Multiple Choice
In which of the following reactions does the oxidation number of oxygen increase?
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6. Chemical Quantities & Aqueous Reactions
Calculate Oxidation Numbers
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In which reaction does the oxidation number of oxygen increase (i.e., becomes less negative or more positive)?
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Verified step by step guidance1
Identify the oxidation number of oxygen in each reactant and product for all given reactions. Remember, oxygen usually has an oxidation number of -2 in most compounds, except in peroxides or when bonded to fluorine.
For the first reaction: \$2H_2O_2 \rightarrow 2H_2O + O_2\(, determine the oxidation number of oxygen in hydrogen peroxide (\)H_2O_2\(), water (\)H_2O\(), and molecular oxygen (\)O_2$).
Recall that in \(H_2O_2\), oxygen has an oxidation number of -1 (since it is a peroxide), in \(H_2O\) it is -2, and in \(O_2\) (elemental form) it is 0. Compare these values to see if oxygen's oxidation number increases (becomes less negative or more positive).
Repeat the oxidation number analysis for the second reaction: \(C_3H_8 + 5O_2 \rightarrow 3CO_2 + 4H_2O\). Oxygen in \(O_2\) is 0, in \(CO_2\) it is -2, and in \(H_2O\) it is -2. Check if oxygen's oxidation number increases in any product compared to reactants.
For the third reaction: \$2Mg + O_2 \rightarrow 2MgO\(, oxygen goes from 0 in \)O_2\( to -2 in \)MgO$. Determine if this is an increase or decrease in oxidation number. Based on these comparisons, identify which reaction shows an increase in oxygen's oxidation number.
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