Selina Concise Class 6 Chemistry Chapter 4 Elements Compounds Symbols and Formulae Solution

Selina Concise Class 6 Chemistry Solution Chapter No. 4- ‘Elements Compounds Symbols and Formulae’ For ICSE Board Students.

EXERCISE-I

(1.) CLASSIFY THE FOLLOWING SUBSTANCES INTO ELEMENTS AND COMPOUNDS.

ANS:- COMPOUND:- Sugar, water,  Alchohol , Sand.

ELEMENT:- Mercury, Sulphur, Gold, Coal, Oxygen.

(2.) GIVE THE SYMBOLS OF:- CARBON, CALCIUM, COPPER, CHLORINE, COBALT, ARGON.

ANS:- Carbon is C  .     Chlorine is Cl.       Calcium is Ca.

Copper is Cu.      Cobalt is Co.         Argon is Ar.

(3.)  DEFINE A PURE SUBSTANCE . NAME THE TYPES OF PURE SUBSTANCES UOY KNOW.

ANS:- A substance of a definite composition which has consistent properties through out is called a pure substance.

Pure substances are two types:- i) elements. Ii) Compounds.

(4.) DEFINE- a) ELEMENTS. b) COMPOUNDS

ANS:- Elements:- An element is defined as a pure substance made up of only one kind of atoms that cannot be converted into anything simpler than itself by any physical or chemical process.

COMPOUNDS:- Compounds are pure substances composed of two or more elements in definite proportion of mass and has a definite set of properties. Compound is made up of only one kind of molecules.

(5.) GIVE TWO EXAMPLES OF EACH OF THE FOLLOWING:-

a) METALS:- Silver, gold. b) NON METALS:- Carbon, Sulphur.

c) METALLOIDS:- Antimony, silicon, boron.

d) NOBLE GASES:- Helium, Neon, Argon.

(6) NAME THE ELEMENTS WHICH FORM WATER . STATE THREE CHARACTERISTICS  OF WATER TO JUSTIFY THAT IT IS A COMPOUND.

ANS:- The elements which form water are Hydrogen and water.

Three characteristics of water to justify that it is a compound:-

(1.) Water is formed when the two elements of hydrogen and oxygen . Water has entirely different properties from the element it is made up of .

(2.) Energy is needed to form water on combining  O2 and H2.

(3.) We cannot separate the constituents of water by simple physical means.

(7) GIVE THREE DIFFERENCES BETWEEN METALS AND NON METALS.

ANS:- Three differences are-

a) Metals are ductile that is it can be drawn into wires.

Non metals are mostly soft solids cannot be drawn into wires.

b) Metals are malleable that is it can be beaten to form sheets.

Non metals are mostly gases and are not mellable.

C) Metals are sonorous.

Non metals do not produce sounds when stuck.

(8) STATE FOUR IMPORTANT CHARACTERISTICS OF COMPOUNDS.

ANS:-  Characteristics are- 1. When compound is formed energy like heat, light or electricity is either needed or produced.   2. A compound has properties entirely different from the properties of its constituents.    3. Change in weight take place.    4. It cannot be separated into its constituents by simple physical means.

(9) HOW IS SODIUM CHLORIDE IS DIFFERENT FROM ITS CNSTITUENTS ELEMENTS, SODIUM AND CHLORIDE IN ITS PROPERTIES? JUSTIFY.

ANS:- Sodium is a metal that is stored in kerosene oil as its reacts very fast with air and water. Chlorine is a reactive greenish yellow gas which is poisonous. When these two elements combine chemically they form common salt sodium chloride which is non poisonous colourless solid substance that we use in our food to add taste and to obtain some nutrition.

(10) GIVE TWO EXAMPLES FOREACH OF THE FOLLOWING:-

a) Non metals which are solids- sulphur, Phosphorus.

b) METALS WHICH ARE SOFT- sodium and lead

c) NON METALS WHICH ARE LUSTROUS:- Radium, Graphite.

d) ELEMENTS WHICH ARE LIQUID:- Bromine, mercury.

e) INERT GASES:- Helium, argon.

(11) NAME THE ELEMENTS PRESENT IN THE FOLLOWING COMPOUNDS:-

a) Sugar:- Carbon, hydrogen and oxygen

b) Ammonia:- Nitrogen and hydrogen.

c) MARBLE:- Calcium, Carbon, oxygen

d) Washing soda:- Sodium, Carbon, Oxygen

(12) WHAT IS THE NPROPORTION OF ELEMENTS PRESENT THE FOLLOWING COMPOUNDS:-

                               ELEMENTS proportion of elements.
a)H2O H:O 1:8
b) Co2 C:O 3:8
c) CaO Ca:O 5:2
d)  NO2 N:O 7:16

EXERCISE-II

(1.) DEFINE:-

a) ATOM:- An atom is is the smallest indivisual unit of element which exhibits all the proprties of that element or may not have independent existence.

b) MOLECULE:- A molecule can be defined as the smallest unit of an element or a compound which exhibits all the properties of that element or compound and has independent existence. They are divisible into atoms.

c) ATOMICITY:- The number of atoms in a molecule of an element is called its atomicity.

d) FORMULA:- Formula is a short way of representing the molecule of an element or a compound.

