Selina Concise Class 8 Chemistry Solution Chapter No. 3- ‘Elements, Compounds and Mixtures’ For ICSE Board Students.
1)
a) Element :
The substance which is made up of same kind of atom are called element.
Or
Elements is the substance which can not break into simpler one.
b) Compound :
When two or more elements chemically bonded together and formation of molecules occur are called compound.
2)
a) Metal:
Answer : Example of metals are Gold, silver , aluminium , iron , copper, etc.
b) Non – Metal:
Answer : example of Non-Metals are Hydrogen , Nitrogen , Carbon , Oxygen etc.
c) Metalloid :
Answer : example of Metalloids are Germanium , silicon , arsenic , Boron etc.
d) Inert gases :
Answer : Helium , , Neon , Argon. , Xenon , etc.
3)
a)
Sr .no | Pure substance | Impure substance |
1 | Pure substance are made up of one type of constituent or composition. | Impure substance are made up of different types of constituent or composition. |
2 | Pure substance have same chemical and physical properties . | Impure substance May be different chemical and physical properties. |
3 | Pure substance or composition have fixed proportion. | Impure substance or composition are varying proportion. |
4 | Pure substance can not separate from simple physical method. | Impure substance can be separated from simple physical method. |
5 | Example: gold metal , NaCl ( table salt) etc. | Example : sea water , petroleum , air etc. |
b)
Sr .No | Homogeneous substance | Heterogeneous substance |
1 | Same kind or uniform composition of a substance are known as homogeneous substance | Different kinds or not uniformly composition of a substance known as heterogeneous substance. |
2 | It has fixed proportion | Heterogeneous mixture has not in fixed proportion |
3 | Homogeneous substance can not be separate easily. | Heterogeneous substance can be separate easily |
4 | Example : tap water , air etc. | Sand and water , oil and water etc. |
4)
a) Baking soda
Ans : Chemical Name : sodium bicarbonate
Chemical Formula: NaHCO3
b) Vinegar
Ans : Chemical Name : Acetic acid
Chemical Formula : CH3COOH
c) Marble :
Ans : Chemical Name : Calcium Carbonate
Chemical Formula : CaCO3
d) Sand :
Ans: Chemical Name : Silicon dioxide
Chemical Formula : SiO2
5)
a) A soft metal:
Ans : sodium and potassium are soft metal .
b) A metal which is brittle :
Ans : zinc is a metal which is brittle.
c) A non metal which is lustrous :
Ans : iodine and graphite is a non metal which is lustrous.
d) A liquid metal:
Ans : mercury is a liquid metal.
e) A metal which is a poor conductor of electricity :
Ans : Tungsten is a metal which is poor conductor of electricity.
f) A non metal which is good conductor of electricity :
Ans : graphite is a good conductor of electricity.
g) A liquid non metal :
Ans : Bromine is a liquid non metal.
h) A hardest naturally occurring substance :
Ans: Diamond is a hardest Naturally occurring substance
i) An inert gas.
Ans : Helium, Neon, Argon are inert gases.
6)
Answer : Sodium chloride compound are totally different nature, from sodium and chlorine , sodium is highly reactive with Air and water that’s why it is stored in kerosene, and chlorine is very Poisonous gas . When these two elements chemically react with each other to form sodium chloride , it ,is commonly known as table salt which is used in a food in daily basis.
7)
Answer : Iron sulphide (FeS) is a compound because when iron and Sulphur get heat together both chemically react each other and from iron sulphide , it can be broken into iron and Sulphur which totally different properties from its compound.
Exercise: Part -B
1)
Answer:
a) Carbon dioxide:
Carbon dioxide is a compound which is made up of elements carbon and oxygen.
b) Air :
Air is a mixture, in which different type of gases like Nitrogen, oxygen , carbon etc and water vapour , dust particles etc It can be separate by physical method like fractional distillation.
c) Water :
Water is a compound which is made up elements Hydrogen and oxygen.
d) Milk :
Milk is a mixture because so many constituents are present in it like fat , water , protein , lactose , caseins etc .
e) Common salt :
Common salt is a compound , chemical name of common salt is sodium chloride which is made up of sodium and chlorine elements .
f) Blood :
Blood is a mixture which is homogeneous , blood made of different types of components. We can separate this component by physical method.
g) Fruits juice :
Fruits juice is a mixture , it contains many type of constituents like sugar , water , glucose , sucrose etc.
h) Iron sulphide:
Iron sulphide is a compound . It is made up of iron and Sulphur elements which can be separate easily.
2)
a) . Solid solid homogeneous mixture:
Answer : Example :brass, bronze.
b) . Solid solid heterogeneous mixture:
Answer: Example: common salt and sand.
c) .Miscible liquid:
Answer: Example : kerosene and water , oil and water.
d) .Liquid gas homogeneous mixture:
Answer :Example : ammonia and water , water and carbon dioxide.
