Question

PLEASE HELP ASAP!!!

Answer 1

Answer: 207.24

Explanation: Atomic mass = no of protons + no of neutrons

1) 82 protons, 122 neutrons , mass number= 82+122 = 204

2) 82 protons, 125 neutrons,  mass number= 82+125 = 207

3) 82 protons, 124 neutrons, mass number= 82+124 = 206

4) 82 protons, 126 neutrons, mass number= 82+126 = 208

Average atomic mass of an element =  $\sum(\text{atomic mass of an isotopes}\times {{\text {fractional abundance}}$

Average atomic mass of given element =  $(204\times 0.014+207\times 0.221 +206\times 0.241+208\times 0.524)=207.24$

The approximate atomic mass of lead is 207.24.

Answer 2

Answer:

207.2 g/mol

Explanation:

To answer this question you must know the atomic mass of one proton and one neutron are both 1 g/mol. Thus, mass of each isotope is:

²⁰⁴Pb: 82×1g/mol + 122×1g/mol = 204 g/mol

²⁰⁷Pb: 82×1g/mol + 125×1g/mol = 207 g/mol

²⁰⁶Pb: 82×1g/mol + 124×1g/mol = 206 g/mol

²⁰⁸Pb: 82×1g/mol + 126×1g/mol = 208 g/mol

Atomic mass is the pondered average of mass of isotopes. Thus, atomic mass of lead is:

204 g/mol × 0.014 + 207 g/mol × 0.221 + 206 g/mol × 0.241 + 208 g/mol × 0.524 =

207.2 g/mol