii) Salt of strong acid + Weak base → Acidic salt : pH < 7
(iii)Salt of strong base + Weak acid → Basic salt : pH > 7
1. Sodium Hydroxide (NaOH) : When electricity is passed through an aqueous
solution of NaCl (brine), it decompose to form NaOH. (Chlor-alkali process)
2NaCl + 2H2O → 2NaOH + Cl2 + H2
At anode : Cl2 gas
At cathode : H2 gas
Near cathode : NaOH solution is formed.
Uses :
H2 : Fuels, margarine
Cl2 : Water treatment, PVC, CFC’s
HCl : Cleaning steels, medicines
NaOH : Degreasing metals, soaps and paper making
Cl2 + NaOH → Bleach : Household bleaches, bleaching fabrics
2. Bleaching Powder (CaOCl2) : It is produced by the action of chlorine on dry
slaked lime.
Cl2 + Ca(OH)2 → CaOCl2 + H2O
Uses :
(a) Bleaching cotton and linen in textile industry.
(b) Bleaching wood pulp in paper factories.
(c) Oxidizing agent in chemical industries.
(d) Disinfecting drinking water.
3. Baking Soda (Sodium Hydrogen Carbonate) (NaHCO3) :
NaCl + H2O + CO2 + NH3→ NH4Cl + NaHCO3
Baking soda
• It is mild non-corrosive base.
• When it is heated during cooking :
2NaHCO3 ==Heat=> Na2CO3 + H2O + CO2
Uses :
(a) For making baking powder (mixture of baking soda and tartaric acid). When
baking powder is heated or mixed with water, CO2 is produced which causes
bread and cake to rise making them soft and spongy.
(b) An ingredient in antacid.
(c) Used in soda acids, fire extinguishers.
4. Washing Soda (Na2CO3.10H2O) : Recrystallization of sodium carbonate gives
washing soda. It is a basic salt.
Na2CO3 + 10H2O → Na2CO3.10H2O
Uses :
(a) In glass, soap and paper industry.
(b) Manufacture of borax.
(c) Cleaning agent for domestic purposes.
(d) For removing permanent hardness of water.
5. Plaster of Paris (Calcium sulphate hemihydrates) (CaSO4.½H2O) : On heating gypsum (CaSO4.2H2O) at 373K, it loses water molecules and becomes Plaster of Paris (POP).
It is a white powder and on mixing with water it changes to gypsum.
CaSO4.½H2O + 1½H2O → CaSO4.2H2O
Uses :
(a) Doctors use POP for supporting fractured bones.
(b) For making toys, material for decoration.
(c) For making surfaces smooth.
Water of Crystallization : It is a fixed number of water molecules present in one formula unit of a salt.
E.g., CuSO4.5H2O has 5 water molecules.
Na2CO3.10H2O has 10 water molecules.
CaSO4.2H2O has 2 water molecules.
Online Notes on Chapter=2 ( Acids, Bases and Salts) Part 1
This is Online Notes on Chapter=2 ( Acids, Bases and Salts) Part 1 for preparation of CBSE BOARD Examination, NTSE etc.ACIDS :
• These are the substances which have sour taste.
• They turn blue litmus solution red.
• They give H+ ions in aqueous solution.
• The term ‘acid’ has been derived from the Latin word, acidus, which means
sour.
Strong Acids : HCl, H2SO4
Weak Acids : CH3COOH, Oxalic acid, Lactic acid
Concentrated Acid : Having more amount of acid + less amount of water
Dilute Acid : Having more amount of water + less amount of acid
BASES :
• These are the substances which are bitter in taste and soapy in touch.
• They turn red litmus solution blue.
• They give OH- ions in aqueous solution.
Strong Bases : NaOH, KOH, Ca(OH)2
Weak Bases : NH4OH
Alkalis : These are bases which are soluble in water [NaOH, KOH, Ca(OH)2].
SALTS :
These are the compounds formed from reaction of acid and base.
Example : NaCl, KCl.
INDICATORS :
These are the substances which change their colour/smell in different types of
substances.
Reaction of Metallic Oxides with Acids
Metallic oxides are basic in nature.
