Which pairs of reactants will result in a chemical reaction?
- Mn(s) + AgClO3(aq)
- Hg(s) + CoBr2(aq)
- Ni(s) + MgCl2(aq)
- Cd(s) + CuNO3(aq)
The Correct Answer and Explanation is:
To determine which pairs of reactants will result in a chemical reaction, we need to apply the concept of single-replacement reactions and the activity series of metals.
A single-replacement reaction occurs when a more reactive metal displaces a less reactive metal from its compound (usually in aqueous solution). The general form is:
A (metal) + B⁺X⁻ (metal salt) → A⁺X⁻ + B (solid metal)
This reaction only proceeds if metal A is more reactive than metal B, which is determined using the activity series of metals.
Here is the list of the metals involved and their positions (from most to least reactive):
- Mn (Manganese) – very reactive
- Cd (Cadmium) – moderately reactive
- Ni (Nickel) – less reactive than Mn and Cd
- Hg (Mercury) – low reactivity
- Mg (Magnesium) – very reactive
- Cu (Copper) – low reactivity
- Co (Cobalt) – reactive
- Ag (Silver) – very low reactivity
Now, let’s analyze each pair:
- Mn(s) + AgClO₃(aq)
Mn is more reactive than Ag.
✅ Reaction occurs: Mn displaces Ag from AgClO₃. - Hg(s) + CoBr₂(aq)
Hg is less reactive than Co.
❌ No reaction: Hg cannot displace Co. - Ni(s) + MgCl₂(aq)
Ni is less reactive than Mg.
❌ No reaction: Ni cannot displace Mg. - Cd(s) + CuNO₃(aq)
Cd is more reactive than Cu.
✅ Reaction occurs: Cd displaces Cu from CuNO₃.
✅ Correct pairs that will result in a reaction:
- Mn(s) + AgClO₃(aq)
- Cd(s) + CuNO₃(aq)
These reactions occur because manganese and cadmium are higher on the activity series than silver and copper, respectively. They can lose electrons more easily and thus replace the less reactive metals in their ionic compounds, forming new compounds and releasing the replaced metal as a solid.
