19.Give reasons: (a)-What will happen if a solution of sodium hydrogen carbonate(NaHCO3) is heated? (b)-Why should curd and sour substances not be kept in brass and copper vessels? (c)-Why does tooth decay start when pH of mouth is lower than 5.5? (d)- A mixture of oxygen and ethyne is burnt for welding. (e)-The element carbon forms a very large number of compounds.
Answers
a.) the following reaction takes place when it is heated during cooking- 2NaHCO₃→Na₂CO₃+H₂O+CO₂. Sodium carbonate is formed. b.) when curd and and sour substances are kept in brass and copper vessels they react with the elements forming respective salt and hydrogen . so we should not keep them in brass and copper vessels.Thus they may become poisonous. c.)Tooth decay starts when the pH of the mouth is lower than 5.5.Bacteria present in the mouth produce acids by degradation of sugars and food particles remaining in the mouth after eating.Tooth enamel , made up of calcium phosphate is the hardest substance in the body.It does not dissolve in water,but it is corroded when the pH in mouth is lower than 5.5. d.) When ethyne is burnt in air incomplete burning takes place and produce sooty flame due to limited supply oxygen present in the air. ... Hence, This oxy-acetylene flame is used for welding and it is not possible to attain such a high temperature with air. Due this reason a mixture of ethyne and air is not used for welding. e.)Carbon is the only element that can form so many different compounds because each carbon atom can form four chemical bonds to other atoms, and because the carbon atom is just the right, small size to fit in comfortably as parts of very large moleculestT