How many atoms are there in a 15.0-g sample of KBr?
mol KBr = grams/molar mass
Then molecules KBr = mols x 6.022E23
Then twice that will be the number of atoms since there are two atoms per mol KBr.
To find the number of atoms in a given sample of a substance, we need to use the concept of molar mass and Avogadro's number.
Step 1: Determine the molar mass of KBr.
K (potassium) has a molar mass of 39.10 g/mol.
Br (bromine) has a molar mass of 79.90 g/mol.
Adding the molar masses of potassium and bromine:
Mass of KBr = 39.10 g/mol + 79.90 g/mol = 119.00 g/mol
Step 2: Calculate the number of moles.
Number of moles = Mass of sample / Molar mass
Number of moles = 15.0 g / 119.00 g/mol ≈ 0.126 moles
Step 3: Use Avogadro's number to convert moles to atoms.
1 mole of any substance contains 6.022 x 10^23 representative particles, which is Avogadro's number.
Number of atoms = Number of moles x Avogadro's number
Number of atoms = 0.126 moles x 6.022 x 10^23 atoms/mole
Now, let's calculate the number of atoms:
Number of atoms ≈ 7.59 x 10^22 atoms
Therefore, there are approximately 7.59 x 10^22 atoms in a 15.0-g sample of KBr.