Stoichiometry with Mass: Stoichiometry Tutorial Part 2

Summary

This video tutorial teaches how to solve stoichiometry problems involving mass, using both practical examples and chemical reactions. The process includes converting between mass and moles, with clear steps: writing the balanced equation, calculating molar masses, and using conversion factors. The video demonstrates this with a real-world example of ordering hot dog buns based on available hot dog meat and a chemical example involving the electrolysis of water. The tutorial emphasizes the importance of practicing stoichiometry for mastery, helping viewers build confidence in solving similar problems.

Takeaways

• 😀 Stoichiometry problems involving mass require converting mass to moles, then from moles of one substance to another, and finally back to mass.
• 😀 To solve stoichiometry problems, it is essential to work with moles, as this is the standard unit for chemical conversions.
• 😀 A practical example of stoichiometry is ordering ingredients in a restaurant, like converting pounds of hot dog meat to pounds of buns.
• 😀 In the restaurant example, first calculate the number of hot dogs by converting the weight of hot dog meat (pounds) to hot dogs (by using the weight of a single hot dog).
• 😀 After calculating the number of hot dogs, use the balanced reaction (1 hot dog = 1 bun) to determine the number of buns required.
• 😀 Convert the number of buns to pounds by multiplying by the mass of a single bun (0.1 pounds).
• 😀 For chemical stoichiometry, write down the balanced reaction, like the electrolysis of water (H2O → H2 + O2), before proceeding with the calculations.
• 😀 Molar masses must be calculated to convert between mass and moles, e.g., water’s molar mass is 18.02 grams per mole, and oxygen’s molar mass is 32 grams per mole.
• 😀 The conversion of mass to moles involves dividing the given mass by the molar mass of the substance.
• 😀 After converting to moles, apply the stoichiometric ratios from the balanced equation to convert moles of one substance to moles of another.
• 😀 Finally, convert the resulting moles back into mass by multiplying by the molar mass of the desired substance (e.g., oxygen).

Q & A

What are the three steps involved in solving stoichiometry problems that involve mass?

The three steps are: 1) Convert mass to moles, 2) Convert from moles of one chemical to moles of another, and 3) Convert moles back to mass if necessary.

Why is it necessary to convert mass to moles when solving stoichiometry problems?

It is necessary because stoichiometry calculations rely on the relationship between moles of different chemicals. Moles are the standard unit of measurement in chemical reactions, and they allow for proper conversion between substances.

In the example with hot dog meat and buns, what balanced equation is used?

The balanced equation used is: 1 hot dog and 1 bun make 1 hot dog with bun.

How do you calculate the number of hot dogs from 11 pounds of hot dog meat?

To calculate the number of hot dogs, you divide 11 pounds by the weight of one hot dog (0.125 pounds). This gives 88 hot dogs.

What is the conversion factor used to convert the number of hot dogs to the number of buns?

The conversion factor is based on the balanced reaction: 1 hot dog requires 1 bun. Therefore, the number of hot dogs directly gives the number of buns needed.

What mass of buns is required for 88 hot dogs?

To calculate the mass of buns, you multiply the number of buns (88) by the mass of one bun (0.1 pounds). This gives 8.8 pounds of buns.

In the electrolysis of water example, what is the first step to solve the stoichiometry problem?

The first step is to write down the balanced chemical equation for the reaction: 2H2O → 2H2 + O2.

Why is it important to balance the equation in the electrolysis of water problem?

Balancing the equation ensures the correct mole ratios between the reactants and products, which is essential for accurate stoichiometric calculations.

What is the molar mass of water, and how is it calculated?

The molar mass of water is calculated by adding the molar masses of hydrogen and oxygen. Since water has two hydrogen atoms (2 × 1.008) and one oxygen atom (16), the total molar mass is 18.02 grams per mole.

How do you convert 100 grams of water to moles?

To convert grams of water to moles, divide the mass by the molar mass of water. For 100 grams, divide 100 by 18.02, which gives 5.55 moles of water.

How do you use the mole ratio to convert moles of water to moles of oxygen in the electrolysis of water?

Using the balanced equation, 2 moles of water produce 1 mole of oxygen. To convert moles of water to moles of oxygen, multiply the moles of water (5.55) by the ratio (1 O2 / 2 H2O), which gives 2.775 moles of oxygen.

What is the final step in the stoichiometry problem involving the electrolysis of water?

The final step is to convert moles of oxygen (2.775 moles) to grams. Multiply by the molar mass of oxygen (32 grams per mole) to get the mass of oxygen: 2.775 × 32 = 88.8 grams of oxygen.