Question

1. a student notices that sugar, when heated over a flame, turns black. what the best indication that a new substance is being formed?

a. the sugar melted within the test tube
b. the temperature of the test tube increased.
c. the color of the sugar changed to black
d. the mass of the sugar decreased

1. in which of the following examples has a chemical reaction occurred?*

a. after putting liquid batter into a hot pan, the batter solidifies and begins to turn brown.
b. after turning on a blender filled with fruits, the fruit is chopped up and mixed together.
c. after taking a tray filled with ice cubes out of the freezer, the cubes begin to melt
d. after adding a spoonful of sugar to a mug of hot coffee, the sugar dissolves completely.

1. examine the following chemical reaction: *

h2o2 ---> h2o + o2
what are the products?

Explanation:

• Question 17: A chemical change (new substance formation) often shows signs like color change. Melting (A) is physical. Temperature increase (B) could be physical. Mass decrease (D) might be due to evaporation (physical). Color change (C) is a strong sign of chemical change (new substance).
• Question 12:
• A: Batter turning brown (like sugar in 17) shows a chemical reaction (new substance, browning from Maillard reaction).
• B: Blending fruits is physical (no new substance, just mixing).
• C: Ice melting is physical (state change).
• D: Sugar dissolving is physical (solution formation, no new substance).
• Question 10: In a chemical reaction \(A

ightarrow B + C\), \(B\) and \(C\) are products. For \(H_2O_2
ightarrow H_2O+O_2\), \(H_2O\) (water) and \(O_2\) (oxygen) are products.

Answer:

1. C. The color of the sugar changed to black
2. A. After putting liquid batter into a hot pan, the batter solidifies and begins to turn brown
3. \(H_2O\) (water) and \(O_2\) (oxygen)