Question

PLEASE HELP ASAP!!!

There are four isotopes of lead and their relative abundance listed below.  Use this information to calculate the approximate atomic mass of lead.  Show all work clearly!!  (4 points)

           82 protons, 122 neutrons, 1.4%

           82 protons, 125 neutrons, 22.1%

          82 protons, 124 neutrons, 24.1%

         82 protons, 126 neutrons, 52.4%

PLEASE SHOW WORK!!!

Answer 1

207.2 g/mol

Step-by-step 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

Answer 2

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}* {{\text {fractional abundance}}`

Average atomic mass of given element =
`(204* 0.014+207* 0.221 +206* 0.241+208* 0.524)=207.24`

The approximate atomic mass of lead is 207.24.