How to Find the Percent Composition by Mass for Zn(OH)2 (Zinc hydroxide)

Summary

This video explains how to calculate the percent composition by mass for each element in zinc hydroxide (Zn(OH)2). First, the molar mass of the compound is determined as 99.39 grams per mole. The percent composition of each element (zinc, oxygen, and hydrogen) is calculated by dividing the molar mass of the individual element by the total molar mass, then multiplying by 100. The results are 66.77% for zinc, 32.20% for oxygen, and 2.03% for hydrogen. The sum of these percentages gives a total close to 100%.

Takeaways

• 🧪 The goal is to find the percent composition by mass for each element in zinc hydroxide (Zn(OH)2).
• 📊 The first step is calculating the molar mass of zinc hydroxide, which is 99.39 grams per mole.
• ⚖️ The molar mass of each element is used to calculate the percent composition of that element in the compound.
• 🧬 For zinc, the molar mass is 65.37 grams per mole, and the percent composition is calculated by dividing this by the molar mass of Zn(OH)2.
• 📉 The percent composition of zinc in zinc hydroxide is 66.77%.
• 🌬️ The atomic mass of oxygen is 16.00 grams per mole, and there are two oxygen atoms in the compound.
• 🔢 The percent composition of oxygen in Zn(OH)2 is 32.20%.
• 🔬 For hydrogen, the atomic mass is 1.008 grams per mole, and there are two hydrogen atoms.
• 📐 The percent composition of hydrogen in Zn(OH)2 is 2.03%.
• ✅ The sum of the percent compositions for all elements should add up to close to 100%, though minor rounding differences may occur.

Q & A

What is the compound discussed in the video?

The compound discussed is zinc hydroxide, with the chemical formula Zn(OH)₂.

What is the first step in calculating the percent composition by mass for each element in Zn(OH)₂?

The first step is to calculate the molar mass of Zn(OH)₂ by adding the atomic masses of all its elements.

What is the molar mass of zinc hydroxide (Zn(OH)₂)?

The molar mass of zinc hydroxide is 99.39 grams per mole.

How is the percent composition of zinc in Zn(OH)₂ calculated?

The percent composition of zinc is calculated by dividing its atomic mass (65.37 g/mol) by the molar mass of Zn(OH)₂ (99.39 g/mol), then multiplying by 100 to get 66.77%.

What is the atomic mass of oxygen used in the video?

The atomic mass of oxygen used in the video is 16.00 grams per mole.

How many oxygen atoms are present in Zn(OH)₂, and how is their percent composition calculated?

There are two oxygen atoms in Zn(OH)₂. Their percent composition is calculated by multiplying the atomic mass of oxygen (16.00 g/mol) by 2, dividing by the molar mass of Zn(OH)₂ (99.39 g/mol), and then multiplying by 100 to get 32.20%.

What is the percent composition of hydrogen in Zn(OH)₂?

The percent composition of hydrogen is calculated to be 2.03%.

How many hydrogen atoms are present in Zn(OH)₂?

There are two hydrogen atoms in Zn(OH)₂.

What should the sum of the percent compositions for all elements in Zn(OH)₂ approximately equal?

The sum of the percent compositions for all elements in Zn(OH)₂ should approximately equal 100%.

What is the general process for calculating the percent composition by mass for any element in a compound?

The general process is to divide the atomic mass of the element (multiplied by the number of atoms of that element in the compound) by the molar mass of the compound, then multiply by 100 to get the percentage.