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1. what is the mass number for a neon atom with 15 neutrons? what would…

Question

  1. what is the mass number for a neon atom with 15 neutrons? what would the atom’s full name be?
  2. what is the mass for copper - 75?
  3. how do you calculate average atomic mass?
  4. the element copper has naturally occurring isotopes with mass numbers 63 and 65. the masses are: 62.93 amu (69.2%) and 64.93 (30.8%). calculate the average atomic mass of copper. show all your work. use proper number of sig - figs throughout your work.
  5. rubidium is a soft, silvery - white metal that has two common isotopes, ⁸⁵rb and ⁸⁷rb. if the abundance of ⁸⁵rb is 72.2% and the abundance of ⁸⁷rb is 27.8%, what is the average atomic mass of rubidium?
  6. uranium is used in nuclear reactors and is a rare element on earth. uranium has three common isotopes. if the abundance of ²³⁴u is 0.01%, the abundance of ²³⁵u is 0.71%, and the abundance of ²³⁸u is 99.28%, what is the average atomic mass of uranium?

\ta. 69.2% for mass of 62.93amu
\tb. 30.8% for mass of 64.93amu.

  1. titanium has five common isotopes: ⁴⁶ti (8.0%), ⁴⁷ti (7.8%), ⁴⁸ti (73.4%), ⁴⁹ti (5.5%), ⁵⁰ti (5.3%). what is the average atomic mass of titanium?
  2. why is the mass in amu of a carbon - 12 atom reported as 12.011 in the periodic table of the elements?
  3. naturally occurring chlorine that is put in pools is 75.53 percent ³⁵cl (mass = 34.969 amu) and 24.47 percent ³⁷cl (mass = 36.966 amu). calculate the average atomic mass.
  4. copper used in electric wires comes in two flavors (isotopes): ⁶³cu and ⁶⁵cu. ⁶³cu has an atomic mass of 62.9298 amu and an abundance of 69.09%. the other isotope, ⁶⁵cu, has an abundance of 30.91%. the average atomic mass between these two isotopes is 63.546 amu. estimate the actual atomic mass of ⁶⁵cu.
  5. magnesium consists of three naturally occurring isotopes. the percent abundance of these isotopes is as follows: ²⁴mg (78.70%), ²⁵mg (10.13%), and ²⁶mg (11.7%). the average atomic mass of the three isotopes is 24.3050 amu. if the atomic mass of ²⁵mg is 24.98584 amu, and ²⁶mg is 25.98259 amu, estimate the actual atomic mass of ²⁴mg.

12.

Explanation:

Step1: Recall mass - number formula

The mass number ($A$) of an atom is the sum of the number of protons and neutrons. Neon has 10 protons. So for a neon atom with 15 neutrons, $A=10 + 15$.
$A = 25$
The full name of the atom is neon - 25.

Step2: Copper - 75 mass

The mass number of copper - 75 is approximately 75 amu. In reality, copper - 75 is not a stable isotope of copper, but if we consider the mass number convention, the mass is close to 75 amu.

Step3: Average atomic mass formula

The average atomic mass ($\bar{M}$) of an element with isotopes is calculated as $\bar{M}=\sum_{i = 1}^{n}M_i\times \%Ab_i$, where $M_i$ is the mass of the $i$-th isotope and $\%Ab_i$ is the percentage abundance of the $i$-th isotope (expressed as a decimal).

Step4: Calculate average atomic mass of copper

For copper with isotopes:
$M_1 = 62.93$ amu, $\%Ab_1=0.692$, $M_2 = 64.93$ amu, $\%Ab_2 = 0.308$
$\bar{M}=(62.93\times0.692)+(64.93\times0.308)$
$=(62.93\times0.692)=43.54756$
$(64.93\times0.308)=19.99844$
$\bar{M}=43.54756 + 19.99844=63.546\approx63.55$ amu

