Give reason for the following
1. Shining surface of metal is tarnished after some time
2. Sodium and potassium are kept under kerosene oil
3. Metals conduct electricity
4.tungsten is used for making filaments of incandescent bulbs 5. Generally noH2 gas is evolved when metals react with dilute nitric acid
Answers
Answer:1.The surface of metals undergo oxidation under the influence of air, moisture and chemicals such as acids, which is called corrosion. Because of this process, the shining surface of metals is tarnished after some time. For example, iron turns reddish brown due to corrosion and silver turns greyish due to this process.
2.Sodium and potassium metals arekept in kerosene or in dry mineral oil. Both of these metals are in Group 1 on the periodic table. All metals in that group are very reactive with water, including moisture in the atmosphere. You may have seen videos where people have thrown chunks of sodiummetal into bodies of water.
3.Metal atoms have outer electrons which are not tied to any one atom. These electrons can move freely within the structure of a metal when an electric current is applied. There are no such free electrons in covalent or ionic solids, so electrons can't flow through them - they are non-conductors.
4.Tungsten metal is selected for making filaments of incandescent lamp bulbs because it can sustain high temperatures, i.e., it has a high melting point.
5.Explanation: When metals react withnitric acid hydrogen gas is liberated.Nitric acid is a very strong oxidizing agent. So , it oxidizes the hydrogen gasformed during the reaction to form water and an oxide of nitrogen ( NO,N2O,NO2 etc.
Explanation: