The nuclide as-76 has a half-life of 26.0 hours. if a sample of as-76 weighs 344 g, what mass of as-76 remains after 538 minutes?

The amount of substance after t hours with the given half-life can be calculated through the equation,

                     A(t)  = A(o) x (0.5)^(t/h)

where A(t) is the amount after t hours, A(o) is the original amount, h is the half-life.

Substituting the known values from the given,

It must be noted that the number of minutes should be converted first to hours by dividing it by 60. 

                  A(t) = (344 g) x (0.5)^((538/60)/26))
                       A(t) = 270.86 g
Thus, the amount of as-76 after 538 minutes is approximately 270.86 g.