Limewater + Carbon Dioxide Yields Calcium Carbonate (chalk) + Water
Baking Soda + Vinegar Yields Carbon Dioxide + Water + Sodium Acetate + Carbonic acid
Phenolphthalein/Water and Baking Soda mixed together then add Calcium Chloride! Wow!
Chemical changes result in the formation of one or more new substances with new chemical and physical
properties. Evidences that a chemical change may have occurred include:
● Color change
○ When a substance changes color, the chemical composition of the substance may have
changed (for example, iron turns to a reddish-brown when it rusts, clothes change color when bleach is
added, apples turn brown when they react with oxygen in the air, or marshmallows turn black when
burned).
○ It is possible to have a color change without a chemical change (for example, adding food
coloring to water).
● Temperature change
○ When a substance is combined with another substance, there may be an increase or
decrease in temperature (for example, when wood burns to ash and gases, the temperature increases).
○ It is possible to have a temperature change without a chemical change usually due to a
heat source (for example, warming of the water in a pot).
● Formation of a precipitate
○ When two solutions are combined, they may form a new solid substance. This solid
substance is called a precipitate and indicates that a chemical change has occurred.
○ For example when carbon dioxide is combined with aqueous calcium hydroxide
(limewater), solid calcium carbonate (chalk) is formed as the precipitate.
○ The precipitate may be in the form of very small particles, appearing as cloudiness in the
solution or as a solid which settles to the bottom of the container.
● Formation of a gas
○ When solid or liquid substances are combined, they may form gas bubbles or smoke
indicating that a chemical reaction has taken place.
○ For example when vinegar is added to baking soda, it forms carbon dioxide bubbles.
○ It is possible to form gas without a chemical change (for example, when water is heated
to boiling).