(2.) WHY ARE SYMBOLS AND  FORMULAE OF SUBSTANCES IMPORTANT?

ANS:- Symbols and formulae of substances gives a lot of substance gives a lots of information-

i.) Types of elements present in the compound.  ii) Number of each kind of atoms in one molecule.      Iii) Mass of one molecule of the compound.

(3.) MENTION THREE GASEOUS ELEMENTSB AND WRITE THEIR MOLECULAR FORMULAE.

ANS:- Three gases elements are Hydrogen, Oxygen, Chlorine.

Molecular formulae: – H2, O2, Cl2

Atoms in one molecule all: – 2

(4.) STATE THE INFORMATIONS OBTAINED FROM THE FORMULA OF A COMPOUND.

ANS:- A formula gives us the following information about a compound.

1.) Types of elements present in the compound.

2.) Mass of one molecule of the compound.

3.) Number of each kind of atoms in one molecule of the compound.

(5)  THE DIFFRENCE BETWEEN THE FOLLOWING:-

a) 2H AND H2

ANS:- 2H atoms of hydrogen. H2 is one molecule of hydrogen gas.

b) H2O and 3H20:-

ANS:- H2O represents one molecule of water. 3H2O represents 3 molecules of water.

(6) STATE THE NUMBER OF ATOMS OF EACH ELEMENT PRESENT IN-

a) C6H12O6:- Carbon- 6 atoms in number.

Hydrogen- 12 atoms in number.

Oxygen- 6 atoms in number.

The name of the compound is Glucose.

b) H2SO4:- Hydrogen:- 2atoms in number.

Sulphur:- 1 atom in number.

Oxygen:- 4 atoms in number.

The name of compound is sulphuric acid.

c) HNO3:- Hydrogen- 1 atom in number.

Nitrogn- 1 atom in number.

Oxygen- 3 atoms in number.

The name of the compound is nitric Acid.

d) CACO3:- calcium:- 1 atom in number.

Carbon-  1 atom in number.

Oxygen-   4 atoms in number.

The name of compound is Calcium Carbonate.

(7) Write the molecular formulae of compounds calcium oxide, hydrogen sulphide, carbon monoxide and lead sulphide.

Ans:-

(8) GIVE TWO EXAMPLES EACH OF THE COMPOUNDS EXISTING IN THE FOLLOWING STATES:-

a) SOLID:- NaCl, SiO2

b) LIQUID:- H2O, HCl

c) GASEOUS:- CO2,

EXERCISE-III

(1.) A) THREE DIFFERENT FORMS OF CARBON.

ANS:- 1. Coal    2. Graphite.     3.Diamond

b) A FORM OF CARBON USED AS AGEM.

ANS:- Diamond is used as a gem.

c) TWO SUBSTANCES USED TO MAKE ELECTRIC WIRES.

ANS:- 1.Copper.

  1. Aluminium.

d) TWO SUBSTANCES USED TO MAKE JEWELLERY.

ANS:- 1. Gold.  2. Silver.

e) A SUBSTANCE USED AS AN INSULATOR.

ANS:- Plastic.

(2.) GIVE ONE USE OF EACH OF THE FOLLOWING:-

a) Iron:- To make machines and building material.

b) Brass:- To make water taps and utensils.

c) Coal:- Coal is used as fuel and also it is used in thermal power plant to produce electricity.

(3.) GIVE REASON-

A) A FRYING PAN IS MADE UP OF STEEL BUT ITS HANDLE IS MADE UP OF WOOD.

ANS:- Steel is good conductor  of heat to cook food, pan is made of steel where as wood is an insulator of heat and to hold , handle is made up of wood.

b) GRAPHITE IS USED TO MAKE LEAD OF THE PENCILS.

ANS:-  Graphite leaves mark on the paper and makes it black. So it is used to make pencils lead.

c) ARGON IS FILLED IN ELECTRIC BULBS.

ANS:- Argon is inert gas and protect the element of bulb from oxidation and burning. Hence increase bulbs life.

(4)

a) WHY ARE COPPER AND ALUMOINIUM USED TO MAKE ELECTRIC WIRES.

ANS:- Because Copper and aluminium are good conductors of heat and electricity. They can be drawn into wires and beaten into sheets. Therefore, they are used to make electric wires.

b) WHAT DO YOU UNDERSTAND BY THE STATEMENT:-“ METALS ARE DUCTILE AND MALLEABLE”

ANS:-  Metals are ductile that means they can b drawn or stretched into thin wires. They are malleable that is they can be beaten into thin sheets.

Updated: June 13, 2020 — 12:07 am

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