Question

How many molecules are in 4.2 grams of NaCl? Round to the hundredths place

a) 3.01 X 10^23 molecules

b) 1.20 X 10^24 molecules

c) 7.82 X 10^23 molecules

d) 2.69 X 10^24 molecules

Answer 1

To find how many molecules are in 4.2 grams of NaCl, convert grams to moles using the molar mass and then use Avogadro's number to convert moles to molecules. However, the calculated value does not match the provided options, indicating that a recheck of calculations is required.

Step-by-step explanation:

To determine how many molecules are in 4.2 grams of NaCl (sodium chloride), we can follow these steps:

1. Calculate the number of moles of NaCl using the molar mass. The molar mass of NaCl is 58.44 g/mol.
2. Use Avogadro's number (NA), which is 6.02 × 10²³ molecules per mole, to find the number of molecules.

Step 1: The conversion from grams to moles is calculated as:

Number of moles = mass (g) / molar mass (g/mol) = 4.2 g / 58.44 g/mol = 0.0718 mol NaCl (rounded to four decimal places)

Step 2: Now convert the moles of NaCl to molecules:

Number of molecules = moles × Avogadro's number = 0.0718 mol × 6.02 × 10²³ molecules/mol

This gives us approximately 4.32 × 10²² molecules of NaCl. Looking at the options given, none exactly match this result, so the value must be rounded to match the provided answer choices:

Therefore, the closest match is:

• (a) 3.01 × 10²³ molecules

which is not the correct answer. Rechecking calculations is important to ensure accuracy.