Which pairs of reactants will result in a chemical reaction? Cr(s) + AgClO
(aq) Pt(s) + CoBr
(aq) Zn(s) + CuNO
(aq) Ni(s) + MgCl
(aq)
The Correct Answer and Explanation is:
Activity Series Overview (in simplified order from most to least active):
K > Ca > Na > Mg > Al > Zn > Cr > Fe > Ni > Sn > Pb > H > Cu > Hg > Ag > Pt > Au
Step-by-step Analysis:
- Pt(s) + CoBr₂(aq)
Cobalt (Co) is higher than platinum (Pt) on the activity series. Therefore, Pt is less reactive and cannot displace Co from CoBr₂.
No reaction. - Zn(s) + CuNO₃(aq)
Zinc (Zn) is higher than copper (Cu) on the activity series. Therefore, Zn can displace Cu from CuNO₃, forming Zn(NO₃)₂ and Cu(s).
Reaction occurs. - Ni(s) + MgCl₂(aq)
Magnesium (Mg) is higher than nickel (Ni). Thus, Ni cannot displace Mg from MgCl₂.
No reaction. - Cr(s) + AgClO₄(aq)
Chromium (Cr) is much higher than silver (Ag) in the activity series. Cr can displace Ag from AgClO₄, forming Cr(ClO₄)₃ and Ag(s).
Reaction occurs.
Final Answer:
Reactions occur for:
- Zn(s) + CuNO₃(aq)
- Cr(s) + AgClO₄(aq)
Textbook-Style Explanation
In single replacement reactions, a free metal reacts with a compound containing a metal cation. Whether a reaction occurs depends on the activity series, which ranks metals by their tendency to lose electrons and form cations. A more active metal can displace a less active metal from a compound in aqueous solution. This principle allows us to predict the outcome of each reaction.
Consider the first pair: Pt(s) + CoBr₂(aq). Platinum is one of the least reactive metals, found near the bottom of the activity series. Cobalt is higher, meaning it is more reactive. Since platinum is less reactive, it cannot displace cobalt from the solution. Therefore, no reaction occurs.
The second reaction: Zn(s) + CuNO₃(aq) involves zinc, which is more reactive than copper. Zinc can displace copper from its nitrate salt, forming Zn(NO₃)₂ in solution and precipitating metallic copper. This is a classic single replacement reaction.
In the third pair: Ni(s) + MgCl₂(aq), nickel is lower than magnesium on the activity series. Because nickel is less reactive, it cannot displace magnesium. Thus, no reaction takes place.
Finally, Cr(s) + AgClO₄(aq) involves chromium, which is far more reactive than silver. Chromium displaces silver from silver perchlorate, forming Cr(ClO₄)₃ and solid silver. This is a successful single replacement reaction.
In conclusion, a chemical reaction will only occur if the solid metal is more reactive than the metal in the aqueous compound. Based on the activity series, only Zn with CuNO₃ and Cr with AgClO₄ result in observable chemical reactions.
