3. Metals and Non-metals Science class 10 in English Medium ncert book solutions Chapter Review

Chapter Review:

• Metals, in their pure state, have a shining surface. This property is
  called metallic lustre.
• Some metals can be beaten into thin sheets. This
  property is called malleability.
• The ability of metals to be drawn into thin wires is called ductility.
• Gold is the most ductile metal a wire
  of about 2 km length can be drawn from one gram of gold.
• The metals that produce a sound on striking a hard surface
  are said to be sonorous.
• The best conductors of heat are silver and
  copper. Lead and mercury are comparatively poor conductors of heat.
• Full Form of PVC is polyvinylchloride.
• Gallium and caesium have very low melting points.
• Iodine is a non-metal but it is lustrous.
• Diamond, an allotrope of carbon, is
  the hardest natural substance known and has a very high melting
  and boiling point.
• Graphite, another allotrope of carbon, is a conductor of electricity.
• Lithium, sodium, potassium are so soft that they can be cut with a knife. They have low densities and low melting points.
• Metals such as potassium and sodium react so vigorously that they catch fire if kept in the open.Therefore they are kept immersed in kerosene oil.
• Anodising is a process of forming a thick oxide layer of aluminium.
• Aqua regia is a freshly prepared mixture of concentrated hydrochloric acid and concentrated nitric acid in the ratio of 3:1.Aqua regia is a highly corrosive, fuming liquid.
• The metals at the top of the activity series (K, Na, Ca, Mg and Al) are so reactive that they are never found in nature as free elements.
• The metals in the middle of the activity series (Zn, Fe, Pb, etc.) are moderately reactive. They are found in the earth’s crust mainly as oxides, sulphides or carbonates.
• Ores mined from the earth are usually contaminated with large amounts of impurities such as soil, sand, etc., called gangue.
• Cinnabar (HgS) is an ore of mercury.
• The sulphide ores are converted into oxides by heating strongly in the presence of excess air. This process is known as roasting.
• The carbonate ores are changed into oxides by heating strongly in limited air. This process is known as calcination.
• Galvanisation is a method of protecting steel and iron from rusting
  by coating them with a thin layer of zinc.
• The rusting of iron can be prevented by painting, oiling, greasing,
  galvanising, chrome plating, anodising or making alloys.
• When iron is mixed with nickel and chromium, we get stainless steel, which is hard and does not rust.
• An alloy is a homogeneous mixture of two or more metals, or a metal and a non-metal.
• Pure gold, known as 24 carat gold, is very soft. It is, therefore, not suitable for making jewellery.
• The alloy of mercury is known as an amalgam.
• The extraction of metals from their ores and then refining them for use is known as metallurgy.