A brown substance ‘X’ on heating in air forms a substance ‘Y’. When hydrogen gas is passed over heated ‘Y’, it again changes back into ‘X’. (i) Name the substance ‘X’ and ‘Y’. (ii) Name the type of chemical reaction occurring during both the changes. (iii) Write the chemical equations of the reactions. Open Answer »
When CaO is added to water taken in a beaker, rise in temperature is observed. However, when Ba (OH) 2 is mixed NH4 Cl, a fall in temperature is observed. Why? Open Answer »
Compound ‘A’ when dissolved in water gives compound ‘B’ which used in whitewashing. Compound ‘B’ reacts with CO2 to form a white precipitate of compound ‘C’. Identify compounds ‘A’ ‘B’ and ‘C’. Also write the equations involved. Open Answer »
Justify with the help of an example that displacement reaction is also a redox reaction. Open Answer »
Samuel had a Silver coin which turned black. He kept coin in a bowl lined with aluminium foil. Then he filled the bowl with water and boiled it. After sometime, he found that the coin has become new. Its blackness disappeared. How did it happen? Open Answer »
Sheena was very excited to see her Aunt after a long time. Her mother fried a lot of snacks for her Aunt. Suddenly Sheena came to know that her aunt has postponed her plan for tomorrow. Sheena’s mother got worried to know this. She thought the food will get spoiled. Sheena helped her mother to preserve the food. Answer the following questions based on above passage. (i) Why does food spoil when kept for a very long time? (ii) What method did Sheena suggest her mother to preserve the food? (iii) What values are shown by Sheena? Open Answer »
Crystals of copper sulphate are heated in a test tube for some time. (a) What is the colour of copper sulphate crystals before heating, and after heating? (b) What is the source of liquid droplets seen on the inner upper side of the test tube during the heating process? (ii) A metal ‘X’ when dipped in aqueous solution of aluminium sulphate no reaction is observed whereas when it is dipped in an aqueous solution of ferrous sulphate, the pale green solution turns colourless. Identify metal ‘X’ with reason. Open Answer »
What happens when zinc granules are treated with dilute solution of H2SO4, HCl, HNO3, NaCl and NaOH? Also write the chemical equations if reaction occurs. Open Answer »
With the help of an activity explain that hydrogen and oxygen are released when an electric current is passed through water. Open Answer »
