Question

Rank the following samples in number of atoms from least to greatest. a) 1.5 mol of K atoms b) 64 g of S c) 20 g of Be d) 25 g of Na

Answer 1

To determine the number of atoms in each sample, we calculate the number of moles of each and then use this number to rank the samples since the number of moles is directly proportional to the number of atoms. The ranking from least to greatest is: 25 g of Na, 64 g of S, 1.5 mol of K, and 20 g of Be.

Step-by-step explanation:

To rank the following samples in the number of atoms from least to greatest, we need to calculate the number of moles for each and then use Avogadro's number (6.022 x 1023 atoms/mol) to find the total number of atoms.

• (a) 1.5 mol of K atoms: This sample has 1.5 moles of potassium (K) atoms.
• (b) 64 g of S: To find the number of moles, divide the mass by the molar mass of sulfur (S), which is 32.07 g/mol. Number of moles = 64 g / 32.07 g/mol = 1.996 moles.
• (c) 20 g of Be: To find the number of moles, divide the mass by the molar mass of beryllium (Be), which is 9.0122 g/mol. Number of moles = 20 g / 9.0122 g/mol = 2.220 moles.
• (d) 25 g of Na: To find the number of moles, divide the mass by the molar mass of sodium (Na), which is 22.99 g/mol. Number of moles = 25 g / 22.99 g/mol = 1.087 moles.

We can use Avogadro's number to convert the moles to atoms. However, since the moles directly relate to the number of atoms (1 mole = 6.022 x 1023 atoms), we can simply rank the samples by their number of moles, as they will be directly proportional. Here is the ranking from least to greatest number of atoms:

1. (d) 25 g of Na: 1.087 moles
2. (b) 64 g of S: 1.996 moles
3. (a) 1.5 mol of K atoms: 1.5 moles
4. (c) 20 g of Be: 2.220 moles

Answer 2

Na < K < S < Be

Step-by-step explanation:

Let's work with NA and molar mass of each.

- 1.5 mol of K → should be converted to atoms ( mol . NA)

1.5 mol . 6.02×10²³ = 9.03×10²³ atoms of K

- 64 g of S → should be converted to mol (mass / molar mass). Then, into atoms. (mol . NA)

64 g / 32.06 g/m = 1.99 mol

1.99 m . 6.02×10²³ = 1.20×10²⁴ atoms of S

- 20 g of Be → should be converted to mol (mass / molar mass). Then, into atoms. (mol . NA)

20 g / 9.01 g/m = 2.22 moles

2.22 m . 6.02×10²³ = 1.33×10²⁴ atoms of Be

- 25 g of Na → should be converted to mol (mass / molar mass). Then, into atoms. (mol . NA)

25 g / 23 g/m = 1.08 moles

1.08 m . 6.02×10²³ = 6.54×10²³ atoms of Na