7.44. General chemical properties of metals

General chemical properties of metals

In terms of chemical properties, metals are reducing agents, since they readily give up their electrons to nonmetal atoms, turning into positively charged ions — cations.

The ability of metal atoms to give up electrons, and of their cations to accept electrons, can serve as a measure of their chemical activity. Thus, aluminum becomes covered with an oxide film very quickly in air, while no noticeable changes occur with gold. Zinc reacts actively with hydrochloric acid, while silver does not. Therefore, aluminum and zinc can be classified as active metals, while gold and silver are inactive.

The activity series of metals

The chemical activity of different metals is easy to compare by analyzing their behavior in aqueous solutions of salts and acids. For example, if a zinc plate or an iron nail is placed in a solution of copper(II) sulfate, a reddish coating of copper appears on its surface almost immediately. This shows that zinc and iron displace copper from the solution. These processes can be represented by the following equations:

Zn + CuSО4 = ZnSО4 + Сu↓,

Zn0 + Сu2+ = Zn2+ + Cu0;

Fe + CuSО4 = FeSО4 + Сu↓,

Fe0 + Cu2+ = Fe2+ + Сu0.

In these reactions, zinc and iron give up their electrons to copper ions, that is, they are oxidized. Copper ions accept electrons, so copper is reduced.

If instead a copper plate is placed in a solution of zinc sulfate, no deposition of zinc occurs on it. What is the reason for this?

By experimentally studying the ability of some metals to displace others from aqueous solutions of their salts, the Russian scientist N. N. Beketov arranged the metals in a series. In it, the metals located further to the left are able to reduce the subsequent ones from solutions of their salts. Since this ability of metals is related to their reducing activity, this series is called the activity series of metals.

Activity series of metals

Li K Ba Sr Cа Na Mg Al Mn Zn Cr Fe Ni Sn Pb (H2) Cu Hg Ag Pd Pt Au

The further to the left a metal is located in this series, the greater its reducing properties in an aqueous solution, that is, the more easily it gives up its electrons to an oxidizing agent and passes into solution as a cation; and the harder it is for a cation of this metal to be reduced. Zinc and iron give up their electrons more easily than copper, and therefore they reduce Cu2+ from solution.

Based on the position of zinc in the activity series, it can be predicted that this metal is able to reduce tin, copper, and silver ions from solution:

Zn0 + Sn2+ = Zn2+ + Sn0;

Zn0 + Сu2+ = Zn2+ + Cu0;

Zn0 + 2Ag+ = Zn2+ + 2Ag0.

At the same time, copper will reduce only silver ions, but will not reduce tin ions:

Cu0 + 2Ag+ = Cu2+ + 2Ag0.

This means that zinc has a greater reducing ability. It gives up electrons more easily than tin, copper, and silver. Therefore, zinc is considered a more active metal than these metals. In turn, copper is a more active metal than silver.

The activity series of metals allows one not only to predict the behavior of metals in reactions with salt solutions, but also to compare their relationship to water, acid solutions, and also to nonmetals and a number of other substances.

Thus, to the left of hydrogen are located the metals that displace hydrogen from water and acids (that is, reduce hydrogen ions Н+). Metals located to the right of hydrogen do not exhibit such reducing activity in reactions with acid solutions. For example, zinc reacts with hydrochloric acid, displacing hydrogen:

Zn + 2НСl = ZnCl2 + Н2↑,

Zn0 + 2Н+ = Zn2+ + ,

while silver does not displace hydrogen.

The diagram shows the dependence of the chemical activity of metals on their position in the activity series and their interaction with various substances.

