[kenny1999]

how to compare relative strength of reducing agent.
for example, given two chemical substances.
aqueous ammonia and zinc granule.

i know that ammonia can be reducing agent sometimes (for example when it meets oxygen or fluorine, is it? ) ..and zinc granule can be a reducing agent if it meets solutions of metal ions of lower reactivity e.g. iron(ii) or iron(iii) sulphate etc

but how can i know which one (aq ammonia or zinc) is a stronger reducing agent in a qualitative way ? (That means WITHOUT understanding reduction potential because it is out of syllabus and more importantly, somebody (reliable) says it is possible to know without the concept of reduction potential)

hope someone would help thanks!!

[Fzang]

Electropositive compounds will more easily donate their electron (i.e. reduce)
Electronegative compounds will more easily accept an electron (i.e. oxidize)

Electronegativity increases as you go right and up in the periodic table. (So O and F are very strong oxidizing agents)
Electropositivity increases as you go left and down in the periodic table. (Li and Na are thus very strong reducing agents)

When an acid donates a proton, H⁺, this proton is reduced to H₂(g), meaning the other compound is oxidized, because it has lost electrons to the proton.

NH₄⁺ is an acid and N is fully reduced, so this is probably a better oxidizing agent than Zn which is usually converted to Zn²⁺, thus being a reducing agent.

[kenny1999]

Electropositive compounds will more easily donate their electron (i.e. reduce)
Electronegative compounds will more easily accept an electron (i.e. oxidize)

Electronegativity increases as you go right and up in the periodic table. (So O and F are very strong oxidizing agents)
Electropositivity increases as you go left and down in the periodic table. (Li and Na are thus very strong reducing agents)

When an acid donates a proton, H⁺, this proton is reduced to H₂(g), meaning the other compound is oxidized, because it has lost electrons to the proton.

NH₄⁺ is an acid and N is fully reduced, so this is probably a better oxidizing agent than Zn which is usually converted to Zn²⁺, thus being a reducing agent.

thanks but what is the equation of aq ammonia being a reducing agent? how NH4+ loses/provide electrons as a reducing agent? All outermost shell electrons of NH4+ is already bonded with hydrogen atoms.. i don't think those electrons will lose.

[Fzang]

NH₃ + 2 O₂ → HNO₃ + H₂O

N is oxidized from -3 to +5, while oxygen is reduced from 0 to -2.