Question

1. what happens when an ice cube melts in a beaker of water?

a. the temperature of the water did not change.
b. the water cools down and changes to a new substance.
c. a physical change occurs because the ice changes from a solid to a liquid.
d. a chemical change occurs because the ice changes from a solid to a liquid.

1. hydrogen (h) and oxygen (o) are pure substances. each is made of only one type of atom, but hydrogen atoms are different from oxygen atoms. hydrogen and oxygen chemically combine to form water (h₂o).

based on this information, which statement is true?
a. hydrogen, oxygen, and water are all elements.
b. hydrogen, oxygen and water are all molecules.
c. hydrogen and oxygen are elements, and water is a molecule.
d. hydrogen is an element and oxygen and water are molecules.

Explanation:

• Question 13:
• Melting of ice is a physical change as it involves a change in state (solid to liquid) without forming a new substance.
• Option A is incorrect as the temperature of the surrounding water may change (it cools down as ice absorbs heat for melting).
• Option B is wrong because water doesn't change to a new substance during ice - melting.
• Option D is incorrect as it is a physical, not a chemical change.
• Question 14:
• Hydrogen (\(H\)) and oxygen (\(O\)) are elements (pure substances made of only one type of atom).
• Water (\(H_2O\)) is a molecule (formed by the chemical combination of hydrogen and oxygen atoms).
• Option A is wrong as water is not an element.
• Option B is incorrect as hydrogen and oxygen are elements (not just molecules in the context of being pure substances).
• Option D is wrong as oxygen is also an element.

Answer:

1. C. A physical change occurs because the ice changes from a solid to a liquid.
2. C. Hydrogen and oxygen are elements, and water is a molecule.