Everything around us is categorised into either metals or nonmetals. Hence, it is important to know what nonmetals and metals are and how to distinguish them. Metals are substances that are usually solid and have characteristics like malleability, ductility and are generally good conductors of heat and electricity. Nonmetals, on the other hand, do not show any of the characteristics of metals. The MSBSHSE Class 8 solutions of Science Chapter 7 discusses the various physical and chemical properties of metals and non-metals.
Maharashtra Board Class 8 Science Chapter 7 covers all the textbook questions of Class 8 Science. Students can use these solutions as a guide, while preparing for their exam. It helps to clear doubts and teaches them the correct methodology to write answers in their final exams.
MSBSHSE Class 8 Science Chapter 7 Objective Questions: Textbook Important Questions and Solutions
MSBSHSE Class 8 Science Chapter 7 Textbook Exercise Questions
Q1. Complete the table
|Property of Metal||Use in everyday life|
|Conduction of heat||Silver|
|Conduction of electricity||Aluminum, Iron|
Q2. Identify the odd term
a. Gold, silver, iron, diamond
b. Ductility, brittleness, sonority, malleability
c. Carbon, bromine, sulphur, phosphorus
d. Brass, bronze, iron, steel
Answer a: Diamond – It is a nonmetal, rest are metals.
Answer b: Brittleness – It is a property of non metals, the rest are properties of metals.
Answer c: Bromine – it is liquid, the rest are solids.
Answer d: Iron – Rest are mixtures
Q3. Write scientific reasons.
a. The stainless steel vessels in the kitchen have a copper coating on the bottom.
b. Copper and brass vessels are cleaned with lemon.
c. Sodium metal is kept in kerosene.
Answer a: The stainless steel vessels in the kitchen have a copper coating on the bottom because copper is a good conductor of heat.
Answer b: Copper and brass vessels are cleaned with lemon because lemon contains acid and copper and brass react with acid.
Answer c: Sodium metal is kept in kerosene because sodium reacts with air and it burns so to prevent reaction it is kept in kerosene.
Q4. Answer the following.
a. What is done to prevent corrosion of metals?
b. What are the metals that make the alloys, brass and bronze?
c. What are the adverse effects of corrosion?
d. What are the uses of Noble metals?
Answer a: To prevent corrosion of metals, layers of oil, grease, varnish and paint are applied on them. Also plating with another non corroding metal is done. Iron is arrested by zinc plating. Due to these processes, the contact of metal surfaces with air is lost and corrosion cannot occur as the chemical reaction cannot occur.
Answer b: A homogeneous mixture of two or more metals or a homogeneous mixture metal with nonmetals is called alloy. Alloys are made by mixing the constituent elements in, as per the requirement. For example, the stainless steel utensils used at home are made of an alloy of iron with carbon, chromium and nickel. The alloy bronze is formed from copper and tin.
Answer c: The uses of Noble metals are:
- Gold, silver and platinum are used to prepare ornaments.
- Silver used in medicines. (It has antibacterial property).
- Gold and silver are also used to make the medals.
- Gold and silver also used to make few electronic devices.
- Platinum, palladium metals is used as catalyst.
Q5. Three experiments to study the process of rusting are given below. Observe the three test tubes and answer the following questions.
a. Why is the nail in the test tube 2 is not rusted?
b. Why is the nail in the test tube 1 rusted highly?
c. Would the nail in the test tube 3 get rusted?
Answer a: In the test tube 2 iron nail is not rusted due to cut off the supply of air by a layer of oil.
Answer b: The nail in the test tube 1 is rusted highly as it gets both air and moisture which is required for rusting.
Answer c: The iron nail in the test tube 3 is not rusted because of the calcium chloride which is moisture absorber. Hence, the nail would not get moisture for the rusting.
Q6. What are metals? Give examples.
Answer: Metals have a lustre and are hard. Wire or sheet can be made from metal. Metals are good conductors of heat and electricity. Metals lose their valence electrons to produce positively charged ions, that is, cations. Example: Gold, silver, iron, copper, aluminium, magnesium, calcium, sodium, platinum is a few metals.
Q7. What are nonmetals? Give examples.
Answer: Nonmetals are the elements which form negative ions by accepting or gaining electrons. Nonmetals usually have 4, 5, 6 or 7 electrons in their outermost shell. Example: Carbon, Sulphur, Phosphorus is a few nonmetals.
Q8. Write the physical properties of metals?
Answer: The physical properties of metals are:
- All the metals are good conductors of heat and electricity. Cooking utensils and irons are made up of metals as they are good conductors of heat.
- Ductility is the ability of the material to be stretched into a wire. This ability allows metals to be drawn into wires and coupled with their durability, find applications as cable wires and for soldering purposes. Since metals can be drawn into wires we can say that metals are ductile.
- Malleability is the property of substances which allows them to be beaten into flat sheets. Aluminium sheets are used in the manufacturing of Aircraft because of their light weight and strength. Other metal sheets are used in automobile industries, for making utensils, etc. Therefore, metals are malleable.
- Metals are sonorous because it produces a deep or ringing sound when struck by another hard object.
- Usually, all the metals have a shiny appearance but these metals can also be polished to have a shiny appearance.
Q9. Write chemical properties of metals?
Answer: The chemical properties of metals are:
- Reaction with water: Only highly reactive metals react with water and not all the metals. For example, Sodium reacts vigorously with water and oxygen and gives a large amount of heat in the process. This is why sodium is stored in kerosene so that it does not come in contact with moisture or oxygen.
- Reaction with acids: Hydrogen gas is produced when metals react with acids. For example, when zinc reacts with hydrochloric acid it produces zinc chloride and hydrogen gas.
