4. ELEMENTS , COMPOUNDS AND MIXTURES (1).pdf

Name: ___________________________________Date:__________________ Section: _____________ Roll No._______________ La Martiniere Girls’ College Class VII Che...

Name: ___________________________________Date:__________________ Section: _____________ Roll No._______________ La Martiniere Girls’ College Class VII Chemistry Chapter 4 ELEMENTS, COMPOUNDS AND MIXTURES All substances have characteristic properties which help them to distinguish one substance from another. The important physical properties of substances are: Colour Odour Taste Nature Density Solubility Melting and boiling point Chemical properties of a substance describe the characteristic ability of a substance to react to form new substances. PHYSICAL PROPERTIES OF SOME IMPORTANT SUBSTANCES: a. Colour - Solids and Gases Colour of Solids Non-metals Metals Salts Sulphur Coal/ Coke Zinc Aluminium Iron Lead Copper sulphate Chloride Yellow Dull black Greyish Silvery Dull White Blue grey Colour of Gases Colourless Oxygen, hydrogen, carbon monoxide, carbon dioxide, hydrogen chloride, nitrogen, ammonia, sulphur dioxide Coloured Chlorine (greenish yellow), nitrogen dioxide (reddish brown) b. Odourof Gases Odourless Oxygen, hydrogen, carbon monoxide, carbon dioxide, nitrogen Have Odour Hydrogen chloride, chlorine, ammonia, sulphur dioxide (pungent, choking odour) LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 1 of10 c. Taste of Gases Tasteless Oxygen, hydrogen, carbon monoxide, nitrogen Have taste Carbon dioxide, hydrogen chloride, chlorine, sulphur dioxide (slight sour taste) d. Natureof Gases Poisonous Chlorine, sulphur dioxide, ammonia, carbon monoxide. Non-poisonous Oxygen, hydrogen, carbon dioxide, nitrogen, hydrogen chloride. Acidic Hydrogen chloride, chlorine, carbon dioxide, sulphur dioxide. Basic Ammonia. Neutral Oxygen, hydrogen, carbon monoxide, nitrogen. e. Densityof Gases (with respect to air- vapour density) Lighter than air Hydrogen (lightest gas known), ammonia. Heavier than air Carbon dioxide, chlorine, sulphur dioxide. Almost as heavy Oxygen, carbon monoxide, nitrogen, hydrogen chloride f. Solubility of Gases in water Highly soluble Hydrogen chloride, ammonia, sulphur dioxide. Fairly soluble Carbon dioxide, chlorine. Slightly soluble Oxygen, hydrogen, carbon monoxide, nitrogen. g. Melting and Boiling points of solids and liquids Melting point The temperature at which solids just melt and change over to liquid. Melting point of ice is 0oC. Boiling point The temperature at which liquids just boil and change over to vapour. Boiling point of water is 100oC. h. Malleability and Ductility of metals Malleability The ability of a substance to be hammered into sheets. Examples: Copper and nickel. Ductility The ability of a substance to be drawn into wires. Examples: Goldandcopper. i. Efflorescence and Deliquescence of substances (salts) Efflorescence The ability of a crystalline substance to lose its water of crystallization to the atmosphere and change into a powder. Example: washing soda Deliquescence The ability of water-soluble substances to absorb moisture from the atmosphere and change into a solution. Example: calcium chloride LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 2 of10  PURE SUBSTANCES - ELEMENTS AND COMPOUNDS All substances as stated earlier have characteristic properties like colour, odour, nature, solubility, density, melting and boiling points. Substances may be pure or impure. Impure substances or mixtures of pure substances do not have definite characteristic properties. Pure substances are further divided into elements and compounds. SUBSTANCES PURE SUBSTANCES IMPURE SUBSTANCES ELEMENTS COMPOUNDS MIXTURES They have definite characteristic properties They have no definite characteristic properties ELEMENTS COMPOUNDS MIXTURES A pure substance made A pure substancemade up of An impure substance made up of up of one kind of atom two or morekinds of two or more kinds of atoms which cannot be broken atoms(elements)chemically (elements) orcompounds or into simpler substances. combined in a fixed bothmechanically mixed in any proportion. proportion. Examples Example Examples Na Na Cl Naa Cl H2O Sodium Sodium Chlorine Sodium chloride Water ELEMENT ELEMENT + ELEMENT COMPOUND + COMPOUND (Metallic) MIXTURE Cl Naa Cl Znn S + Zn n Chlorine ELEMENT Sodium Chloride Zinc sulphide Zinc (Non-metallic) COMPOUND COMPOUND + ELEMENT MIXTURE LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 3 of10  IMPURE SUBSTANCES – MIXTURES Mixtures contain two or more different substances mixed together in any proportion. Mixtures retain the properties of the different elements or compounds which are present in it. IMPURE SUBSTANCES MIXTURES HOMOGENEOUS MIXTURES HETERO HETEROGENEOUS MIXTURES TYPES OF MIXTURES There are two types of mixtures –homogeneousand heterogeneous HOMOGENEOUS MIXTURES HETEROGENEOUS MIXTURES Components of the mixture are uniformly Components of the mixture are not mixed throughout. uniformly mixed throughout. Composition and properties are same Composition and properties vary throughout throughout the mixture. the mixture. Examples: Examples: SALT ALCOHOL SAND OIL + + + + WATER WATER WATER WATER SEPARATION OF MIXTURES Different techniques may be