1. Interaction with oxygen

Metals react with oxygen:

• active metals are oxidized in air
• less active ones — upon heating
• noble metals — do not react

2. Interaction with water

Reaction of metals with water:

• very active metals form a hydroxide and release hydrogen
• metals of medium activity react only upon heating
• low-activity metals do not react

3. Activity series of metals

From more active to less active:

Li → K → Ca → Na → Mg → Al → Mn → Zn → Fe → Ni → Sn → Pb → (H₂) → Cu → Hg → Ag → Pt → Au

Moving from left to right:

• the ability of atoms to give up electrons decreases
• reducing properties decrease

4. Interaction with hydrochloric acid

Metals standing before hydrogen in the activity series react with hydrochloric acid:

• hydrogen is released
• a salt is formed

Metals after hydrogen — do not react

5. Interaction with sulfuric acid

With sulfuric acid:

• the dilute acid reacts with active metals with the release of hydrogen
• less active metals react only upon heating
• noble metals do not react

6. Interaction with nitric acid

With nitric acid:

• hydrogen is usually not released
• nitrogen oxides are formed
• the acid exhibits strong oxidizing properties

7. General conclusion

• The activity of metals decreases from left to right
• Metals before hydrogen displace it from acids
• Noble metals (Cu, Ag, Au, etc.) hardly react with acids
• The ability of ions to accept electrons increases from right to left

Thus, a metal's position in the activity series determines its chemical properties.

Note that under normal conditions, all s-element metals react with water, except beryllium and magnesium. Magnesium reacts with water upon heating. Aluminum interacts with water at room temperature, but only after the aluminum oxide film has been removed from its surface. In this case, metal hydroxides are formed. The other metals from manganese to hydrogen in the activity series interact with water vapor upon heating, usually forming metal oxides. Metals located in the series of standard potentials after hydrogen do not interact with water under any conditions.

questions

1. Name the physical properties characteristic of metals.
2. List the p-elements that belong to the metal elements.
3. Balance the coefficients in the reaction equation by the electron balance method: Cu + HNO3(dilute) → Cu(NO3)2 + NO↑ + H2O.
4. Write the equations for the possible chemical reactions, given that copper is oxidized to the oxidation state +2:

   а) Ag + НСl →; б) Сu + Hg(NО3)2 → ;

   в) Mg + H2SО4(dilute) →; г) Ni + NaCl → ;

   д) Zn + АgNО3 → ; е) Au + H2O → .

5. Write the equations for the reactions of zinc with nonmetals (O2, P), acids (dilute HCl, H2SO4), alkali solutions (NaOH, KOH), and salts (AgNO3, Pb(NO3)2).
6. Zinc weighing 1.3 g was dissolved in a concentrated solution of sodium hydroxide. Calculate the volume of gas released.
7. Write the equations for the reactions that can take place on the surface of an active metal, for example lithium, in air.
8. Indicate how the mass of a zinc plate will change (increase, decrease, or remain unchanged) when it is immersed for a short time in a solution of: 1) sulfuric acid; 2) sodium hydroxide; 3) magnesium sulfate; 4) copper(II) sulfate; 5) silver(I) nitrate.
9. Determine the volume of hydrogen released when 260 g of zinc reacts with 250 cm3 of a sulfuric acid solution. The mass fraction of H2SO4 is 15 %, and the density is 1.1 g/cm3.
10. An iron plate weighing 90 g was immersed in a solution of copper sulfate. After some time it was removed, rinsed, dried, and weighed. Its mass became 92.4 g. Determine the mass of iron that reacted and the mass of copper deposited on the plate.

Self-check questions

1. In order of increasing reducing activity, the metals are arranged in the series:

• а) Mg, Ca, Na;
• б) Cu, Ag, Hg;
• в) Cа, K, Cs;
• г) Zn, Al, Pb.

2. React with alkali solutions:

• а) Zn;
• б) Ca;
• в) Al;
• г) Be.

3. Reacting with water vapor, they form oxides:

• а) Li;
• б) Ag;
• в) Fe;
• г) Zn.

4. The mass of a zinc plate will increase when it is immersed in a solution of:

• а) Hg(NO3)2;
• б) Cu(NO3)2;
• в) AgNO3;
• г) HNO3.

5. To dissolve 13 g of zinc, a solution containing sodium hydroxide in the following mass (g) is required:

• а) 40;
• б) 20;
• в) 16;
• г) 4.

See also

• [[b13103]]
• [[b13104]]
• [[b13087]]
• [[b13086]]