Worksheet: Rusting

In this worksheet, we will practice explaining the conditions necessary for rusting and writing balanced equations for the key reactions involved.

Q1:

When an iron nail reacts with oxygen and water in the air, it rusts. What happens then to the total mass of the nail?

  • AIt decreases.
  • BIt increases.
  • CIt stays the same.

Q2:

What is the name of the most abundant oxide produced by the rusting of iron?

  • AIron(V) oxide
  • BIron(IV) oxide
  • CIron(II) oxide
  • DIron(III) oxide
  • EIron(I) oxide

Q3:

Acid rain is produced when sulfur dioxide in the atmosphere reacts with water to form sulfuric acid. Increasing the acid concentration in rain causes an exposed iron surface to rust more quickly. Which of the following is not a mechanism by which dissolved acid accelerates rusting?

  • AHydrogen ions react with iron and oxygen to form iron ions.
  • BDissolved ions increase the conductivity of water.
  • CHydrogen ions react with protective surface coatings.
  • DMetallic iron is made more soluble by a decrease in pH.
  • EThe products of rusting are made more soluble by a decrease in pH.

Q4:

In which of the following environments would rusting of a steel plate occur most rapidly?

  • AOcean floor
  • BFrozen soil
  • CRain forest
  • DRiver bed
  • EDesert

Q5:

Two sealed iron tanks, 𝐴 and 𝐵, contain identical volumes of water at room temperature. Tank 𝐴 contains water that was boiled before being placed in the tank, while the water in tank 𝐵 was not boiled. How and why does the rate of rusting differ between the two tanks?

  • AThe rate of rusting is lower in tank 𝐴 as boiling of water reduces the amount of dissolved salt.
  • BThere is no difference in the rate of rusting.
  • CThe rate of rusting is lower in tank 𝐴 as boiling of water reduces the amount of dissolved oxygen.
  • DThe rate of rusting is higher in tank 𝐴 as boiling of water increases the amount of dissolved oxygen.
  • EThe rate of rusting is higher in tank 𝐴 as boiling of water reduces the amount of dissolved salt.

Q6:

Rusting of iron is an example of an oxidation reaction. The rate of rusting of iron in water varies with increasing salt concentration.

Which particles are removed from a metal during an oxidation reaction?

  • ANeutrons
  • BOxygen atoms
  • CElectrons
  • DProtons
  • EHydrogen atoms

How and why does the rate of rusting of iron in water vary with increasing salt concentration?

  • AThe rate increases because dissolved ions aid the movement of charge.
  • BThe rate increases because dissolved ions aid the decay of metal nuclei.
  • CThe rate increases because dissolved ions react with the metal atoms.
  • DThe rate decreases because dissolved ions aid the ionization of water.
  • EThe rate decreases because dissolved ions react with dissolved oxygen.

Which term best describes the role of the salt solution in the rusting process?

  • AAcid
  • BElectrolyte
  • CReducing agent
  • DOxidizing agent
  • EBase

Q7:

Iron(III) hydroxide is a key product of rusting in humid conditions. This solid material forms from dissolved Fe3+ ions, which in turn are formed from solid iron. The reactions involve water, hydrogen ions (H)+, and oxygen molecules. Each step of the reaction can be represented using a net ionic equation, which is balanced based on the total charge on the two sides of the equation being equal.

Including state symbols, give a balanced net ionic equation for the formation of Fe3+ ions from metallic iron and dissolved hydrogen ions and oxygen molecules.

  • A 4 F e ( ) + 1 2 H ( ) + 3 O ( ) 4 F e ( ) + 6 H O ( ) s a q a q a q l + 2 3 + 2
  • B 4 F e ( ) + 6 H ( ) + 3 O ( ) 4 F e ( ) + 3 H O ( ) s a q a q a q l + 2 3 + 2
  • C 2 F e ( ) + 4 H ( ) + O ( ) 2 F e ( ) + 2 H O ( ) s a q a q a q l + 2 3 + 2
  • D 2 F e ( ) + 6 H ( ) + O ( ) 2 F e ( ) + 3 H O ( ) s a q a q a q l + 2 3 + 2
  • E 4 F e ( ) + 1 2 H ( ) + 3 O ( ) 4 F e ( ) + 3 H O ( ) s a q a q a q l + 2 3 + 2

Including state symbols, give a balanced net ionic equation for the formation of iron(III) hydroxide from Fe3+ ions and water molecules.

