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20 questions
Which lab experiments below describe a situation where a chemical change has occurred? Check all that apply.
After adding zinc (Zn) to hydrochloric acid (HCl), a student observes bubbles forming in the solution and a thermometer registers a 10° change in temperature.
A student uses a mortar and pestle (a grinding stone) to break up large pieces of ammonium thiocyanate ( NH4SCN ) into smaller pieces.
After combining Unknown A (a solid, white crystal) with Unknown B (a clear, odorless liquid), there is a strong smell produced and a thermometer registers a 15° change in temperature.
A student dissolves sugar ( C6H6O6 ) into water ( H2O ). The sugar crystals seem to disappear.
A scientist spilled a few drops of dilute hydrochloric acid (HCl) on a lab table. For safety purposes, the scientist sprinkled some baking soda ( NaHCO3 ) onto the spill. Which observation would provide the best evidence that a chemical reaction occured?
The baking soda and hydrochloric acid combined, and bubbles formed.
The baking soda absorbed the hydrochloric acid.
Some of the baking soda dissolved in the hydochloric acid.
The hydrochloric acid evaporated, leaving only the baking soda.
What key words, when present in a question about chemical reactions, might indicate a chemical change is occuring? Check all that apply.
Bubbling
Fizzing
Dissolving
Evaporating
A student combines two clear, colorless solutions shown here. When combined, the temperature changed from 25° to 23° and a white substance rapidly formed and settled at the bottom of the container. What most likely happened to produce these results?
One of the original compounds came out of solution
The solutions reacted chemically
Some of the water froze into ice crystals
Rapid evaporation of water occured, leaving a solid
Which of the following does NOT indicate a chemical reaction is occuring? Check all that apply.
Unknown A dissolves into Unknown B
Unknown A creates fizzing and bubbles when combined with Unknown B
Unknown A sinks to the bottom when added to Unknown B
Unknown A floats to the top when added to Unknown B
Which scientific observation, shown in the chart, indicates that a chemical reaction has NOT occurred?
Number 1
Number 2
Number 3
Number 4
Carbon dioxide ( CO2 ) forms when coal burns in the presence of oxygen. Which of these is the BEST evidence that a chemical reaction occurs when coal burns?
The shape of the coal changes
Oxygen is present
A new substance is produced
Coal is made up of more than one element
Observe the chemical equation shown here. What evidence of a chemical reaction is present when 2NO is added to O2 ?
A gas is present
The total number of atoms remains unchanged
The state of matter remains the same
A brown gas is produced
Which change describes a substance that changes shape, form, or appearance but is still the same substance?
physical change
chemical change
Rust on an iron bar is an example of chemical change.
True
False
Which below are types of physical properties:
density
color change
temperature
mallelable
solubility
Which of the following are examples of chemical properties (more than one)
combusts
reacts with water and oxygen
ductile
is weighed in grams
has a sour taste
Review the data in the chart provided. Which statement below is NOT supported by this data?
A chemical reaction takes place between magnesium and hydrochloric acid.
A gas is released in Test Tube 2.
The substances in both test tubes are reactive.
Energy is released in Test Tube 2.
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