E.g., CaO, MgO are basic oxides.
Metallic Oxide + Acid → Salt + H2O
CaO + 2HCl → CaCl2 + H2O
Reaction of Non-metallic Oxides with Bases
Non-metallic oxides are acidic in nature.
Non-metallic Oxide + Base → Salt + H2O
CO2 + Ca(OH)2 → CaCO3 + H2O
Thursday, 5 October 2017
Online Notes on Chapter=1 ( Chemical Reactions and Equations) Part 2
This is Online Notes on Chapter=1 ( Chemical Reactions and Equations)) Part 2 for preparation of CBSE BOARD Examination, NTSE etc.=> TYPES OF CHEMICAL REACTIONS:
I. COMBINATION REACTION : The reaction in which two or more reactant combine to form a single product.
e.g. (i) Burning of coal
C (s) + O2 (g) → CO2 (g)
(ii) Formation of water
2H2 (g) + O2 (g) → 2H2O (l)
(iii) CaO (s) + H2O (l) → Ca(OH)2 (aq)
Quick lime Slaked lime
=> Exothermic Reactions : Reaction in which heat is released along with formation of products.
e.g., (i) Burning of natural gas
CH4 (g) + O2 (g) → CO2 (g) + 2H2O (g) + Heat
(ii) Respiration is also an exothermic reaction.
C6H12O6 (aq) + 6O2 (g) → 6CO2 (aq) + 6H2O (l) + energy
II. DECOMPOSITION REACTION : The reaction in which a compound splits into two or more simple substances is called decomposition reaction.
A → B + C
• Thermal decomposition : When decomposition is carried out by
heating.
e.g., (i) 2FeSO4 (s) ==HEAT==> Fe2O3 (s) + SO2 (g) + SO3 (g)
(Ferrous sulphate) (Ferric oxide)
Green colour Red-brown colour
(ii) CaCO3 (s) ==Heat==> CaO (s) + CO2 (g)
(Lime stone) (Quick lime)
• Electrolytic Decomposition : When decomposition is carried out by
passing electricity.
e.g., 2H2O ==Electric current==> 2H2 + O2
e.g., 2AgCl (s) ==Sunlight==> 2Ag (s) + Cl2 (g)
2AgBr (s) ==Sunlight==> 2Ag (s) + Br2 (g)
* Above reaction is used in black & white photography.
• Endothermic Reactions : The reactions which require energy in the
form of heat, light or electricity to break reactants are called endothermic
reactions.
III. DISPLACEMENT REACTION : The chemical reaction in which more reactive element displaces less reactive element from its salt solution.
Fe (s) + CuSO4 (aq) → FeSO4 (aq) + Cu (s)
The iron nail becomes brownish in colour by deposition of Cu and blue colour of
CuSO4 changes dirty green colour due to formation of FeSO4.
Zn + CuSO4 → ZnSO4 + Cu
Zn is more reactive than copper.
IV. DOUBLE DISPLACEMENT REACTION : A reaction in which new compounds are formed by mutual exchange of ions between two compounds.
Na2SO4 (aq) + BaCl2 (aq) → BaSO4 (s) + 2NaCl (aq)
(Sodium (Barium (Barium (Sodium
sulphate) chloride) sulphate) chloride)
White precipitate of BaSO4 is formed, so it is also called precipitation reaction.
V. OXIDATION AND REDUCTION :
Oxidation :
i) The addition of oxygen to substance.
(ii) The removal of hydrogen from a substance.
C + O2 → CO2
2Cu + O2 ==Heat==> 2CuO
CuO + H2 ==Heat==> Cu + H2O
Reduction :
(i) The addition of hydrogen to substance.
(ii) The removal of oxygen from a substance.
In this reaction CuO is reduced to Cu and H2 is oxidized to H2O. So, oxidation and reduction taking place together is redox reaction.
=> Effects of Oxidation in Daily Life:
1) Corrosion :
• When a metal is exposed to substances such as moisture, acid etc. for some
time, a layer of hydrated oxide is formed which weakens the metal and hence
metal is said to be corrode
• Rusting of iron, black coating on silver and green coating on copper are
examples of corrosion.
