A solution is made by dissolving 0.40 g of solid sodium hydroxide in 250cm of water. It is found that 28.2 cm of this solution is needed to completely neutralise a 40.0cm sample of ethanoic acid (CH3COOH) of unknown
concentration.
Calculate the concentration of ethanoic acid.

What is the h+ concentration for an aqueous solution with poh = 4.01 at 25 ∘c? express your answer to two significant figures and include the appropriate units.

Determine the wavelength of the light absorbed when an electron in a hydrogen atom makes a transition from an orbital in the n=3 level to an orbital in the n=7 level.

Two nitro no2 groups are chemically bonded to a patch of surface. they can't move to another location on the surface, but they can rotate (see sketch at right). it turns out that the amount of rotational kinetic energy each no2 group can have is required to be a multiple of ε, where =ε×1.010−24 j. in other words, each no2 group could have ε of rotational kinetic energy, or 2ε, or 3ε, and so forth — but it cannot have just any old amount of rotational kinetic energy. suppose the total rotational kinetic energy in this system is initially known to be 32ε. then, some heat is removed from the system, and the total rotational kinetic energy falls to 18ε. calculate the change in entropy. round your answer to 3 significant digits, and be sure it has the correct unit symbol.