  • A F e ( ) + 6 H O ( ) F e ( O H ) ( ) + 6 H ( ) 3 + 2 3 2 a q l s g
  • B F e ( ) + 3 H O ( ) F e ( O H ) ( ) + 3 H ( ) 3 + 2 3 + a q l s a q
  • C 2 F e ( ) + 6 H O ( ) 2 F e ( O H ) ( ) + 3 H ( ) 3 + 2 3 2 a q l s g
  • D 2 F e ( ) + 3 H O ( ) 2 F e ( O H ) ( ) + 3 H ( ) 3 + 2 3 + a q l s g
  • E F e ( ) + 3 H O ( ) F e ( O H ) ( ) + 6 H ( ) 3 + 2 3 + a q l s a q

How many hydrogen ions are consumed in total when an atom of iron is converted to iron(III) hydroxide?

Iron(III) hydroxide can be dehydrated to produce a material containing no hydrogen atoms. How many water molecules are removed for every atom of iron in the material?

Q8:

Vehicles on major roads are found to rust much more rapidly in cold wet countries when the temperature is below freezing. Which factor is most directly responsible for this effect?

  • ASalt
  • BOxygen
  • CpH
  • DTemperature
  • EHumidity

Q9:

A steel chain submerged in water is susceptible to rusting. What effect is observed if sodium chloride is added to the water to produce a saturated solution?

  • AThe steel chain reacts to produce a sodium-iron alloy.
  • BNo rusting takes place.
  • CThe steel chain rusts more quickly.
  • DThe steel chain reacts to form a chloride salt.
  • EThe steel chain rusts less quickly.

Q10:

Which of the following is not a role played by water when iron rusts in neutral water?

  • AWater is incorporated into the final solid material.
  • BWater reacts with iron to form hydrogen molecules.
  • CWater dissolves oxygen gas.
  • DWater dissolves iron ions.
  • EWater reacts with oxygen to generate hydroxide ions.

Q11:

The density of iron is 7.87 g/cm3. When iron is oxidized during rusting, the density decreases to 5.24 g/cm3. By contrast, the density of aluminum is 2.70 g/cm3 and this value increases to 3.99 g/cm3 when the metal is completely oxidized.

What is the percentage change in volume when iron is converted completely to rust? Assume that no water is present at the end of the reaction.

What is the percentage change in volume when aluminum is completely oxidized?

Changes in volume during oxidation affect the amount of cracking caused by oxidation. How do the volume changes of iron and aluminum differ, and what effect does this difference have on the amount of cracking?

  • AAluminum expands more than iron when oxidized, so less cracking occurs.
  • BUnlike iron, aluminum contracts when oxidized, so less cracking occurs.
  • CAluminum expands less than iron when oxidized, so less cracking occurs.
  • DAluminum expands less than iron when oxidized, so more cracking occurs.
  • EUnlike iron, aluminum contracts when oxidized, so more cracking occurs.

Q12:

Why does rusting affect iron more than aluminum?

  • AAluminum binds to water less strongly.
  • BAluminum oxides are less soluble than iron oxides.
  • CAluminum oxides are less stable than iron oxides.
  • DAluminum is protected by a surface oxide layer.
  • EAluminum is less reactive than iron.

Q13:

Give a balanced chemical formula for the formation of the major iron oxide compound in rust.

  • A 2 F e + O 2 F e O 2
  • B F e + O F e O 2 2
  • C 3 F e + 2 O F e O 2 3 4
  • D 4 F e + 3 O 2 F e O 2 2 3
  • E 3 F e + O F e O 2 3 2

Q14:

Two moles of iron react with one mole of oxygen molecules to produce a colored compound of uniform composition. All of the iron reacts and there are no other products.

What is the formula of the compound produced?

  • A F e O 3 4
  • B F e O
  • C F e O 2
  • D F e O 3 2
  • E F e O 2 3

What color is the compound produced?

  • ARed
  • BBlack
  • CYellow
  • DWhite
  • EGreen

The compound reacts with further oxygen to form a more stable material. What color is the new material?

  • AYellow
  • BGreen
  • CWhite
  • DRed
  • EBlack

Q15:

A thin 25.0 kg sheet of iron rusts in wet air containing excess oxygen. The iron is uniformly converted to a single material consisting of iron, oxygen, and water. The material contains 1 molecule of water for every 2 iron atoms reacted.

What mass of oxygen reacts with the iron during this process?

To 3 significant figures, what is the iron content of the product as a percentage of the total mass?

Q16:

When rust is formed on the surface of iron, it does not prevent further oxidation of the remaining metal. What is the main reason that rust does not behave as a protective coating?

  • ARust forms a thin layer on the iron surface and is easily dissolved.
  • BRust forms flakes that adhere weakly to the iron surface.
  • CRust accelerates oxidation by lowering the pH at the iron surface.
  • DRust reacts with metallic iron, catalyzing its own formation.
  • ERust accelerates oxidation by binding to water in the air.

Q17:

A shiny iron nail will rust over time. As it rusts, what happens to the total mass?

  • AIt stays the same.
  • BIt decreases.
  • CIt increases.

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