3. Give reason why for the following-
3a. Nitrogen is used in flushing food packages.
3b. Patients suffering from lung problems are kept in an oxygen tent.
3c. Halogens and noble gases are placed in separate groups of the periodic table.
4. Give a balanced equation for addition of iron to copper [II] sulphate solution. State the change
in colour seen.
5. A chemical reaction is generally accompanied by certain external indications or characteristics.
Give any two characteristics.
6. Name any three components of air and their percentage in the air.
7. How would you prove that different components of air have variable composition from place
to place give one example.
8. State the utility of carbon dioxide for the manufacture of food by plants
Answers
Answer
3a. Nitrogen is an inert gas and does not react with oil and fats. ... thus bags used in packaging food items are flushed with nitrogen gas to remove oxygen inside the pack. when oxygen is not present inside the packet rancidity of food item is avoided.
3b. (a) Patients suffering from lung problems are kept in an oxygen tent because they require artificial supply of oxygen. (b) Oxygen finds utility in welding & cutting of metals because of oxy-acetylene and oxy-hydrogen flame provides temperature around 3000 degree celsius and 2800 degree celsius.
3c. Halogens are extremely reactive elements because they need one more electron to gain a full octet state while noble gases are extremely unstable because they already have their full octet state, hence they are placed in separate groups of the periodic table.
4. When Iron nail (Fe) kept in Copper sulphate (CuSO4) there takes reaction between them. As Iron is more reactive than Copper it can replace Copper from CuSO4. CuSO4 is in blue Colour and FeSO4 is in light green colour. So, there will be change in the composition and colour of the solution (from blue to light green).
5. Change of colour — In certain chemical reactions a change of colour is seen to be observed. Heat on substances to observe change in colour of reactants and products.
6. Composition of air is:
Nitrogen - 78%
Oxygen - 21%
Carbon dioxide - 0.03 %
Inert gases - 0.9%
7.
8. State its role in warming the earth's environment and in excess resulting in global warming. Solution: In photosynthesis, green plants manufacture their own food by absorbing carbon dioxide in the air and make food in the presence of chlorophyll and sunlight. ... It results in warming the earth's environment.