Question

Calculate the number of moles in 35.7 g of CH4

Answer 1

There are 2.2 moles in 35.7 g of CH4! To find this, you have to divide 35.7 by the molar mass of CH4, which is 16.0!

Answer 2

Answer:

$\boxed {\boxed {\sf About \ 2.23 \ moles \ CH_4}}$

Explanation:

First, find the molar mass of CH₄

This compound is made of carbon (C) and hydrogen (H). Look on the Peirodic Table for the masses of both elements.

• Carbon: 12.011 g/mol
• Hydrogen: 1.008 g/mol

Now, count the number of moles in the compound. There is no subscript on C, indicating 1 mole. There is a subscript of 4 on H, indicating 4 moles. We must multiply the molar mass of hydrogen by 4.

• 1 Carbon: 12.011 g/mol
• 4 Hydrogen: (4 * 1.008 g/mol)= 4.032 g/mol

Add the 2 masses.

• 12.011 g/mol + 4.032 g/mol = 16.043 g/mol

Next, find the number of moles in 35.7 grams.

Use the molar mass of CH₄ as a ratio.

$\frac{16.043 \ g \ CH_4}{1 \ mol \ CH_4}$

Since we want the units of grams CH₄ to cancel when we multiply, we must flip the ratio.

$\frac{1 \ mol \ CH_4}{16.043 \ g \ CH_4}$

Multiply by 35.7 grams.

$35.7 \ g \ CH_4 *\frac{1 \ mol \ CH_4}{16.043 \ g \ CH_4}$

The grams of CH₄ will cancel each other out.  Since there is a 1 in the numerator, we can also move 35.7 to the numerator.

$35.7 *\frac{1 \ mol \ CH_4}{16.043 }$

$\frac{35.7 \ mol \ CH_4}{16.043}$

$2.22526959 \ mol \ CH_4$

The original measurement given, 35.7 grams, has 3 significant figures (3, 5, and 7), so we must round to 3 sig figs.

For this number, it is the hundredth place.

The 5 in the thousandth place tells us to round the 2 to a 3.

$2.23 \ mol \ CH_4$

There are about 2.23 moles of CH₄ in 35.7 grams.