EDUCA PE| ENSINO MÉDIO | QUÍMICA | 1º ANO I QUANTIDADES EM QUÍMICA I PARTE 2

Summary

In this chemistry lesson, Professor Emanuel Marisco covers key topics related to molecular mass and volume calculations. He explains how to determine molecular mass by summing the atomic masses of elements in a compound and introduces the concept of molecular grams (moles) and the importance of Avogadro's number. The video also explores volume calculations for gases under standard conditions (CNT) and standard temperature and pressure (CPT). Through various examples, he demonstrates how to calculate these values with real-world applications, making the concepts easy to understand. The video aims to help students master these essential chemical calculations.

Takeaways

• 😀 The molecular mass is calculated by summing the product of the number of atoms and their respective atomic mass.
• 😀 The molecular mass indicates how many times a molecule is heavier than one twelfth of the mass of carbon-12.
• 😀 To calculate molecular mass, you multiply the number of atoms of each element by its atomic mass and then sum the products.
• 😀 Example 1: The molecular mass of water (H2O) is 18 units (2×1 for hydrogen and 1×16 for oxygen).
• 😀 Example 2: The molecular mass of ethyl alcohol (C2H6) is 46 units (2×12 for carbon, 6×1 for hydrogen, and 1×16 for oxygen).
• 😀 Molecular mass calculation follows the same principle for larger compounds, such as aluminum sulfate, which has a molecular mass of 342 units.
• 😀 A molecule-gram (mol) is numerically equal to the molecular mass but expressed in grams, representing a mole of molecules.
• 😀 One mole of particles corresponds to 6.02 × 10^23 particles, known as Avogadro's number.
• 😀 To calculate the number of molecules in a given mass, divide the mass of the substance by the molar mass and multiply by Avogadro's number.
• 😀 The volume of one mole of a gas at standard temperature and pressure (STP) is 22.4 liters (for CNTP) and 22.7 liters (for CPTP).
• 😀 Example 3: 8.8 grams of propane (C3H8) at CNTP occupies 4.48 liters, calculated using a straightforward ratio based on molar volume.
• 😀 Gas volume can also be calculated through the mole concept by applying a simple rule of three, using the volume of one mole at STP.

Q & A

What is molecular mass and how is it calculated?

Molecular mass is calculated by summing the product of the number of atoms (index) and the respective atomic mass of each element in a molecule. It represents how many times the mass of a molecule is heavier than one twelfth of the mass of carbon-12.

How do you calculate the molecular mass of water (H2O)?

To calculate the molecular mass of water, you multiply the number of hydrogen atoms (2) by the atomic mass of hydrogen (1) and the number of oxygen atoms (1) by the atomic mass of oxygen (16). The calculation is: (2 × 1) + (1 × 16) = 18 units.

What is the molecular mass of ethyl alcohol (C2H6O)?

To calculate the molecular mass of ethyl alcohol, you multiply the number of carbon atoms (2) by the atomic mass of carbon (12), the number of hydrogen atoms (6) by the atomic mass of hydrogen (1), and the number of oxygen atoms (1) by the atomic mass of oxygen (16). The calculation is: (2 × 12) + (6 × 1) + (1 × 16) = 46 units.

What is the difference between 'molecular gram' and 'atomic gram'?

'Molecular gram' (molar mass) is numerically equal to molecular mass but expressed in grams, whereas 'atomic gram' is the mass of one mole of atoms. Both are based on the number of particles (atoms or molecules) in one mole, which is Avogadro’s number (6.02 x 10^23).

How do you calculate the number of molecules in a given mass of a substance?

To calculate the number of molecules, you first find the molecular mass (in grams) of the substance. Then, use a rule of three to find the number of molecules in the given mass, knowing that one mole corresponds to 6.02 x 10^23 molecules.

What is the molecular mass of glucose (C6H12O6)?

To calculate the molecular mass of glucose, multiply the number of carbon atoms (6) by the atomic mass of carbon (12), the number of hydrogen atoms (12) by the atomic mass of hydrogen (1), and the number of oxygen atoms (6) by the atomic mass of oxygen (16). The calculation is: (6 × 12) + (12 × 1) + (6 × 16) = 180 units.

How do you calculate the mass of molecules in a specific volume of gas at STP?

To calculate the mass of molecules in a specific volume of gas, use the molar volume at STP (22.4 liters per mole for gases). Use a rule of three where 22.4 liters of gas corresponds to 1 mole, and then find the mass of the substance in the given volume.

What is the volume of propane gas (C3H8) in 8.8 grams at STP?

First, calculate the molar mass of propane (C3H8), which is 44 g/mol. Then, use the molar volume at STP (22.4 liters) to find the volume. Using a rule of three, (8.8 g / 44 g/mol) × 22.4 L = 4.48 liters of propane gas.

How do you calculate the volume of hydrogen sulfide gas (H2S) at STP?

To calculate the volume of hydrogen sulfide (H2S) at STP, first calculate its molar mass (H = 1, S = 32), which gives a molar mass of 34 g/mol. Then, use the molar volume at STP (22.4 liters) and the given mass (e.g., 4.54 liters) to calculate the volume.

How do you determine the total volume of a gas mixture at STP?

To find the total volume of a gas mixture at STP, calculate the individual volumes of each gas based on its mass or molecular quantity, and then add them together. For example, if you have 4.48 liters of CO2 and 33.6 liters of F2, the total volume would be 38.08 liters.