# Stoichiometry Activities

Instructor: Rachel Tustin

Dr. Rachel Tustin has a PhD in Education focusing on Educational Technology, a Masters in English, and a BS in Marine Science. She has taught in K-12 for more than 15 years, and higher education for ten years.

Stoichiometry isn't the easiest topic for teachers to teach or for students to master in chemistry. However, it is an easy topic to scaffold with students and make relevant to their lives and experiences.

As a chemistry teacher, stoichiometry is a challenging subject to teach. It's a lot of math, a lot of fractions, and involves perhaps student's least favorite topic in chemistry: balancing equations. However, even though students will have to delve into the math, you can make stoichiometry fun and hands on.

### Baking Soda Stoichiometry Challenge

Stoichiometry can be a challenging topic for students. Essentially, at its heart, it is about conversions using fractions which are unlikely a favorite subject in math class. Sometimes, the best way to help students understand stoichiometry is to show them how it works in the common experiment of vinegar and baking soda.

#### Materials

• 2 beakers at least 100 mL
• Baking Soda (NaHCO3)
• Vinegar (CH3COOH)
• digital scale capable of measuring in grams
• grease pencils
• stirring rode

#### Procedures

1. Explain to students that today you are going to prove to them that stoichiometry is true, all using baking soda and vinegar.
2. Have students label one beaker 'A' and the other 'B'.
3. Students should place beaker A on the balance and accurately record its mass to the hundredths place.
4. Without removing the beaker from the scale, have students add about 10 grams of baking soda to the beaker. It doesn't have to be exactly 10 grams, as long as the mass of the beaker plus the baking soda is recorded accurately.
5. Students should set beaker A aside, and place beaker B on the scale. Record its mass to the hundredths place.
6. Next, students should add 50 grams of vinegar to beaker B. Again, it doesn't have to be exactly 50 as long as an accurate mass is recorded.
7. Have students slowly add the vinegar to the baking soda, stirring carefully until bubbles of CO2 stop forming.
8. Have students measure the mass of beaker A and beaker B again.
9. To calculate the mass of vinegar used, students should subtract the mass of beaker B after from beaker B before.
10. Review with students the equation for the chemical reaction of baking soda and vinegar:

1. Have students use stoichiometry to calculate that should be remaining in beaker A of water and sodium acetate.
2. Students should begin the stoichiometry with the mass of the baking soda used in the experiment. They can then convert it to moles by using the total mass of 1 mole of baking soda (84 grams). That mass is calculated by adding up the atomic mass of all the elements present in baking soda in the correct ratios.

1. Since the ratio of moles of baking soda to moles of water is 1:1, the number of moles of baking soda is equal to the moles of water and sodium acetate. Students can use this 1:1 ratio to finish the calculation and determine how much sodium acetate and water were left in the beaker. This will give them their theoretical yield.
2. Students can then compare their calculations and actual data to calculate their percent error in comparing their theoretical yield to their actual yield.

### Scaffolding Stoichiometry

#### Materials

• cards with examples of balanced chemical equations (each part of the equation should be labeled A, B, C ….)
• cards with directions (such as 'Convert moles of reactant A to product B).
• laminated index cards labeled with common parts of stoichiometry problems (moles, grams, etc.)
• dry erase markers

#### Procedures

1. Have students work in small groups.
2. Students should randomly draw a chemical equation card and a directions card.
3. Using the chemical equation and directions, have students use the labeled cards to map out the conversion required by the directions.
4. They can repeat this process over and over, drawing different combinations of equations and directions cards.
5. If you want, you can even turn it into a game. Set up a simple race track on your dry erase board, and give each team a marker. When each team completes one problem successfully, they can advance on the board. The first team to cross the finish line wins!

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