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Electrolysis of brine turns NaCl and water into NaOH, H2 and Cl2. Which balanced molecular equation is correct?
ANaCl + H2O gives NaOH + H2 + Cl2
B2NaCl + H2O gives 2NaOH + H2 + Cl2
C2NaCl + 2H2O gives 2NaOH + H2 + Cl2
D2NaCl + 2H2O gives NaOH + 2H2 + Cl2
Answer & Solution
Correct answer: C. 2NaCl + 2H2O gives 2NaOH + H2 + Cl2
1. Chlorine leaves as Cl2, so at least 2 Cl atoms are needed, which fixes NaCl at 2.
2. Those 2 Na atoms must end up in 2 NaOH.
3. The 2 OH groups need 2 O atoms, so 2 H2O are required on the left.
4. Count hydrogen: 2 H2O supply 4 H atoms, and 2 NaOH use 2 of them.
5. The remaining 2 H atoms form 1 H2, so the equation is 2NaCl + 2H2O giving 2NaOH + H2 + Cl2.
6. Option B leaves oxygen short, since 1 H2O cannot supply 2 OH groups.
7. Option D leaves sodium unbalanced at 2 against 1.
_Source: OpenStax Chemistry (CC BY 4.0), Ch 4 "Stoichiometry of Chemical Reactions", section 4.1 Writing and Balancing Chemical Equations_
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