How many grams of KOH are required to prepare 500. mL of 0.450 KOH solution?

KOH  molar mass = 39 + 16 + 1 = 56g

To make 1 L of 1M soln needs 56g KOH

To make 500mL 1M needs 56/2 = 28g

To make 500mL 0.2M needs 28 x 0.2gn:

2h2o2--> 2h2o + o2

this reaction is of the spontaneous decomposition of hydrogen peroxide down into water and oxygen.

add 2 molecules of hydrogen peroxide and 2 molecules of water. since oxygen is naturally diatomic, the total number of atoms of each element is now the same on both sides of the equation so it is balanced.

this may not be entirely correct but let me know.