Question

A sample of CH4 weighs 3.423 g. How many molecules of CH4 are in the sample writing in scientific notation?

Answer 1

1.285 x 10²³ molecules CH₄

Step-by-step explanation:

To find the amount of molecules in the sample, you need to (1) convert grams to moles (using the molar mass of CH₄) and then (2) convert moles to molecules (using Avogadro's Number). It is important to arrange the ratios/conversions in a way that allows for the cancellation of units (the desired unit should be in the numerator). The final answer should have 4 sig figs like the given value (3.423 = 4 sig figs).

Atomic Mass (C): 12.011 g/mol

Atomic Mass (H): 1.008 g/mol

Molar Mass (CH₄): 12.011 g/mol + 4(1.008 g/mol)

Molar Mass (CH₄): 16.043 g/mol

Avogadro's Number:

6.022 x 10²³ molecules = 1 mole

3.423 g CH₄ 1 mole 6.022 x 10²³ molecules
----------------------- x ------------------- x ------------------------------------------- =
16.043 g 1 mole

= 1.285 x 10²³ molecules CH₄