• Corrosion can be prevented by galvanization, electroplating or painting.
2) Rancidity : The oxidation of fats and oils when exposed to air is known as
rancidity. It leads to bad smell and bad taste of food.
=> Methods to Prevent Rancidity :
(i) By adding antioxidants
(ii) Keeping food in air tight containers
(iii) Replacing air by nitrogen
(iv) Refrigeration.
Online Notes on Chapter=1 ( Chemical Reactions and Equations) Part 1
This is Online Notes on Chapter=1 ( Chemical Reactions and Equations)) Part 1 for preparation of CBSE BOARD Examination, NTSE etc.=> The process in which new substances with new properties are formed from
one or more substances is called Chemical Reaction.
* The substances which take part in chemical reaction are called Reactants.
* The substances which are formed in a chemical reaction are called Products.
Examples :
(i) Digestion of food
(ii) Respiration
(iii) Rusting of iron
(iv) Burning of Magnesium ribbon
(v) Formation of curd
=> Chemical reaction involves :
• Change in state
• Change in colour
• Change in temperature
• Evolution of gas
=> Chemical Equation:
* A chemical reaction can be represented by chemical equation. It involves uses
of symbol of elements or chemical formula of reactant and product with
mention of physical state.
* The necessary conditions such as temperature, pressure or any catalyst should
be written on arrow between reactant and products.
e.g., Magnesium is burnt in air to form magnesium oxide.
Mg + O2 → MgO
=> Balancing Chemical Equation:
* Law of conservation of Mass. Matter can neither be created nor destroyed in a
chemical reaction.
* So number of elements involved in chemical reaction should remain same at
reactant and product side.
=> STEPWISE BALANCING (Hit and Trial):
Step 1. Write a chemical equation and draw boxes around each formula.
Fe + H2O → Fe3O4 + H2
* Do not change anything inside the box.
Step 2. Count the number of atoms of each element on both the sides of chemical
equation.
Step 3. Equalise the number of atoms of element which has maximum number by putting in front of it.
Fe + 4H2O → Fe3O4 + H2
Step 4. Try to equalize all the atoms of elements on reactant and product side by
adding coefficient in front of it.
3Fe + 4H2O → Fe3O4 + 4H2
* Now all the atoms of elements are equal on both sides.
Step 5. Write the physical states of reactants and products.
3Fe (s) + 4H2O (g) → Fe3O4 ( s) + 4H2 (g)
Solid state = (s)
Liquid state = (l)
Gaseous state = (g)
Aqueous state = (aq)
Step 6. Write necessary conditions of temperature, pressure or catalyst on arrow
above or below.
Online Notes on Chapter=5 ( Periodic Classificatoin of Elements) Part 2
This is Online Notes on Chapter=5 ( Periodic Classificatoin of Elements) Part 2 for preparation of CBSE BOARD Examination, NTSE etc.=> Modern Periodic Table:
• Atomic number of an element is a more fundamental property than its
atomic mass.
• According to the Modern Periodic law : The properties of elements are a
periodic function of their atomic number.
• All the anomalies of Mendeleev’s classification disappear.
=> Merits of Mendeleev’s Periodic Table:
(i) Some gaps were left for the undiscovered elements like gallium (Ga),
Scandium (Sc) and Germanium (Ge).
(ii) Predict properties of elements on the basis of their positions in the
periodic table.
(iii) Accommodate noble gases when they were discovered without
disturbing the original arrangement.
=> Limitations of Mendeleev’s Classification:
(i) Position of isotopes could not be explained.
(ii) No fixed position for hydrogen.
(iii) Wrong order of atomic masses of some elements could not be explained.
Explanation of the Anomalies :
(i) Explanation for the position of isotopes (Same atomic number put at one
place in the same group).
(ii) Cobalt with atomic number 27 came first and nickel (28) should come
later.
(iii) Unlike atomic masses, atomic number is always a whole number, so
there is no element between hydrogen and helium.
• Atomic Number : It is denoted by Z and equal to the number of protons
in the nucleus of an atom.