- Reaction with bases: Not all the metals react with bases and when they do react, they produce metal salts and hydrogen gas. When zinc reacts with strong sodium hydroxide it gives sodium zincate and hydrogen gas.
- Reaction with oxygen: Metal oxides are produced when metals burn in the presence of oxygen. These metal oxides are basic in nature. For example: When magnesium strip is burned in the presence of oxygen it forms magnesium oxide and when magnesium oxide dissolves in water it forms magnesium hydroxide.
Q10. Write the physical properties of nonmetals?
Answer: Some of the physical properties of non-metals are listed below.
- Poor conductors of electricity and heat
- Non-Ductile metals
- Brittle solids
- Maybe solids, liquids or gases at room temperature
- These are not sonorous
Q11. Write chemical properties of nonmetals?
Answer: The chemical properties of nonmetals are:
Reaction with Water – Non-metal does not react with water but it is usually very reactive in air, which is why some of them are stored in water. For example, one of the highly reactive nonmetals is phosphorus and it catches fire when exposed to air. That is why it is stored in water to prevent its contact with atmospheric oxygen.
Reaction with Acids – None of the non-metals is known to react with acids.
Reaction with Bases – The reaction between non-metals and bases is a very complex one. The reaction of chlorine with bases like sodium hydroxide gives products like sodium hypochlorite, sodium chloride as well as water.
Reaction with Oxygen – Oxides of non-metals are formed when it reacts with oxygen. The oxides of non-metals are acidic or neutral in nature.
When sulphur reacts with oxygen, we get sulphur dioxide.
S + O2 → SO2
When sulphur dioxide reacts with water it forms sulphurous acid.
SO2 + H2O → H2SO3
Q12. Define noble metal.
Answer: Some metals like gold, silver, platinum, palladium and rhodium are noble metals. They occur in nature in the elemental state. Gold, which is100 percent pure is called 24 carat gold. Pure gold is soft. As a result, the ornaments made from pure gold bend or break due to pressure. Therefore, goldsmiths mix it with a certain proportion of copper or silver. Ornaments are made from 22 carat gold or gold with a still smaller carat value.
Q13. Define corrosion.
Answer: Gases in the air react with metals in the presence of moisture to form metal compounds. The metals get affected by this process and undergo what is called corrosion.
Q14. Explain uses of metals.
Answer: Metals are usually very strong, most durable and highly resistant to everyday wear and tear. As such, they have been used since ancient times for a lot of things. And even today with advances in technology and a lot of other things the uses of metals have broadened greatly. Metals even play a key role in the economy. Some of the important and popular metal uses are.
- In the Construction Industry
- In electronics
- In medicine
- Machinery, Refractory and Automobiles
- Decorative products
- Other Uses
Q15. Explain uses of non-metals.
Answer: The uses of non-metals are:
- Uses of nonmetals in our daily life – Oxygen which is 21% by volume helps in the respiration process. It is also used for manufacturing of steel and provides high temperature in the metal fabrication process. Oxygen cylinders are used in hospitals. Chlorine is useful in removing stains and colour patches as a bleaching agent. Various graded plastics and insecticides are made with chlorine. It helps in purification of water. Adding chlorine to drinking water kills the bacterias. Helium is used as an inert gas for scientific experiments. It is also used in weather balloons. Iodine helps from throat infections and is used as antiseptic on wounds and cuts.
- Nonmetals used in fertilizers – Fertilizers contain nitrogen. It helps in plant growth. It enhances the rate of plant growth. Non Metal phosphorus is also used for better plant growth. These two nonmetals play a major role in plant growth.
- Nonmetals used in crackers – sulphur and phosphorus are used in fireworks.
Q16. Difference between metals and nonmetals.
Answer: The difference between metals and nonmetals are:
|These are solids at room temperature except mercury||These exist in all three states|
|These are very hard except sodium||These are soft except diamond|
|These are malleable and ductile||These are brittle and can break down into pieces|
|These are shiny||These are non-lustrous except iodine|
|Electropositive in nature||Electronegative in nature|
|Have high densities||Have low densities|
Q17. How can we prevent corrosion?
Answer: We can prevent corrosion by the following ways:
- Choosing the right type of metal can help control corrosion and reduce the requirement for additional prevention measures. For example, metals like aluminium and stainless steel are highly resistant to corrosion.
- One of the cheapest ways to control corrosion is by applying a layer of paint on the surface of the metal. This coating of paint acts as a barrier and protects the metal from corrosion by preventing the flow of electrochemical charge.
- The control over the constituents of the environment to which the metal is exposed can also help in the prevention of corrosion. An example of this would be the treating of water with softeners before putting it in a boiler to prevent corrosion inside the boiler.
Q18. What are the three types in which the elements are generally classified?
Answer: The three types in which the elements are generally classified are solids liquids gases
Q19. What are the metals and nonmetals that we use in everyday life?
Answer: Some non – metals and their uses are listed below-
- Oxygen is used for breathing.
- Chlorine is used for purifying water.
- Non – metals like nitrogen, is used in fertilizers.
- Graphite is used as a good conductor of electricity.
- Potassium is used in fertilizers.
Some metals and their uses are listed below:
- Gold and silver are used for making jewellery.
- Copper is used for making electrical wires, cooking utensils etc.
- Zinc is mainly used as a protective coating for iron.
- Aluminium is used for making electrical cables, packaging, cooking utensils, etc.
- Metals like iron and steel are widely used in building and home constructions.
Q20. What are non metal materials?
Answer: nonmetals are natural materials that do not produce heat or electricity and that are structurally brittle (can not be easily rolling, moulding, extruding or pressing). Chemically, hydrogen, carbon, nitrogen, oxygen, phosphorus, arsenic, and selenium are the nonmetallic elements in the periodic table.