used for the separation of heterogeneous and homogeneous mixtures. These include – Sedimentation and decantation Filtration Evaporation Distillation LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 4 of10  SEDIMENTATION AND DECANTATION Principle: Based on separation of insoluble solid from liquid component in a solid-liquid mixture.The insoluble solid settles down and the liquid component is decanted out. MIXTURE SEDIMENTATION DECANTATION Separation of a mixture of- On allowing the mixture to On pouring the upper layer- Insoluble solid (heavy) stand- Solid (sediment) remains constituent from its liquid Solid settles down and liquid behind and liquid (decant) is constituent collects above it poured out ❖ EVERYDAY APPLICATIONS Muddy water mixture Sand and water separation Separating mixture of chemicals FILTRATION Principle: Based on the separation of mixture of insoluble solid particles from liquid component in a solid- liquid mixture. The insoluble solid is filtered out using filter paper. MIXTURE THE FILTRATION FILTER PAPER Separation Folding and Separation on of a mixture placing the filtration- of- paper- Solid Insoluble The filter (residue) solid (light) paper is remains on the constituent made into a filter paper from its cone and this and liquid liquid cone is then (filtrate) constituent placed in the collects in the funnel as beaker below. shown FILTRATION LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 5 of10 ❖ EVERYDAY APPLICATIONS Coffee filter Tea-bags Water filters EVAPORATION Principle: Based on separation of soluble solid from liquid component in a solid-liquid mixture. The solid remains behind on evaporation of liquid component. MIXTURE EVAPORATION Separation of On heating the mixture in a mixture of an evaporating dish –Soluble placed on a wire gauze solid Solid component remains constituent behind in the evaporating from its dish and liquid liquid component is lost to the constituent atmosphere. ❖ EVERYDAY APPLICATIONS Hot tea getting cold Wet clothes drying in the sun Drying of wet hair Drying of mopped floor DISTILLATION Principle:Based on separation of soluble solid from liquid component in a solid-liquid mixture. The liquid component evaporates on heating and is re-condensed, solid component remains behind. LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 6 of10  Mixture Distillation Separation of a mixture of- On heating the mixture in the distillation flask Soluble solid constituent from Solid component remains in the distillation flask its liquid constituent. and the liquid component remains in the receiver after condensation through the condenser. ❖ EVERYDAY APPLICATIONS Extraction of pure water from salt water Desalination - separation of salt from sea water Liquefaction of gases from the air such as oxygen, nitrogen, carbon dioxide EXERCISES 1. Define the following a. Efflorescence b. Deliquescence 2. Give one difference between the following on the basis of the hint given in the bracket: a. Element and Compound (definition) b. Homogeneous mixture and Heterogeneous mixture (composition and properties) 3. Give the principle of the following method of separation of mixtures: a. Sedimentation and decantation b. Filtration c. Evaporation d. Distillation. 4. Classify the following as Element, Compound or Mixture: a. Water b. Silver c. Sodium chloride d. Iron + Sulphur e. Copper f. Air g. Sugar h. Pizza 5. Which of the following represent a compound? a. Sodium sulphide b. Sodium sulphide solution c. Sodium 6. Copper sulphide can be further subdivided into simpler substances by chemical means only. Therefore, it is an a. An element b. A compound c. A mixture LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 7 of10 Name: ____________________________________Date: ________________ Section: _____________ Roll No.: _____________ La Martiniere Girls’ College Class VII Chemistry Chapter 4 ELEMENTS, COMPOUNDS AND MIXTURES A_______________________________________________________________ B_______________________________________________________________ C_______________________________________________________________ D_______________________________________________________________ E_______________________________________________________________ F_______________________________________________________________ LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 8 of10 Name: ____________________________________Date: ________________ Section: _____________ Roll No.: _____________ La Martiniere Girls’ College Class VII Chemistry Chapter 4 ELEMENTS, COMPOUNDS AND MIXTURES A_______________________________________________________________ B_______________________________________________________________ C_______________________________________________________________ D_______________________________________________________________ E_______________________________________________________________ F_______________________________________________________________ LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 9 of10 Name: ____________________________________Date: ________________ Section: _____________ Roll No.: _____________ La Martiniere Girls’ College Class VII Chemistry Chapter 4 ELEMENTS, COMPOUNDS AND MIXTURES LMGC/CL 7/CHEMISTRY/Ch.No. 4 Page 10 of10