7.14 MHCERT 7th General Science 14. Elements, compounds and mixtures

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MHCERT - General Science - chapter 14. Elements, Compounds and Mixtures



Que. 1 

Who is my companion?

1. Stainless steel-alloy

2. Silver-metal

3. Bhajani mixture 

    for milling-a mixture

4. Salt-compound

5. Coal-element

6. Hydrogen -non-metal

2. Write the names of elements from the following symbols : 

Cd - cadmium

Xe - xenon

Br - bromine

Ti - titanium

Cu - copper/ cuprous 

Fe - iron/ Ferrum

Si - silicon

Ir - iridium

Pt - platinum


3. What are the molecular formulae of the following compounds?

Hydrochloric acid - HCl

Sulphuric acid - H2SO4

Sodium chloride - NaCl

Glucose - C6 H12O6

Methane - CH4


4. Give scientific reasons.

(a) Buttermilk is churned to get butter.

Ans.

  1. Buttermilk is a mixture. 
  2. The small particles of butter are dispersed in the buttermilk. 
  3. They get aggregated due to centrifugal force during churning and form a lump. As fats are lighter than water butter floats on the buttermilk and can be separated easily. 
  4. So buttermilk is churned to get butter.

 (b) In chromatography, the ingredients of a mixture rise up to a limited height when the water rises up to the upper end of the paper.


  1. The mixture used in the experiment of chromatography has two substances that have mutually opposite properties. 
  2. One substance (water) moves up rapidly and the other substance has the property to stick to the filter paper. 
  3. So, the water rises with speed but the solute does not rise with that speed. 
  4. So, the ingredients of a mixture in chromatography rise up to a limited height when the water rises up to the upper end of the paper. 


(c) A wet cloth is wrapped around a water storage container in summer.

 Ans.

  1. The moisture in the wet cloth evaporates during the summer season. 
  2. During the evaporation, it absorbs some amount of heat from the water in the container. 
  3. Thus it becomes cooler. 
  4. To make the water in the container cooler, a wet cloth is wrapped around the water storage container in summer.

5. Explain the difference.


(a) Metals and non-metals 

Metals

  1. Metals have lustre. 
  2. Metals are malleable. 
  3. Metals are ductile. 
  4. Metals are good conductors of heat and electricity. 
  5. At normal temperatures, metals are in a solid state. (exception Mercury)
  6.  Normally metals have a high density. 
  7. For example, gold, silver, mercury.

Non-metals

  1. Non-metals do not have lustre. 
  2. Non-metals are not malleable. 
  3. Nonmetals are not ductile. 
  4. Non-metals are not good conductors of heat and electricity. 
  5. At normal temperatures,  nonmetals are either in solid-state or in a gaseous state. (exception bromine) 
  6.  Normally non-metals have less density. 
  7. For example oxygen, hydrogen.


 (b) Mixtures and compounds 

Mixtures

  1. A mixture is obtained by just mixing two or more substances with any properties in any proportion. 
  2. A mixture can be further subdivided into similar substances by simple physical processes. 
  3. The constituents of a mixture retain their original properties. 
  4. For example,  seawater, sherbet 

Compounds

  1. A compound is made of two or more elements chemically combined in a fixed proportion. 
  2. A compound can be further subdivided into simpler substances by chemical means only. 
  3. The properties of a compound are entirely different from the properties of its constituents. 
  4. For example, common salt, sugar, water etc.


(c) Atoms and molecules 

Atoms

  1. The smallest particle of an element is called an atom. 
  2. An atom cannot be subdivided. 
  3. When atoms come together a molecule is formed. 
  4. An atom is not stable by itself.

Molecules

  1. The smallest particle of a compound is called a molecule. 
  2. Molecules are formed by the combination of two or more atoms.  
  3. Molecules can be subdivided into individual atoms. 
  4. A molecule is usually stable to exist by itself.

(d) Separation by distillation and by Separating funnel

Separation by distillation -



1. The method of distillation is used to separate the solid solute from the liquid.

2.  Heat is given during the separation.

By Separating funnel -



1. For the separation of two immiscible liquids, the method of separating funnel is used. 

2. It requires a separating funnel.

6. Write answers to the following questions in your own words.

(a) How are the components of mixtures separated by simple methods?


 Following simple methods are used to separate insoluble substances from the solution. 

  1. Sifting - to separate solids of various shapes or sizes.
  2. Picking - to separate substances that are needed or not needed.
  3. Winnowing - to separate substances that are lighter in weight like husks in grains.
  4. Magnet - to separate magnetic substances from non-magnetic substances.
  5. Sublimation - to separate the sublimatory substances like camphor and iodine.

(b) Which elements (metals and non-metals), compounds and mixtures do we use in our day-to-day life?

We use metals like iron, gold, silver, copper, brass, steel etc. in day to day life.

We use the mixtures like tea, coffee, bhel, sharbat, stainless steel, brass etc. in day to day life. 

We use the compounds like sugar, saltwater, washing soda etc. in daily life.


(c) In everyday life, where and for what purpose do we use centrifugation?

In everyday life, we use a churner to separate butter from buttermilk by the centrifugation method. The smaller size particles of butter can be separated by centrifugal force.


(d) Where are the methods of separation by distillation and by separating funnel used? Why?

It is used to separate dissolved salts or impurities from the solution. 

We can separate salt from seawater by the method of separation by distillation. 

By using a separating funnel we can separate the immiscible liquids like kerosene and water.


(e) Which precaution will you take while using the methods of distillation and separation by the separating funnel?

In distillation, the apparatus should be properly set up. The distillation flask should be carefully heated. The condenser tube should be properly cooled. 

In the separating funnel, the stopcocks should be manipulated, otherwise, it releases the liquid inadvertently.

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11. Cell Structure and Micro-Organisms

https://eeducationplusall.blogspot.com/2022/02/cell-structure-and-micro-organisms.html

12. Muscular System and Digestive System  in Human Beings

https://eeducationplusall.blogspot.com/2022/02/mhcert-7th-science-12-muscular-system.html

13. Changes - Physical and Chemical

https://eeducationplusall.blogspot.com/2022/02/mhcert-science-13-changes-physical-and.html

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