Question

questions, page 1
which one of the following changes involving water is a chemical change?
a) sugar dissolves in water
b) pure sodium reacts with water to make h₂ gas
c) water boils at 100-degrees celsius
d) water has a density of 1 g/ml
answer:

which one of the following is the best indication that a chemical change has occurred?
highlight your answer.
a) changing shape
b) melting
c) evaporation
d) change in color
answer:

Explanation:

First Question (Chemical Change Involving Water)

Step1: Analyze Option a

Sugar dissolving in water is a physical change (dissolution, no new substance).

Step2: Analyze Option b

Sodium reacting with water produces \( \ce{H2} \) gas (new substance formed, chemical reaction).

Step3: Analyze Option c

Water boiling is a physical change (state change, no new substance).

Step4: Analyze Option d

Density is a physical property, not a change.

Second Question (Indication of Chemical Change)

Step1: Analyze Option a

Changing shape is a physical change (e.g., bending a wire).

Step2: Analyze Option b

Melting is a physical change (state change, solid to liquid).

Step3: Analyze Option c

Evaporation is a physical change (liquid to gas).

Step4: Analyze Option d

Change in color often signals a chemical reaction (e.g., rusting, color change in reactions).

Answer:

s:
First Question: b) Pure sodium reacts with water to make \( \ce{H2} \) gas
Second Question: d) Change in color