Physical and Chemical Changes

When sulfuric acid is poured onto sugar, the sugar turns black, a gas is given off, and the temperature increases. These signs of a chemical reaction are evidence that which of the following is happening? A The sugar is becoming coal. B A new substance is being formed. C The acid is turning into a base. D All of the above

A new substance is being formed.

During an investigation, students mixed together two clear solutions in a test tube. The students then observed the changes that occurred. A student concluded that a chemical change occurred. Which observation best supports this conclusion? A The color of the solid substance is yellow. B A precipitate was produced from the solutions. C The solutions became clear after they were mixed. D None of these

A precipitate was produced from the solutions.

A white powder is placed into a cup containing a clear solution. Which of the following changes gives the best evidence that a chemical change is happening? A The powder dissolves into the clear solution. B Some of the white powder sinks to the bottom of cup. C After the powder and the solution combine, bubbles form. D Some of the clear solution evaporates from the cup.

After the powder and the solution combine, bubbles form.

Students in a science classroom perform investigations using different solutions. During each investigation two solutions are mixed and the students make observations. Which of the following observations would provide the least evidence that a chemical reaction had occurred after the solutions were mixed? A Bubbles began to form after the solutions were mixed. B The solutions were slow to mix because they had different densities. C After the solutions mixed, a change in color was observed. D An increase in temperature was recorded after the solutions were mixed.

B The solutions were slow to mix because they had different densities.

A student mixed two clear solutions together, but she did not notice any obvious changes in the solutions. Both solutions remained clear, and no new gaseous or solid substances were observed. The student is still not sure if a chemical change occurred when the solutions were mixed. Which of the following procedures would provide the best evidence to determine if a chemical change occurred? A Measure the mass before and after the solutions mixed. B Measure the total volume of solutions before and after they are mixed. C Measure the temperature of the solutions before and after they are mixed. D Measure the conductivity of these solutions before and after they are mixed.

C Measure the temperature of the solutions before and after they are mixed.

A teacher placed some vinegar (acetic acid) into a beaker. She then placed a scoop of baking soda (sodium bicarbonate) into the same beaker. Which of these observations gives the best evidence that a chemical change occurred? A Some baking soda dissolved in the vinegar. B Vinegar evaporated and could be smelled in the room. C The baking soda and vinegar mixed and produced bubbles. D A portion of the baking soda sank to the bottom of the beaker.

C The baking soda and vinegar mixed and produced bubbles.

Zinc is an element that can chemically react with other substances. When zinc reacts with hydrochloric acid, zinc chloride is produced. Which observation best supports the conclusion that a chemical reaction has occurred between zinc and the acid? A Zinc is an element. B Acids are a safety hazard. C A new substance is formed. D None of these

C. A new substance is formed.

A group of students make observations about the changes that occur to a candle as it burns. A table of their observations is shown below. Based on these observations, the students decide that a chemical change is occurring. Which observation provides the least evidence that the burning candle is undergoing a chemical change? A. Light given off from the flame B. Heat being released from the candle C. The wax around the wick is melting D. Gases are being produced.

C. The wax around the candle is being melted.

Students were given 4 different solid substances during an investigation on physical and chemical changes. They placed each substance into a beaker of acid and recorded their observations. Which description of the solid substance is the least likely to have undergone a chemical change?

The solid substance completely dissolved after 5 minutes

Sodium hydroxide and hydrochloric acid solutions are both clear. When the 2 mix , a pink solution is created. What most likely happened to produce these results?

The solutions reacted chemically.