Question

b. the iron comes from the rock. where does the oxygen come from? (the air/rain)

1. the chemical name for rust is (carbon oxide/iron oxide)
2. what kind of weather speeds rusting? (cold and dry/warm and moist)
3. rusting is an example of weathering. (mechanical/chemical)
4. what dissolved in the limestone to form the caves shown in figure b? (carbon dioxide/carbonic acid)
5. carbonic acid forms when (carbon dioxide/oxygen) combines with (iron/water)
6. carbon dioxide comes from (water/the air)
7. the dissolving of limestone is an example of weathering. (chemical/mechanical)
8. chemical weathering change the chemicals in rocks. (does/does not)
9. chemical weathering form new products. (does/does not)

Explanation:

• For the question about where oxygen comes from in rusting, air contains oxygen which reacts with iron.
• Rust is iron oxide ($Fe_2O_3$), not carbon oxide.
• Warm and moist conditions speed up the chemical reaction of rusting (iron reacting with oxygen and water).
• Rusting is a chemical change (iron + oxygen + water → iron oxide), so it's chemical weathering.
• Carbonic acid ($H_2CO_3$) dissolves limestone ($CaCO_3$) to form caves. Carbon dioxide ($CO_2$) alone doesn't dissolve limestone as effectively in the context of cave - formation.
• Carbonic acid forms when carbon dioxide ($CO_2$) reacts with water ($H_2O$) ($CO_2 + H_2O

ightleftharpoons H_2CO_3$).

• Carbon dioxide is present in the air.
• The dissolving of limestone (a chemical reaction: $CaCO_3 + H_2CO_3

ightarrow Ca(HCO_3)_2$) is chemical weathering.

• Chemical weathering changes the chemicals in rocks through chemical reactions.
• Since chemical weathering changes the chemical composition of rocks, it forms new products.

Answer:

1. the air
2. iron oxide
3. warm and moist
4. chemical
5. carbonic acid
6. carbon dioxide; water
7. the air
8. chemical
9. does
10. does