Question

true/false – physical vs chemical changes

1. when ice melts into liquid water, the solid turns into a liquid without changing its chemical composition. this is a physical change. (t/f)
2. when wood burns in a fireplace, it produces ash, smoke, and heat, and new substances are formed. this is a chemical change. (t/f)
3. dissolving sugar in water changes only the physical state, but the sugar molecules remain the same. therefore, dissolving sugar is a chemical change. (t/f)
4. rust forms on iron when it reacts with oxygen over time. this process changes the chemical composition of the iron. rusting is therefore a physical change. (t/f)
5. freezing liquid water into ice changes the form of water but does not change its chemical composition. this is a chemical change. (t/f)
6. when a cake is baked in the oven, heat causes ingredients to chemically react and form new substances. baking a cake is a chemical change. (t/f)

\what am i?\ riddles

1. i am a substance made of two hydrogen atoms and one oxygen atom. people drink me every day to survive. what am i?
2. i form slowly when iron or metal reacts with oxygen in the presence of water, leaving a reddish - brown coating that weakens the metal over time. what am i?
3. i can mix completely with water but my chemical structure stays the same, so no new substance is formed. what am i?
4. i am a colorless gas made of one carbon atom and two oxygen atoms. humans exhale me, and plants use me during photosynthesis. what am i?
5. i am a pure substance that cannot be broken down into simpler substances. i am found on the periodic table. what am i?

short answer

1. a student mixes vinegar and baking soda in a science experiment. describe the type of change that occurs, explain why it is that type, and list any evidence you can observe to support your answer.

Explanation:

1. Melting ice is a physical change as only state changes, not chemical composition.
2. Burning wood forms new substances like ash, smoke and heat, so it's a chemical change.
3. Dissolving sugar in water is a physical change as sugar molecules remain the same, not a chemical change.
4. Rusting of iron is a chemical change as it changes iron's chemical composition, not a physical change.
5. Freezing water is a physical change as only state changes, not a chemical change.
6. Baking a cake involves chemical reactions forming new substances, so it's a chemical change.

For riddles:

1. Water has the formula H₂O and is essential for survival.
2. Rust is formed by iron - oxygen - water reaction and has a reddish - brown color.
3. Substances that dissolve in water without chemical change could be salt (e.g.).
4. Carbon dioxide (CO₂) is exhaled by humans and used by plants in photosynthesis.
5. Elements are pure substances on the periodic table that can't be broken down further.

For the short - answer question: When vinegar (acetic acid) and baking soda (sodium bicarbonate) are mixed, a chemical change occurs. This is because a chemical reaction takes place, producing carbon dioxide gas, water, and a salt (sodium acetate). Evidence includes the formation of bubbles (due to carbon dioxide gas being released).

Answer:

1. True
2. True
3. False
4. False
5. False
6. True

Riddles:

1. Water
2. Rust
3. Salt (or other soluble substance that doesn't react chemically with water)
4. Carbon dioxide
5. Element

Short - answer: A chemical change occurs. Reason: A chemical reaction between acetic acid in vinegar and sodium bicarbonate in baking soda produces carbon dioxide gas, water, and sodium acetate. Evidence: Formation of bubbles (carbon dioxide gas release).