Chemical Change

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  $10\degree$  change in temperature.

• A student uses a mortar and pestle (a grinding stone) to break up large pieces of ammonium thiocyanate ( $NH_4SCN$  ) 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  $15\degree$  change in temperature.

• A student dissolves sugar ( $C_6H_6O_6$  ) into water ( $H_2O$  ). 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 ( $NaHCO_3$  ) 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  $25\degree$  to  $23\degree$  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 (  $CO_2$  ) 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  $O_2$  ?

• A gas is present

• The total number of atoms remains unchanged

• The state of matter remains the same

• A brown gas is produced

A solid piece of chocolate is melted and changed to liquid form. Which property of the piece of chocolate will remain the same?

• Texture
• Temperature
  
• Shape
•  Mass

Tags

NGSS.MS-PS1-4

NGSS.MS-PS1-5

Which of the following is NOT an example of a physical change?

• crumpled paper
• pencil sharpening
• shrunken clothing
• rust