A metal in its elemental form displaces another metal from its compound. The displacing metal must be a stronger reducing agent (more capable of losing electrons) than the metal being displaced.
Examples:
C u + 2 S + 6 O 4 − 2 ( a q ) + Z n 0 ( s ) → C u 0 ( s ) + Z n + 2 S + 6 O 4 − 2 ( a q ) ( 7.29 ) \overset{+2}{Cu}\overset{+6}{S}\overset{-2}{O_4}(aq) + \overset{0}{Zn}(s) \rightarrow \overset{0}{Cu}(s) + \overset{+2}{Zn}\overset{+6}{S}\overset{-2}{O_4}(aq) \qquad(7.29) C u + 2 S + 6 O 4 − 2 ( a q ) + Z n 0 ( s ) → C u 0 ( s ) + Z n + 2 S + 6 O 4 − 2 ( a q ) ( 7.29 )
Zinc is oxidised (0 → +2), copper is reduced (+2 → 0).
V 2 + 5 O 5 − 2 ( s ) + 5 C a 0 ( s ) → Δ 2 V 0 ( s ) + 5 C a + 2 O − 2 ( s ) ( 7.30 ) \overset{+5}{V_2}\overset{-2}{O_5}(s) + 5\overset{0}{Ca}(s) \xrightarrow{\Delta} 2\overset{0}{V}(s) + 5\overset{+2}{Ca}\overset{-2}{O}(s) \qquad(7.30) V 2 + 5 O 5 − 2 ( s ) + 5 C a 0 ( s ) Δ 2 V 0 ( s ) + 5 C a + 2 O − 2 ( s ) ( 7.30 )
Calcium is oxidised (0 → +2), vanadium is reduced (+5 → 0).
T i + 4 C l 4 − 1 ( l ) + 2 M g 0 ( s ) → Δ T i 0 ( s ) + 2 M g + 2 C l 2 − 1 ( s ) ( 7.31 ) \overset{+4}{Ti}\overset{-1}{Cl_4}(l) + 2\overset{0}{Mg}(s) \xrightarrow{\Delta} \overset{0}{Ti}(s) + 2\overset{+2}{Mg}\overset{-1}{Cl_2}(s) \qquad(7.31) T i + 4 C l 4 − 1 ( l ) + 2 M g 0 ( s ) Δ T i 0 ( s ) + 2 M g + 2 C l 2 − 1 ( s ) ( 7.31 )
Magnesium is oxidised (0 → +2), titanium is reduced (+4 → 0).
C r 2 + 3 O 3 − 2 ( s ) + 2 A l 0 ( s ) → Δ A l 2 + 3 O 3 − 2 ( s ) + 2 C r 0 ( s ) ( 7.32 ) \overset{+3}{Cr_2}\overset{-2}{O_3}(s) + 2\overset{0}{Al}(s) \xrightarrow{\Delta} \overset{+3}{Al_2}\overset{-2}{O_3}(s) + 2\overset{0}{Cr}(s) \qquad(7.32) C r 2 + 3 O 3 − 2 ( s ) + 2 A l 0 ( s ) Δ A l 2 + 3 O 3 − 2 ( s ) + 2 C r 0 ( s ) ( 7.32 )
Aluminium is oxidised (0 → +3), chromium is reduced (+3 → 0). …