Catalyst:
A catalyst is a substance which increase the rate of chemical reaction. Catalyst reduce the time taken to reach equilibrium, but they have no effect on the position of equilibrium once this is reached.
how sulphuric acid can be diluted taste:
The addition of water to the concentrated sulphuric acid produces a vigorous reaction, which often causes acid droplets to spew in all directions. For this reason this must be avoided. Always add the acid to water when diluting it.