Q. Balance a chemical equation of Fe + H2O ———–> Fe3O4 + H2 with steps.
Step 1: Balance atoms of elements present in the highest number in the reaction.
e.g. Fe + 4H2O -----------> Fe3O4 + H2
Step 2: Balance other elements.
3Fe + 4H2O ———–> Fe3O4 + 4H2
Step 3: Check if the equation is balanced. (If not write the value in the factorial form and multiply all number with its denominator)
Step 4: Add the state of the elements and compound formed and conditions. e.g. Solid(s), Liquid(l), Gas(g), Sunlight, Heat
3Fe(s) + 4H2O(l) ———–> Fe3O4(s) + 4H2(g)
Q. Write a short note on the types of chemical reaction with an example.
a. Combination reaction:
CaO(s) + H2O(l) ----------> Ca(OH)2(aq)
Carbon(s) + O2(g) ----------> C02(g)
b. Decomposition reaction
CaCO3(s) ---------------> CaO + CO2(g)
Limestone Quick lime
c. Displacement reactions:
Iron displaces Copper from Copper sulphate solution(Blue) to form colourless Ferrous sulphate.
Fe(s) + CuSO4(aq) -----------> FeS04(aq) + Cu(s)
d. Double displacement reaction
Take a salt with another salt or a acid with base
2NaS04(aq) + 2BaCl2(aq) --------------> 2BaS04(s) + 2NaCl(aq)
e. Oxidation- reduction reaction
Oxidation: Copper on heating combines with oxygen to form its oxide(Black).
2Cu(s) + O2 ----------> 2CuO(s)
Reduction: Copper oxide on heating in presence of hydrogen gas yields pure copper
Q. What is corrosion.
Hint: Rusting of iron, Blackening of silver, copper.
Q. What is rancidity? How is it prevented?
Hint: Oxidation of fats and oils.
Prevented by use of anti-oxidant, nitrogen gas
Q. Give an example of precipitation reaction.
Hint: Silver nitrate with NaCl, Barium chloride with sodium sulphate.