Purpose
To determine the ratio of elements in a chemical compound.
Connections to What You Already Know About in Life
You have been surrounded with chemical compounds your whole life. Did you know that? The simplest ones are compounds, like water, table salt, rust, sugar, or baking soda. Did you know that every single molecule of water has exactly the same atoms in it, in exactly the same ratio? Every single grain of sugar is exactly identical? That’s amazing!
Vocabulary
Compound, ratio, reaction
Background
All matter is made of elements and elements combine to form chemical compounds. Chemical compounds are made of two or more elements combined in a set ratio. A ratio compares two numbers. It tells you the amount of one item compared to the amount of another item. The formula for a chemical compound shows the ratio of the elements in the compound. For example, you are familiar with table salt, a chemical compound made from sodium (Na) and chlorine (Cl). The chemical formula is NaCl. The formula shows that the ratio of sodium atoms to chlorine atoms is 1:1.
You are also familiar with a compound called rust, which is made from iron (Fe) and oxygen (O). The chemical formula for rust is Fe2O3. The small number to the right of each symbol is a subscript. The subscripts tell you that a molecule of rust contains two iron atoms (Fe) combined with three oxygen atoms (O). The ratio of iron atoms to oxygen atoms in rust is 2:3.
When elements combine to form compounds, the compounds have different properties from those of the combining elements. Color is a property that can change in a chemical reaction, so a color change is evidence that a chemical reaction may have occurred.
Procedure Section 1
- To start this activity, click this link for Creating Chemical Compounds. The lab will load in a new tab. Click back to this tab to read further instructions and complete the questions below.
- Double click on a test tube from the box to place it on the metal test tube stand. Click on the bottle of Ag+ solution on the shelf to add it to the test tube. Drag the tube to the blue test tube rack. If you make a mistake in selecting the correct solution, you can drag the test tube to the red disposal bucket and begin again.
- Double click on another test tube from the box. Click on the bottle of Pb2+ solution on the shelf to add it to the test tube. Drag the tube to the blue rack. Repeat this process and create test tubes containing Fe3+ (not Fe2+), Cu2+, Pb2+ (again), and Ag+ (again).
- You can observe color changes that occur in the test tube and see the changes in chemical formulas in Live Data. Hover over the first test tube on the left. Observe that the solution is clear and colorless in the window and that the display shows Ag+.
- Drag the first test tube (Ag+) from the blue test tube rack to the metal clamp on the stand on the lab bench and click the bottle labeled NaCl on the lab bench. Notice the changes in the test tube and in the screen. The solution changes from colorless to white and the display shows AgCl. In this compound the ratio of Ag to Cl is 1:1. Record the formula, the color before reaction, the color after reaction, and the ratio in the first row of the table below. Drag the test tube to the red disposal bucket.
- Drag the second test tube (Pb2+) from the blue rack to the metal stand and click the bottle labeled NaCl. What changes do you observe in the test tube and in the display? Record the color before, the color after, and the ratio in the 2nd row of the table. Drag the test tube to the red disposal bucket.
- Drag the third test tube (Fe3+) from the blue rack to the metal stand but this time click the bottle labeled Na2S. Record the color before, the color after, and the ratio in the table below. Drag the test tube to the red disposal bucket. Repeat for the fourth (Cu2+) and fifth (Pb2+) test tubes adding Na2S in each case. Record the color before, the color after, and the ratio in the table below. Drag the test tubes to the red disposal bucket.
When entering subscripts and superscripts you will use “_” and “^” respectively. For example, AbC is entered as A_b^c
