Chemical Change Lab Report

experiment

A research method in which an investigator manipulates one or more factors to observe the effect on some behavior or mental process

Scientific Method

A series of steps followed to solve problems including collecting data, formulating a hypothesis, testing the hypothesis, and stating conclusions.

scientific design

a procedure to create a fair test of a hypothesis. a completely fair test is one that shows no bias or favoritism toward any variable, whether controlled or uncontrolled, within the experiment.

Observation

the action or process of observing something or someone carefully or in order to gain information.

What color change was observed in the overall reaction of the substances? Do the control experiments provide any evidence concerning the interaction(s) responsible for the color change in experiment 1?

In the overall reaction in Part A, the color changed from red to yellow. Mixing either of the solids with phenol red did not produce a color change. A slight color change was noted when phenol red was mixed with water. The red color faded to a paler shade of redorange. The control experiments suggest, but do not prove, that the color change to yellow in the overall reaction is due to the production of a new substance with new acid-base properties.

Based on the results of the control experiments (2 through 9) what interaction among the 4 substances seems to be responsible for the observed temperature change in the overall reaction (reaction #1)?

Mixing calcium chloride with water (either alone or in a solution of phenol red) produced the same temperature change as was observed for the overall reaction. A great deal of heat was produced and the mixture felt very hot to the touch.

chemical versus physical change

The difference between a physical reaction and a chemical reaction is composition. In a chemical reaction, there is a change in the composition of the substances in question; in a physical change there is a difference in the appearance, smell, or simple display of a sample of matter without a change in composition.

Does the formation of gas bubbles occur independently of the observed temperature and color change? Explain

The formation of gas bubbles occurs independently of the color change, that is, it was observed in a controlled experiment with three substances, calcium chloride, sodium bicarbonate, and water in the absence of the phenol red indicator. It is possible, therefore, that the gas bubbles make the solution turn yellow. Gas bubbles were always observed along with the large temperature increase, which was also observed when calcium chloride alone reacted (dissolved) with water. It is not possible, therefore, to conclude whether a temperature increase was also associated with the production of the gas.

Is there any evidence that a new chemical substance is produced in the overall chemical reaction (#1)? Explain. What interaction among the 4 components must be responsible for the new substance?

The strongest evidence for the production of a new chemical substance comes from the formation and release of gas bubbles when calcium chloride and sodium bicarbonate are mixed together in a liquid. Since the fizzing is not observed when either solid alone dissolves in water, even though the temperature changes, there is a good likelihood that the gas represents a new chemical substance. In order to answer this question precisely, however, it would be necessary to isolate the gas and study its properties. If it has different properties than any of the other substances, then it is a new chemical substance. The color change to yellow also suggests that a new substance is produced (it may be the gas!) which has different acid-base properties than the reactants. The new substance must be formed from "rearranging" the elements in the two solids, because either solid alone with water or phenol red failed to give either gas bubbles or a color change.

What control experiments were done to evaluate if a liquid is necessary for the observed effects in experiment 1? Does any reaction occur in the absence of water?

The two solids were mixed without any liquid (phenol red or water) present. No evidence of any reaction was observed. The two solids seemed to retain their individual appearance in the mixture of the two.

Was there a temperature effect observed in any of the individual control experiments that wasn't observed in the overall reaction of the 4 chemical substances? Explain

When sodium bicarbonate was mixed with water (either alone or in a solution of phenol red), some of the solid dissolved and the solution felt slightly cool to the touch. This temperature decrease, due to the solution absorbing heat energy, was not observed in the overall reaction.

chemical reactions

change substances into different substances by breaking and forming chemical bonds