Step5: Calculate average atomic mass of rubidium

Let $M_1$ be the mass of $^{85}Rb$ and assume $M_1 = 85$ amu, $\%Ab_1 = 0.722$, $M_2$ be the mass of $^{87}Rb$ and assume $M_2 = 87$ amu, $\%Ab_2=0.278$
$\bar{M}=(85\times0.722)+(87\times0.278)$
$=(85\times0.722)=61.37$
$(87\times0.278)=24.186$
$\bar{M}=61.37+24.186 = 85.556\approx85.56$ amu

Step6: Calculate average atomic mass of uranium

Let $M_1$ be the mass of $^{234}U$ and assume $M_1 = 234$ amu, $\%Ab_1=0.0001$, $M_2$ be the mass of $^{235}U$ and assume $M_2 = 235$ amu, $\%Ab_2 = 0.0071$, $M_3$ be the mass of $^{238}U$ and assume $M_3 = 238$ amu, $\%Ab_3=0.9928$
$\bar{M}=(234\times0.0001)+(235\times0.0071)+(238\times0.9928)$
$=(234\times0.0001)=0.0234$
$(235\times0.0071)=1.6685$
$(238\times0.9928)=236.2864$
$\bar{M}=0.0234 + 1.6685+236.2864=237.9783\approx238.0$ amu

Step7: Calculate average atomic mass of titanium

Let $M_1 = 46$ amu, $\%Ab_1=0.08$, $M_2 = 47$ amu, $\%Ab_2=0.078$, $M_3 = 48$ amu, $\%Ab_3=0.734$, $M_4 = 49$ amu, $\%Ab_4=0.055$, $M_5 = 50$ amu, $\%Ab_5=0.053$
$\bar{M}=(46\times0.08)+(47\times0.078)+(48\times0.734)+(49\times0.055)+(50\times0.053)$
$=(46\times0.08)=3.68$
$(47\times0.078)=3.666$
$(48\times0.734)=35.232$
$(49\times0.055)=2.695$
$(50\times0.053)=2.65$
$\bar{M}=3.68+3.666 + 35.232+2.695+2.65=47.923\approx47.92$ amu

Step8: Carbon - 12 mass in periodic table

The mass of carbon - 12 reported as 12.011 amu in the periodic table is the average atomic mass of carbon. Carbon has isotopes like carbon - 12, carbon - 13 and a trace of carbon - 14. The average atomic mass takes into account the abundances of these isotopes.

Step9: Calculate average atomic mass of chlorine

Let $M_1 = 34.969$ amu, $\%Ab_1=0.7553$, $M_2 = 36.966$ amu, $\%Ab_2=0.2447$
$\bar{M}=(34.969\times0.7553)+(36.966\times0.2447)$
$=(34.969\times0.7553)=26.4221857$
$(36.966\times0.2447)=9.0456802$
$\bar{M}=26.4221857+9.0456802=35.4678659\approx35.47$ amu

Step10: Estimate atomic mass of $^{65}Cu$

Let the mass of $^{65}Cu$ be $x$ amu.
We know that $\bar{M}=63.546$ amu, $M_1 = 62.9298$ amu, $\%Ab_1=0.6909$, $\%Ab_2=0.3091$
$63.546=(62.9298\times0.6909)+(x\times0.3091)$
$(62.9298\times0.6909)=43.4882488$
$63.546 - 43.4882488=(x\times0.3091)$
$20.0577512=(x\times0.3091)$
$x=\frac{20.0577512}{0.3091}\approx64.89$ amu

Step11: Estimate atomic mass of $^{24}Mg$

Let the mass of $^{24}Mg$ be $y$ amu.
We know that $\bar{M}=24.3050$ amu, $M_2 = 24.98584$ amu, $\%Ab_2=0.1013$, $M_3 = 25.98259$ amu, $\%Ab_3=0.117$, $\%Ab_1=0.7870$
$24.3050=(y\time…

Answer:

  1. Mass number: 25, Atom's full name: neon - 25
  2. Approximately 75 amu
  3. $\bar{M}=\sum_{i = 1}^{n}M_i\times \%Ab_i$
  4. 63.55 amu
  5. 85.56 amu
  6. 238.0 amu
  7. 47.92 amu
  8. It is the average atomic mass considering carbon isotopes
  9. 35.47 amu
  10. 64.89 amu
  11. 23.80 amu