Mystery Lab
A student combines two clear liquids. The mixture immediately begins producing bubbles. What evidence suggests a chemical change occurred?
Production of a gas
True or False: A chemical change ALWAYS produces a new substance.
True
A bicycle chain turns reddish-brown over time. What evidence of chemical change is shown?
Color Change
What is a precipitate?
a solid forming in liquids
What type of change creates a new substance?
Chemical Change
A student combines two liquids at 24°C. After mixing, the temperature decreases to 16°C. What evidence of a possible chemical change is observed?
Change in thermal energy.
Jamie made koolaid by mixing sugar, water, and blue flavored powder. Is this a physical or chemical change andwhy?
Physical change. No new substance was formed
Old food develops a rotten odor. What evidence of chemical change is shown?
New Smell
What is thermal energy change?
Something changing temperature without adding or taking away heat. (Not putting it in freezer or on stove)
Sand and water are mixed together; the water now looks brown. What type of change is this?
Physical, no new substance is created
A student mixes a clear liquid with a yellow liquid. A thick, white solid forms and settles at the bottom. What evidence indicates that a new substance may have formed?
Formation of a precipitate.
A student heats water until it boils. Is this evidence of a chemical change?
No, boiling is a physical change
A campfire is burning. Name 2 pieces of evidence of a chemical change.
gas production, thermal energy change, color change
an unexpected color appears. not adding color to something though
An unknown solid has a mass of 60 g and a volume of 20 mL. What is its density?
3 g/mL
Three experiments are performed: Which experiment provides evidence of a chemical change, and why?
Experiment A: A solid is crushed into smaller pieces.
Experiment B: Two liquids are mixed, producing a new odor.
Experiment C: A liquid is placed in a freezer and becomes solid.
Experiment B, because a new smell was produced.
Which TWO are chemical changes: burning wood, melting ice, rusting metal, or cutting paper?
Burning wood and rusting metal.
Chocolate melts as it is warmed up and its smell becomes stronger. Is this a physical or chemical change?
Physical, the smell was already there, and the chocolate is still chocolate.
It shows the formation of a gas
A student finds a shiny element that conducts electricity but breaks easily when struck. Which classification best fits this element?
Metalloid
Two liquids are mixed. A yellow solid forms, and it now smells sour. Name TWO pieces of evidence of chemical change.
Precipitate formation and new smell.
A student says, "If a solid forms during an experiment, it must be a chemical change." What is wrong with this statement?
Freezing or solidifying can form a solid without creating a new substance.
Which TWO are chemical changes: tarnishing silver, freezing water, browning fruit, or crumpling foil?
Tarnishing silver and browning fruit.
Give an example of each type of chemical change for our acronym:
PLEASE EXCUSE COUGHS BURPS and SNEEZES
precipitate, energy change, color change, bubbles or gas, smell change
A student has a mixture of oil and water that don't mix well together. What type of mixture is it and why, and why do the substances layer together rather than mixing?
Heterogeneous because the liquids form separate layers and you can see the separate parts, and they have different densities.