The geometry of those electron groups might be tetrahedral, but not the geometry around the oxygen here, so the geometry around the oxygen, if you ignore the lone pairs of electrons, you can see that it is bent, so even though that oxygen is SP three hybridized, it's geometry is not tetrahedral; the geometry of that oxygen there is bent or angual. The CH 3 NH 3 + concentration is the same concentration as HCl. This is because the HCl (acid) that is added reacts with the CH 3 NH 2 (base). The moles of HCl that you add get neutralized by the base (since there are more moles of base in the beaker than acid added). In CH4, the molecular geometry is tetrahedral, so in C2H6 each C atom has a tetrahedral geometry. In CH3NH2, the arrangement around C is tetrahedral but around N, the arrangement is pyramidal. The -OH group in HCOOH has a bent arrangement as seen in water H-OH while the C atom has trigonal planar arrangement of H, O and OH.