 5 is a powerful Lewis acid used to make the superacid fluoroantimonic acid ( " H2SbF7 " ) . 
 5 <a href='drop_aux' title='1'><mark>is</mark></a>a powerful Lewis acid used to make the superacid fluoroantimonic acid ( " H2SbF7 " ) . 
5 a powerful Lewis acid used to make the superacid fluoroantimonic acid ( " H2SbF7 " ) .