Question

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Answer 1

A) i) In plaster of Paris two formula units of CaSO4 share one molecule of water. In the formula it is written as half water molecule because in the formula we are showing only one unit of CaSO4.
ii) when hydrate is heated water molecules face a choice.when all the water is evaporated from hydrate copper ions are left with only sulfate ions in their surroundings. As a result substance changes its colour from blue to white .
B) i) when the pH in the mouth falls below 5.5 it can cause tooth decay . The basic compound of tooth enamel ( i.e calcium phosphate) is attacked by acids .we can prevent it by neutralising.
ii) The acidic behaviour of acid is due to the presence of hydrogen ions. The acids will not show its acidic behaviour in the absence of water this is because the acids produce hydrogen ions only in the presence of water.