Copper has two naturally occurring isotopes, 63 cu and 65 cu. if that is the case, why is the atomic mass of the copper listed as 63.55 amu on the periodic table

Explanation: There are 2 given isotopes of Copper.

Mass number of Isotope 1 : 63amu

Mass number of Isotope 2: 65 amu

Let the fractional abundance of isotope 1 be 'x', so the fractional abundance for Isotope 2 will be '1-x'

The average atomic number of Copper given is 63.55 amu.

So, the formula for average atomic mass is given by:

Putting values in above equation, we get:

The fractional abundance of Isotope 1 = 0.725

The fractional abundance of Isotope 2 = 0.275

So, the natural percentage abundance for isotope 1 = 72.5%

The natural percentage abundance for isotope 2 = 27.5%

Whenever more number of isotopes are present of an element are present, we take the average atomic mass of that element.

the grams   of   barium that   are in   2.3 x 10^23   atoms of barium   is   52.4 g (answer c)

    calculation

mass = moles   of ba   x molar   mass of ba

  molar mass of ba from periodic table=   137.3 g/mol

  use the   avogadro's law   constant   to   calculate the moles of barium

  that   is     1 mole =   6.02   x 10^23 atoms

                    ? moles = 2.3 x 10^23   atoms

by cross   multiplication

=(1 mole   x 2.3x 10^23 atoms)   / 6.02   x10^23 atoms)=   0.382   moles

mass   is therefore = 137.3   g/mol x 0.382 mol = 52.4 ( answer c)

explanation:

the answer is 1260

you spend 7 hours in school for 1 school day with 5 school days in 1 school week with 36 school weeks in a school year.

7*5*36= 1260 it's all about multiplying