• Modern Periodic table has 18 vertical columns known as ‘groups’ and 7
horizontal rows known as ‘periods’.
• Elements with same number of valence electrons are placed in the same
group. For example,
Li : 2, 1 Na : 2, 8, 1 K : 2, 8, 8, 1
Outermost or valence shell in all the three contains 1 electron. These elements
have been placed in the same group.
• Number of shells increases as we go down the group.
• Elements with same number of occupied shells are placed in same period.
For example, Li (2, 1); Be (2, 2); B (2, 3), C (2, 4), N(2, 5). These
elements have same number of shells (two).
• Each period marks a new electronic shell getting filled.
• Number of elements placed in a particular period depends upon the fact
that how electrons are filled into various shell.
• Maximum number of electrons that can be filled in a shell is given by 2n2
where n is shell number.
E.g., K shell n = 1 or 2n2 = 2(1)2 = 2 First period has 2 elements.
L shell n = 2 or 2n2 = 2(2)2 = 8 Second period has 8 elements.
• Position of an element in the periodic table tells us its chemical reactivity.
• Valence electron determine the kind and number of bonds formed by the
element.
=> Trends in the Modern Periodic Table:
Valency : No. of valence electrons present in the outermost shell of its atom.
On moving from left to right in each period, the valency of elements increases
from 1 to 4 and then decreases to 0.
Metallic Character:
• Metallic character means the tendency of an atom to lose electron.
• Metals occupy the left hand side of the periodic table.
• On moving left to right in a period, the metallic character of an element
decreases because the effective nuclear charge increases. It means
tendency to lose electron decreases.
• Metals are electropositive as they tend to lose electrons while forming
bonds.
• Metallic character increases as we go down a group as the effective
nuclear charge is decreasing.
Non-metallic Character
• Non-metals are electronegative as they tend to form bonds by gaining
electrons.
• Non-metals occupies the right side of the periodic table.
• Non-metallic character increases across a period because due to increase
in effective nuclear charge that means tendency to gain electron increase.
• Non-metallic character decreases as we move down a group due to
decrease in effective nuclear charge experienced by the valence electron
thus the tendency to gain electron decreases.
• In the middle of periodic table we have semi-metals or metalloid because
they exhibit some properties of metals and non-metals.
• Oxides of metals are basic in nature while oxides of non-metals are acidic
in nature.
Online Notes on Chapter=5 ( Periodic Classificatoin of Elements) Part 1
This is Online Notes on Chapter=5 ( Periodic Classificatoin of Elements) Part 1 for preparation of CBSE BOARD Examination, NTSE etc.
• Matter around us is present in the form of elements, compounds and
mixtures.
• Elements are substances containing atoms of only one type. E.g., Na, Mg,
Au, etc.
• There are 118 elements known to us. All these have different
properties.
=> Need for Periodic Classification:
• To make the study of these elements easy, these elements have been
divided into few groups in such a way that elements in the same group
have similar properties.
Now study of a large number of elements is reduced to a few groups of elements.
• Dobereiner’s Traids : When elements were arranged in the order of
increasing atomic masses, groups of three elements (known as traids),
having similar chemical properties are obtained.
The atomic mass of the middle element of the triad was roughly the average
of the atomic masses of the other two elements.
=> Newland’s Law of Octaves :
Newland arranged the then known elements in the order of increasing
atomic masses and found that the properties of every 8th element is
similar to that of the 1st element.
He compared this to the octaves found in music and called it the ‘Law of
Octaves’.
For example, the properties of lithium (Li) and sodium (Na) were found to
be the same.
Newland’s Octave:
=> Limitations :
• It was applicable upto calcium (for lighter elements only).
• Properties of new discovered elements did not fit into the law of octave.
• To fit elements into his table, Newlands put even two elements together
in one slot and that too in the column of unlike elements having very
different properties.
=> Mendeleev’s Periodic Table :
When elements are arranged in the order of increasing atomic masses, the element with similar properties occur at regular intervals.
The properties of elements are a periodic function of their atomic
masses.
Mendeleev’s periodic table is based on the chemical properties of
elements. It contains 7 periods (horizontal rows) and 8 groups (vertical columns).
