1) Describe an activity with diagram to show that acidified water conducts electiricity.
2) Marble statues are often corroded when kept in open for long time. Explain
i) Activity to show that acidified water conducts electricity.
Fill a beaker half with water and add some acid to it. Two carbon rods or electrodes (made of graphite ) are placed in the acid solution in the beaker. An electric circuit is then set up by including a battery, a bulb and a switch. Now press the switch. On pressing the switch , the bulb lights up at once. If the same activity is repeated with pure water then bulb does not glow.This means that the acid solution taken in the beaker allows the electric current to pass through it. In other words , the acid solution conducts electricity.
(ii) Marble gets corroded when kept in open for long time. This is because the surface get attacked slowly by air and water in the atmosphere. At some places (specially in industrial areas ) there are some acidic gases in the air which mix with rain water to form acids. These acids attack the surface of statues and eat them up slowly.
For example : Taj mahal is an example of corrosion of marbles. The marble consist of carbonate compound mainly calcium carbonate (CaCO3) which is basic in nature. It reacts with the acids present in raining water due to reaction of acidic gas effluents like SO2 , NO2 etc with rain water and transformed into other substances.
CO2 + H2O H2CO3
NO2+ H2O HNO3
H2CO3 + CaCO3 Ca(HCO3)2
2 HNO3+ CaCO3 Ca(NO3)2+ H2O + CO2
The compounds formed are water soluble and are easily washed away.