Chemical Changes Lab

1. Pick Reactant 1 and Reactant 2. One reactant is in the flask. The other one sits next to it.
2. Pick a setup. Normal setup is open to the air. Gas collection catches any gas in a test tube. Closed system seals everything inside a glass box.
3. Before you start, drag the Thermometer and Phenol red to the lab bench. Their cards show the Start temperature and the Start pH.
4. Read the scale. Then press Play (the triangle) to mix the reactants. Look for bubbles, color changes, new solids, light and heat.
5. When the reaction is over, read the scale again. Drag Phenol red to the bench again to find the End pH.
6. In Gas collection, drag the Glowing splint or the Burning splint to the test tube to find out what the gas is.
7. The Lab notebook keeps your readings for each reaction. Press Reset to run a reaction again.

A chemical change makes new substances. The new substances have new properties. A physical change can change how something looks, but it is still the same substance.

Clues that a chemical change happened: a gas forms (bubbles), a color changes, light is given off, a new smell appears, the temperature changes, or a precipitate forms. A precipitate is a solid that appears when two liquids mix.

A clue is not proof. Some solids make water hotter or colder when they dissolve, but no new substance forms. Dissolving is a physical change.

A reaction that gives off heat is exothermic. The temperature goes up. A change that takes in heat is endothermic. The temperature goes down.

Phenol red is an indicator, a dye that changes color with pH. It turns yellow in an acid, stays orange when the liquid is neutral, and turns pink in a base.

In Gas collection, the gas travels through a tube into a test tube full of water. The gas pushes the water out, so you can see how much gas formed.

A glowing splint bursts into flame in oxygen. A burning splint makes a loud pop in hydrogen, because hydrogen burns very fast. A burning splint goes out in carbon dioxide and in other gases that do not let things burn.

The law of conservation of mass says that matter is not created or destroyed in a chemical reaction. The atoms just rearrange into new substances. So the total mass stays the same.

In Normal setup, a gas can float away into the air. Then the scale shows a little less mass at the end. The mass did not disappear. It left with the gas.

In Gas collection or a Closed system, the gas is trapped. Watch the scale stay the same.

Everything on the bench sits on the scale. When the tweezers, a beaker or a dropper is lifted, the scale reads less until it is put back down.