Acid-base background

Every anion in the scheme is the base of an acid-base conjugate pair such as the six shown in the table below.  Consideration of that table shows 

• if one member of a conjugate pair is strong, the other member does not react with water.
  
  Thus anions that have strong conjugate acids are NOT basic.
  The common monoprotic strong acids  are HCl, HBr, HI, HNO₃, H₂SO₄ (HSO₄^- moderately strong).  You will already know these.  HIO₃ is also strong.
  
   
• both members of weak acid-base conjugate pairs react with water to change its pH.
  
  Thus anions that have weak conjugate acids are basic.
  Most monoprotic acids other than those mentioned above are weak.
  
  

  pH = –log[H3O+]	aqueous solution has no effect on litmus		aqueous solution turns blue litmus red and has a lower pH than H2O
  acid	CH3OH not acidic	H2O	NH4+ weak acid	weak acid	H3O+	HCl strong acid
  conjugate base	CH3O– strong base	OH–	NH3 weak base	weak base	H2O	Cl– not basic
  	aqueous solution turns red litmus blue and has a higher pH than H2O				aqueous solution no effect on litmus