Question

How many molecules are in 252.3 g H2S?

Answer 1

`\boxed {\boxed {\sf 4.457*10^(24) \ molecules \ H_2S}}`

Step-by-step explanation:

First, find the molar mass of H₂S

Use the Periodic Table to find the mass of hydrogen and sulfur.

• Hydrogen (H): 1.008 g/mol
• Sulfur (S): 32.07 g/mol

To find the molar mass of H₂S, multiply the molar mass of the elements by the number of atoms of the element.

• Hydrogen (2): (2)(1.008 g/mol) =2.016 g/mol
• Sulfur (1 atom): (1)(32.07 g/mol)= 32.07 g/mol

Add.

• 2.016 g/mol + 32.07 g/mol =34.086 g/mol

Next, find the number of moles in the sample (252.3 g) Use the ratio of grams to moles.

`252.3 / g * (1 \ mol \ H_2S)/(34.086 \ g )`

Multiply. The grams will cancel each other out.

`(252.3 / mol )/(34.086 \ )=7.40186587 \ mol`

Finally, found the number of molecules using Avogadro's number (There are 6.022*10²³ molecules in 1 mole).

`7.40186587 \ mol \ H_2S*(6.022*10^(23) molecules \ H_2S)/(1 \ mol \ H_2S)`

Multiply. The mole (mol) will cancel each other out.

`7.40186587*{6.022*10^(23)\ molecules \ H_2S} = 4.45740363 *10^(24) \ molecules \ H_2S`

Round to the correct number of significant figures. The sample had 4 sig figs (2, 5, 2, 3), so round to 4 sig figs.

`4.457*10^(24) \ molecules \ H_2S`

There are about 4.457 * 10²⁴ molecules of H₂S

Answer 2

4.457 × 10²⁴ molecules H₂S

General Formulas and Concepts:

Chemistry - Atomic Structure

• Reading a Periodic Table
• Using Dimensional Analysis
• Avogadro's Number - 6.022 × 10²³ atoms, molecules, formula units, etc.

Step-by-step explanation:

Step 1: Define

252.3 g H₂S

Step 2: Identify Conversions

Avogadro's Number

Molar Mass of H - 1.01 g/mol

Molar Mass of S - 32.07 g/mol

Molar Mass of H₂S - 2(1.01) + 32.07 = 34.09 g/mol

Step 3: Convert

`252.3 \ g \ H_2S((1 \ mol \ H_2S)/(34.09 \ g \ H_2S) )((6.022 \cdot 10^(23) \ molecules \ H_2S)/(1 \ mol \ H_2S) )` = 4.45688 × 10²⁴ molecules H₂S

Step 4: Check

We are given 4 sig figs. Follow sig fig rules and round.

4.45688 × 10²⁴ molecules H₂S ≈ 4.457 × 10²⁴ molecules H₂S