Spectrophotometer measures the transmittance or the absorbance, or both, of a particular wavelength or light after it has passed through a liquid sample. the liquid sample holder is commonly known as a cuvette. before the transmittance or absorbance of the sample is measured, a cuvette filled only with solvent, called the blank, is placed in the spectrophotometer. select the statement from the following that is true for why is a blank measured before the sample.
a. a blank is measured to remove the signal caused by the cuvette walls and solvent.
b. a blank is measured to calibrate the spectrophotometer's light source.
c. there is no reason to measure a blank before the sample.
d. a blank is measured to clean the spectrophotometer.

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.

What is the value of keq for the reaction expressed in scientific notation?

When water dissociates, each water molecule splits into a hydroxide ion and a) h 3 o + b) a hydrogen atom c) a hydrogen ion d) h 2 o e) oh —