Element X has two isotopes. If 72.0% of the element has an isotope mass of 84.9 atomic mass units, and 28.0% of the element has an isotopic mass of 87.0 atomic mass units, the average atomic mass of element X is numerically equal to

Amonoprotic acid is an acid that donates a single proton to the solution. suppose you have 0.140 g of a monoprotic acid dissolved in 35.0 ml of water. this solution is then neutralized with 14.5 ml of 0.110 m naoh. what is the molar mass of the acid?

This graph gives information on changes in sea ice extent in the arctic ocean over a 30-year span. the overall trend shows in the ice extent. to address the trend, scientists need to ask themselves, one direct consequence of the trend is that

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.