mass fractions of magnesium nitride

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magnesium nitride | elemental composition

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$Find the elemental composition for magnesium nitride in terms of the atom and mass percents: atom percent = N_i/N_atoms × 100% mass percent = (N_im_i)/m × 100% Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i, m_i, N_atoms and m using these items. • Finally, compute the percents and check the results. Write the chemical formula: Mg_3N_2 Use the chemical formula, Mg_3N_2, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms Mg (magnesium) | 3 N (nitrogen) | 2 N_atoms = 3 + 2 = 5 Divide each N_i by N_atoms to calculate atom fractions. Then use the property that atom fractions must sum to one to check the work: | number of atoms | atom fraction Mg (magnesium) | 3 | 3/5 N (nitrogen) | 2 | 2/5 Check: 3/5 + 2/5 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Mg (magnesium) | 3 | 3/5 × 100% = 60.0% N (nitrogen) | 2 | 2/5 × 100% = 40.0% Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table: | number of atoms | atom percent | atomic mass/u Mg (magnesium) | 3 | 60.0% | 24.305 N (nitrogen) | 2 | 40.0% | 14.007 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molecular mass, m: | number of atoms | atom percent | atomic mass/u | mass/u Mg (magnesium) | 3 | 60.0% | 24.305 | 3 × 24.305 = 72.915 N (nitrogen) | 2 | 40.0% | 14.007 | 2 × 14.007 = 28.014 m = 72.915 u + 28.014 u = 100.929 u Divide the mass for each element by m to calculate mass fractions. Then use the property that mass fractions must sum to one to check the work: | number of atoms | atom percent | mass fraction Mg (magnesium) | 3 | 60.0% | 72.915/100.929 N (nitrogen) | 2 | 40.0% | 28.014/100.929 Check: 72.915/100.929 + 28.014/100.929 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Mg (magnesium) | 3 | 60.0% | 72.915/100.929 × 100% = 72.24% N (nitrogen) | 2 | 40.0% | 28.014/100.929 × 100% = 27.76%$

Find the elemental composition for magnesium nitride in terms of the atom and mass percents: atom percent = N_i/N_atoms × 100% mass percent = (N_im_i)/m × 100% Plan: • Write the chemical formula and gather atomic masses from the periodic table. • Determine values for N_i, m_i, N_atoms and m using these items. • Finally, compute the percents and check the results. Write the chemical formula: Mg_3N_2 Use the chemical formula, Mg_3N_2, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms Mg (magnesium) | 3 N (nitrogen) | 2 N_atoms = 3 + 2 = 5 Divide each N_i by N_atoms to calculate atom fractions. Then use the property that atom fractions must sum to one to check the work: | number of atoms | atom fraction Mg (magnesium) | 3 | 3/5 N (nitrogen) | 2 | 2/5 Check: 3/5 + 2/5 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Mg (magnesium) | 3 | 3/5 × 100% = 60.0% N (nitrogen) | 2 | 2/5 × 100% = 40.0% Look up the atomic mass, m_i, in unified atomic mass units, u, for each element in the periodic table: | number of atoms | atom percent | atomic mass/u Mg (magnesium) | 3 | 60.0% | 24.305 N (nitrogen) | 2 | 40.0% | 14.007 Multiply N_i by m_i to compute the mass for each element. Then sum those values to compute the molecular mass, m: | number of atoms | atom percent | atomic mass/u | mass/u Mg (magnesium) | 3 | 60.0% | 24.305 | 3 × 24.305 = 72.915 N (nitrogen) | 2 | 40.0% | 14.007 | 2 × 14.007 = 28.014 m = 72.915 u + 28.014 u = 100.929 u Divide the mass for each element by m to calculate mass fractions. Then use the property that mass fractions must sum to one to check the work: | number of atoms | atom percent | mass fraction Mg (magnesium) | 3 | 60.0% | 72.915/100.929 N (nitrogen) | 2 | 40.0% | 28.014/100.929 Check: 72.915/100.929 + 28.014/100.929 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Mg (magnesium) | 3 | 60.0% | 72.915/100.929 × 100% = 72.24% N (nitrogen) | 2 | 40.0% | 28.014/100.929 × 100% = 27.76%