Sunday, 1 October 2017
Online Notes on Chapter=4 ( Carbon and Its compounds) Part 2
This is Online Notes on Chapter=4 ( Carbon and Its compounds) Part 2 for preparation of CBSE BOARD Examination, NTSE etc=> Homologous Series:
It is series of compounds in which the some functional group substitutes for
the hydrogen in a carbon chain.
E.g., Alcohols – CH3OH, C2H5OH, C3H7OH, C4H9OH
• Have same general formula.
• Any two homologues differ by – CH2 group and difference in molecular
mass is 14μ.
• Have same chemical properties but show gradual change in physical
properties.
(i) Identify the number of carbon atoms in compounds.
(ii) Functional group is indicated by suffix or prefix.
=> Chemical Properties of Carbon Compounds:
(a) Combustion
CH4 + 2O2 ==Combution==> CO2 + 2H2O + Heat + Light
• Carbon and its compounds are used as fuels because they burn in air
releasing lot of heat energy.
• Saturated hydrocarbon generally burn in air with blue and non-sooty
flame.
• Unsaturated hydrocarbon burns in air with yellow sooty flame because
percentage of carbon is higher than saturated hydrocarbon which does
not get completely oxidized in air.
(b) Oxidation
Alcohols can be converted to carboxylic acid in presence of oxidizing agent
alkaline KMnO4 (potassium permangnate) or acidic potassium dichromate.
CH3CH2OH ==Alkaline KMnO4 or Acidic K2Cr2O7==> CH3COOH
Ethanol Ethanoic Acid
Unsaturated hydrocarbon add hydrogen in the presence of catalyst palladium
or nickel. Vegetable oils are converted into vegetable ghee using this process. It
is also called hydrogenation of vegetable oils.
(d) Substitution Reaction :
CH4 + Cl2 ==Sunlight==> CH2Cl + HCl
=> Important Carbon Compounds : Ethanol and Ethanoic acid:
Physical Properties of Ethanol:
• Colourless, pleasant smell and burning taste.
• Soluble in water.
• Volatile liquid with low boiling point of 351 K.
• Neutral compound.
Chemical Properties:
(i) Reaction with Sodium :
2Na + CH3CH2OH → 2CH3CH2O-Na+ + H2
(Sodium Ethoxide)
This reaction is used as a test for ethanol by evolution of H2 gas (Burn with
pop sound).
(ii) Dehydration :
CH3CH2OH ==Hot Conc. H2SO4==> CH2 = CH2 + H2O
Physical Properties of Ethanoic acid:
• Colourless liquid having sour taste and have smell of vinegar.
• Boiling point is 391 K.
• When pure CH3COOH is freezed, it forms colourless ice like solid. So it
is called glacial acetic acid.
Chemical Properties:
(i) Esterification :
This is saponification as soap is prepared by this.
(ii) Reaction with base :
NaOH + CH3COOH → CH3COONa + H2O
(Sod. Acetate)
iii) Reaction with carbonates and hydrogen carbonates :
2CH3COOH + Na2CO3 → 2CH3COONa + H2O + CO2
CH3COOH + NaHCO3 → CH3COONa + H2O + CO2
(Sod. Acetate)
Soaps and Detergents
• Soap is sodium or potassium salt of long chain carboxylic acid. E.g.,
C17H35COO-Na+
• Soaps are effective only in soft water.
• Detergents are ammonium or sulphonate salt of long chain of carboxylic
acid.
• Detergents are effective in both hard and soft water.
Soap molecule has :
(i) Ionic (hydrophyllic) part
(ii) Long hydrocarbon chain (hydrophobic) part
=>Cleansing Action of Soap:
• Most dirt is oily in nature and hydrophobic end attaches itself with dirt
and the ionic end is surrounded with molecule of water. This result in
formation of a radial structure called micelles.
• Soap micelles helps to dissolve dirt and grease in water and cloth gets cleaned.
• The magnesium and calcium salt present in hard water react with soap
molecule to form insoluble product called scum. This scum create
difficulty in cleansing action.
• By use of detergent, insoluble scum is not formed with hard water and
cloths get cleaned effectively.
