Question #94b00

1 Answer
May 1, 2017

Answer:

The expected mass is 23.184 016 u.

Explanation:

A nucleus of #""_11^23"Na"# contains 11 protons and 12 neutrons.

Its expected mass is the sum of the masses of its protons and neutrons.

Here's how to calculate the expected mass:

#"Mass of protons":color(white)(mll) "11 × 1.007 276 u" = "11.080 036 u"#
#"Mass of neutrons": color(white)(m)"12 × 1.008 665 u" = "12.103 980 u"#
#color(white)(mmmmmmmmmmmml)"Total mass/u":color(white)(l)stackrel(—————)("23.184 016 u")#

∴ The expected mass is 23.184 016 u.

Note: This is different from the actual mass of a nucleus of #""_11^23"Na"#, which is 22.989 769 u.

The difference in mass is called the mass defect.