3) a)
Answer : Salt from sea water :
Evaporation technique used in Separation of salt from sea water , because evaporation is the process to separate the solid liquid homogeneous type of mixture , in this technique when water is evaporate only solid substance means salt is left that’s of used this technique.
b)
Answer: Ammonium chloride from sand :
Sublimation technique used in the separation of ammonium chloride and sand , because sublimation is process where solid mixture give heat directly and convert it into its vapour, after get cooling environment this vapour deposit as solid , in ammonium chloride and sand mixture , ammonium chloride directly converted into vapour after give heat and sand is left , after cooled environment ammonium chloride deposit directly as solid.
c)
Answer : Chalk powder from water :
Filtration technique used in the separation of chalk powder from water , in this process insoluble substance (solid ) are filtrate from a liquid . Chalk powder are insoluble in water so by the technique filtration we can easily separate this mixture .
d)
Answer: Iron from sulphur :
Magnetic separation technique used in the separation of iron and Sulphur , because iron is a magnetic in nature , iron attract toward the magnet ,by this process we can easily separate iron and Sulphur mixture.
e) .
Answer : Water and alcohol :
Fractional distillation technique used in Separation of alcohol and water because fractional distillation is the process where two different boiling point liquid mixture which is homogeneous or miscible can easily separate out . The boiling point of alcohol is 78°C and boiling point of water is 100°C so we can easily separate the mixture of alcohol and water from this technique.
e)
Answer : Sodium chloride and potassium nitrate :
Fractional crystallization technique used in the separation of sodium chloride and potassium nitrate , because it this technique different solubility of solid substance Can be easily separateout, in this mixture both component are soluble in water but potassium nitrate is more soluble as compared to sodium chloride so , we can separate this mixture from fractional crystallization technique .
f)
Answer : Calcium Carbonate and sodium chloride:
Solvent extraction technique used in the separation of calcium carbonate and sodium chloride because in the solvent extraction technique mixture of solid solid , one of the components is soluble in any solvent and other are not so mixture of calcium carbonate and sodium chloride , sodium chloride is soluble in water and calcium carbonate left so we can easily separate out this mixture from this technique.
4) a) Answer : Mixture :
Mixture is a combination of two or more different pure substance .
b) Answer: It is necessary to separate the constituent of a mixture, because to remove the impurities and contamination from the mixture , and to get pure and desirable things or substance.
c) Answer :
Sr .No | Compound | Mixture |
1 | Compound are made up of mixed ratio or proportion. | Mixture has not any fixed ratio or proportion |
2 | Compound are chemically bonded | Mixture are not chemically bonded |
3 | The whole compound have same properties | The whole mixture has not same properties. |
4 | Boiling and melting point are same. | Boiling and melting point are variable. |
5 | It can not be separate from simple physical method. | It can be separate from simple physical method. |
5) a)
Answer : Chromatography :
Chromatography is a separation technique in which identical properties of mixture is separate by Mobilephase , or solvent ( liquid or gas ) is run on the stationary phase or fixed phase. It is used for homogeneous mixture or identical properties of mixture in different solubility of constituent . For example coloured dye .
b)
Answer : Advantage of Chromatography:
- Many components of mixture can be identified form chromatography technique.
- Very minimum quantity of mixture can be separate from this method .
- Analysis are fast through this component.
- Fine or homogeneous mixture can be separate from thus technique.
c)
Answer : Application of chromatography :
- To identify alcohol from patients blood .
- To purify Protein.
- Identify the chemical in new product in a pharmaceutical industry.
- Test for contamination in environment.
6)
a) A mixture of sand and ammonia chloride can be separated by
Answer: (iii) Sublimation
Explanation: sublimation is process where solid mixture give heat directly and convert it into its vapour, after get cooling environment this vapour deposit as solid , in ammonium chloride and sand mixture , ammonium chloride directly converted into vapour after give heat and sand is left , after cooled environment ammonium chloride deposit directly as solid.
b) Pair of Metalloids are hloride
Answer : (ii) B and Si
Explanation: Boron (B ) and Silicon (Si) are metalloid because these have the Properties of metal and non metal also.
c) Which of the following property is not shown by compound?
Answer : (i) They are Heterogeneous
Explanation: Compound are pure and homogeneous substance , they have fixed proportion and fixed boiling and melting point that’s why compounds are not Heterogeneous.
d) A solvent of iodine is
Answer : (iii) Alcohol
Explanation: Alcohol uses as a solvent of iodine because iodine is readily soluble in alcohol.
e) This gas is highly soluble in water.
Answer : (i) Ammonia
Explanation: Ammonia is highly soluble in water because it may be possible through hydrogen bonding between Ammonia and water molecule.