Question

atomic mass practice

1. which isotope of copper is more abundant: copper - 63 or copper - 65? (the atomic mass of copper is 63.546 amu)
2. element x has two natural isotopes. the isotope with a mass of 10.012 amu (¹⁰x) has a relative abundance of 19.91%. the isotope with a mass of 11.009 amu (¹¹x) has a relative abundance of 80.09%. calculate the atomic mass of this element.
3. calculate the atomic mass of bromine. the two isotopes of bromine have atomic masses and relat abundance of 78.92 amu (50.69%) and 80.92 amu (49.31%).

Explanation:

Step1: Formula for atomic mass

The formula for atomic mass \( M\) of an element with two isotopes is \( M = m_1\times a_1 + m_2\times a_2\), where \( m_1\) and \( m_2\) are the masses of the isotopes, and \( a_1\) and \( a_2\) are their relative abundances (expressed as decimals).

Step2: Convert abundances to decimals

For element \( X\), \( a_1=0.1991\) (since \( 19.91\%=\frac{19.91}{100} = 0.1991\)) and \( a_2 = 0.8009\) (since \( 80.09\%=\frac{80.09}{100}=0.8009\)), \( m_1 = 10.012\) amu, \( m_2=11.009\) amu.
Substitute into the formula:

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Answer:

The atomic mass of element \( X\) is approximately \( 10.81\) amu.