Evidence of a Chemical Reaction & a New Substance

A student mixes 2 clear liquids in a beaker. The mixture becomes cloudy, and a solid forms and settles at the bottom. What is the best conclusion?

• A physical change occurred due to mixing.

• A new substance formed due to a chemical change.

• The liquid froze in the beaker.

• the solid was part of one of the original liquids.

Answer explanation

The formation of a solid and cloudiness indicates a chemical change, suggesting a new substance was created from the reaction of the two liquids, rather than just a physical change or freezing.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

A metal strip is placed in a blue solution. After 10 minutes, the strip has a dark coating and the solution is green. which evidence best supports a chemical change occurred?

• The metal cooled down.

• The liquid became less dense.

• There was a color change and a new substance formed.

• The metal strip sank to the bottom.

Answer explanation

The evidence of a color change from blue to green and the formation of a dark coating on the metal strip indicates a chemical change, as new substances are created during the reaction.

Tags

NGSS.MS-PS1-2

A student stirs baking soda into vinegar and observes fizzing & bubbles rising rapidly. What does this evidence suggest?

• A new gas formed, showing a chemical change.

• A physical change occurred due to movement.

• Baking soda dissolved completely.

• The solution evaporated.

Answer explanation

The fizzing and bubbles indicate a gas is produced when baking soda reacts with vinegar, confirming a chemical change has occurred.

Tags

NGSS.MS-PS1-2

A student places steel wool in a test tube and records an increase in temperature. Which statement best explains this observation?

• A chemical change occurred causing the temperature to rise.

• The steel wool absorbed energy from the air.

• A physical change made the steel expand.

• The test tube was heated from an outside source.

Answer explanation

The increase in temperature indicates a chemical change, as the steel wool reacts with oxygen, releasing energy in the form of heat. This rules out physical changes or external heating as explanations.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

A white powder is dissolved in water. The solution becomes hot and turns yellow. Which evidence suggests a chemical change has occurred?

• Change in temperature and color

• Powder settled at the bottom.

• Water became cloudy.

• Powder did not dissolve fully.

Answer explanation

The change in temperature indicates an exothermic reaction, while the color change to yellow suggests a new substance has formed. Both are clear signs of a chemical change.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

A student combines 2 liquids and notices a strong odor and bubbling. What conclusion can be drawn?

• One liquid evaporated quickly.

• A gas formed, suggesting a chemical change

• A physical change occurred with no new substance

• The liquids were both acidic.

Answer explanation

The strong odor and bubbling indicate that a gas was produced during the reaction, which is a sign of a chemical change. This rules out physical changes and suggests a reaction occurred between the two liquids.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-5

The teacher adds silver nitrate to a solution containing chloride ions. A white solid forms immediately. What is the best explanation?

• The solid was already present in one of the liquids.

• The solution cooled down, forming crystals.

• A physical change occurred during mixing.

• A precipitate formed, showing a chemical change.

Answer explanation

The formation of a white solid indicates a precipitate, which occurs when silver nitrate reacts with chloride ions, resulting in a chemical change. This confirms that a new substance has formed.

Tags

NGSS.MS-PS1-2

A student heats sugar in a pan. The sugar turns brown and gives off smoke. What does this indicate?

• A chemical change occurred as the sugar changed color.

• The sugar melted and re-solidified.

• The sugar absorbed heat and expanded.

• A physical change occurred as sugar evaporated.

Answer explanation

The sugar turning brown and giving off smoke indicates a chemical change, as it undergoes caramelization and produces new substances, evidenced by the color change.

Tags

NGSS.MS-PS1-2

A tablet is placed in water. Bubbles form, and the temperature of the water drops. Which conclusion is best supported by this observation?

• A gas formed and thermal energy was absorbed, showing a chemical change.

• The tablet melted into the water.

• A physical change occurred with no new substance.

• The tablet dissolved but stayed the same substance.

Answer explanation

The formation of bubbles indicates a gas was produced, and the drop in temperature suggests thermal energy was absorbed, indicating a chemical change occurred.

Tags

NGSS.MS-PS1-2

NGSS.MS-PS1-4

A student adds lemon juice to milk. Clumps begin to form in the liquid. What evidence supports that a new substance formed?

• The milk became warm.

• A precipitate formed as proteins clumped together.

• The milk turned completely clear.

• The lemon juice was filtered out.

Answer explanation

A precipitate formed as proteins clumped together indicates a chemical change, showing that a new substance was created. The clumping of proteins is evidence of this transformation, unlike the other options.

Tags

NGSS.MS-PS1-2