Specific Charge!!

Firstly,



shows an atomic mass of 24 (neutrons + protons)
shows proton number 12

Secondly, it is a magnesium ion (charge +2)

Thirdly, the book uses really accurate values of 1/avogadro and elementary charge in addition to crazy rounding.



So using:

$S.C = charge/mass$

$Charge = 2\times 1.60 \times 10^{-19}[br]\\\\=3.2\times 10^{-19}$

$Mass = 24\times 6.02 \times 10^{-27}$

$S.C = 8.036\times 10^6 Ckg^{-1}$ or $8.04\times 10^6 Ckg^{-1}$ to 1dp

]
how would you calculate $Cu_{29}^{63}$ when it loses two electrons?
Are there any rules which makes this easier? Is there a different method for calculating the SC of an ion to a charged particle?

So using:

$S.C = charge/mass$

$Charge = 2\times 1.60 \times 10^{-19}[br]\\\\=3.2\times 10^{-19}$

$Mass = 24\times 1.67 \times 10^{-27}$ Sorry, typo before.

$S.C = 8.036\times 10^6 Ckg^{-1}$ or $8.04\times 10^6 Ckg^{-1}$ to 1dp

I don't get it at all. Some answers seem to be correct and others don't, even with the same working out.
Q) An isotope of Uranium has 92 protons and 143 neutrons. Calculate its specific charge in $Ckg^{-1}$
$C=\frac{92 \times 1.6 \times 10^{-19}}{235 \times 1.67 \times 10^{-27}}$
$C=3.8 \times10^7Ckg^{-1}$
Ok so that's correct.
However, if I apply the exact same working $S.C.=\frac{charge}{mass}$ it's not correct. For example,
Q) $Mg_{12}^{24}$
charge = $24 \times 1.60 \times 10^{-19}=3.84 \times 10^{-18}$
mass = $24 \times 1.67 \times 10^{-27}=4 \times 10^{-26}$
S.C.=$\frac{3.84 \times 10^{-18}}{4 \times 10^{-26}}=9.6 \times 10^6Ckg^{-1}$
This is wrong. The book states the s.c. is $8.04 \times10^6Ckg^{-1}$
It also states the charge is $3.2 \times 10^{-19}$ not $3.84 \times 10^{-18}$. Why is this?
To calculate the charge (not specific charge) of a particle, I am multiplying the proton number by $1.6 \times 10^{-19}$, since neutrons have no charge.
To calculate the mass, I am multiplying the nucleon number (protons and neutrons) by $1.67 \times 10^{-27}$ yet this isn't correct.
What am I doing wrong here?