mass fractions of hydrazine monohydrochloride

hydrazine monohydrochloride | elemental composition

Find the elemental composition for hydrazine monohydrochloride 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: NH_2NH_2·HCl Use the chemical formula, NH_2NH_2·HCl, to count the number of atoms, N_i, for each element and find the total number of atoms, N_atoms: | number of atoms Cl (chlorine) | 1 H (hydrogen) | 5 N (nitrogen) | 2 N_atoms = 1 + 5 + 2 = 8 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 Cl (chlorine) | 1 | 1/8 H (hydrogen) | 5 | 5/8 N (nitrogen) | 2 | 2/8 Check: 1/8 + 5/8 + 2/8 = 1 Compute atom percents using the atom fractions: | number of atoms | atom percent Cl (chlorine) | 1 | 1/8 × 100% = 12.5% H (hydrogen) | 5 | 5/8 × 100% = 62.5% N (nitrogen) | 2 | 2/8 × 100% = 25.0% 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 Cl (chlorine) | 1 | 12.5% | 35.45 H (hydrogen) | 5 | 62.5% | 1.008 N (nitrogen) | 2 | 25.0% | 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 Cl (chlorine) | 1 | 12.5% | 35.45 | 1 × 35.45 = 35.45 H (hydrogen) | 5 | 62.5% | 1.008 | 5 × 1.008 = 5.040 N (nitrogen) | 2 | 25.0% | 14.007 | 2 × 14.007 = 28.014 m = 35.45 u + 5.040 u + 28.014 u = 68.504 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 Cl (chlorine) | 1 | 12.5% | 35.45/68.504 H (hydrogen) | 5 | 62.5% | 5.040/68.504 N (nitrogen) | 2 | 25.0% | 28.014/68.504 Check: 35.45/68.504 + 5.040/68.504 + 28.014/68.504 = 1 Compute mass percents using the mass fractions: Answer: | | | number of atoms | atom percent | mass percent Cl (chlorine) | 1 | 12.5% | 35.45/68.504 × 100% = 51.75% H (hydrogen) | 5 | 62.5% | 5.040/68.504 × 100% = 7.357% N (nitrogen) | 2 | 25.0% | 28.014/68.504 × 100% = 40.89%

Mass fraction pie chart