Question

or a chemical change.

the previous demonstrations, fill in the table below with your observations.

\

$$\begin{tabular}{|l|l|l|l|l|} \\hline ion & activity & expected observation & type of change (physical/chemical) & indicator (if chemical) \\\\ \\hline & ice melts in hand & & & \\\\ \\hline & sugar dissolves in water & & & \\\\ \\hline & mixing vinegar and baking soda & & & \\\\ \\hline & burning a candle wick & & & \\\\ \\hline & crushing chalk stick & & & \\\\ \\hline & apple slice turns brown & & & \\\\ \\hline \\end{tabular}$$

Explanation:

🆕 New Concept Discovered: Physical vs. Chemical Changes
Identifying if a substance changes its identity or just its form.

Step 1: Understand the Difference between Physical and Chemical Changes

To fill out the table, we need to distinguish between two types of changes:

• Physical Change: The substance changes its physical state, shape, or appearance, but its chemical identity remains exactly the same. No new substances are formed. Examples include phase changes (melting, freezing) and dissolving.
• Chemical Change: The substance reacts to form entirely new chemical substances with different properties.
• Indicators of a Chemical Change: Common signs include gas production (bubbling/fizzing), temperature change (release or absorption of heat), light production, unexpected color change, or the formation of a precipitate (solid).

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Step 2: Analyze Each Activity

Let's look at each activity one by one to determine the expected observation, the type of change, and any chemical indicators:

1. Ice melts in hand

• Observation: Solid ice turns into liquid water due to body heat.
• Type of Change: Physical. It is a phase change from solid to liquid; the chemical formula remains \( \text{H}_2\text{O} \).
• Indicator: N/A (Not a chemical change).

1. Sugar dissolves in water

• Observation: The solid white sugar crystals disappear into the water, forming a clear solution.
• Type of Change: Physical. Dissolving is a physical process because the sugar molecules are simply dispersed among water molecules; no new chemical bonds are formed, and the sugar can be recovered by evaporating the water.
• Indicator: N/A.

1. Mixing vinegar and baking soda

• Observation: Rapid bubbling, fizzing, and foaming occur.
• Type of Change: Chemical. An acid-base reaction occurs between acetic acid and sodium bicarbonate, producing carbon dioxide gas, water, and sodium acetate.
• Indicator: Gas production (bubbling/fizzing).

1. Burning a candle wick

• Observation: A flame appears, smoke is released, and the white/black cotton wick turns into black ash.
• Type of Change: Chemical. Combustion is a chemical reaction where the wick reacts with oxygen to produce carbon dioxide, water vapor, and carbon (ash).
• Indicator: Production of light/heat, color change (to black), and gas/smoke production.

1. Crushing chalk stick

• Observation: The solid chalk stick breaks down into a fine white powder.
• Type of Change: Physical. Only the shape and size of the chalk have changed; it is still chemically calcium carbonate (\( \text{CaCO}_3 \)).
• Indicator: N/A.

1. Apple slice turns brown

• Observation: The exposed white flesh of the apple turns a brownish color over time.
• Type of Change: Chemical. This is enzymatic browning, where compounds in the apple react with oxygen in the air to form new brown pigments (melanins).
• Indicator: Unexpected color change.

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Answer:

Here is the completed table based on the analysis:

Activity	Expected Observation	Type of Change (Physical/Chemical)	Indicator (If Chemical)
Sugar dissolves in water	White crystals disappear, forming a clear liquid	Physical	N/A
Mixing vinegar and baking soda	Rapid fizzing, bubbling, and foaming	Chemical	Gas production (bubbling)
Burning a candle wick	Flame, smoke, and the wick turns to black ash	Chemical	Production of light/heat, color change
Crushing chalk stick	Solid stick breaks into a fine white powder	Physical	N/A
Apple slice turns brown	The white flesh of the apple turns brown	Chemical	Unexpected color change