41) Answer is: the average atomic mass of chromium is 52.056.
Ar(⁵⁰Cr) = 50.
ω(⁵⁰Cr) = 4.34% ÷ 100%.
ω(⁵⁰Cr) = 0.0434; relative abundance of chromium-50.
Average mass can calculate by summary of percentege of each isotope.
Ar(Cr) = Ar(⁵⁰Cr) · ω(⁵⁰Cr) + Ar(⁵²Cr) · ω(⁵²Cr) + Ar(⁵³Cr) · ω(⁵³Cr) + Ar(⁵⁴Cr) · ω(⁵⁴Cr).
Ar(Cr)= 50 · 0.0434 + 52 · 0.8379 + 53 · 0.095 + 54 · 0.0237.
Ar(Cr) = 2.17 + 43.571 + 5.035 + 1.280
Ar(Cr) = 52.056.
42) Chlorine has atomic number 17, it means it has 17 protons and 17 electrons.
Electron configuration of chlorine atom: ₁₇Cl 1s² 2s² 2p⁶ 3s² 3p⁵.
Chloride is negative ion of chlorine. Chloride is formed when chlorine gain one lectron.
Chloride anion has 17 protons and 18 electrons (like argon-noble gas).
The electron configuration for the chloride ion: ₁₇Cl⁻ 1s²2s²2p⁶3s²3p⁶.
43) Anwser is: the percent by mass of hydrogen in aspirin is 4.48%.
% calculate by atomic mass of element multiply number of that element in molecule divided by molecular mass of molecule.
Ar(H) = 1.008; the relative atomic mass of hydrogen atom.
Mr(C₉H₈O₄) = 9 · Ar(C) + 8 · Ar(H) + 4 · Ar(O).
Mr(C₉H₈O₄) = 180.157.
ω(H)= 8 · Ar(H) ÷ Mr(C₉H₈O₄) · 100%.
ω(H) = 8 · 1.008 ÷ 180.157 · 100%.
ω(H) = 4.48 %.
44) Balanced chemical reaction:
Cd(NO₃)₂ + 2NH₄Cl → CdCl₂ + 2NH₄NO₃.
This chemical reaction is double displacement reaction - cations (Cd²⁺ and NH₄⁺) and anions (NO₃⁻ and Cl⁻) of the two reactants switch places and form two new compounds.
Cd(NO₃)₂ is cadmium nitrate.
NH₄Cl is amonium chloride.
CdCl₂ is cadmium chloride.
NH₄NO₃ is ammonium nitrate.