Question

How many molecules are there in 56 mg of HCN?

a) (2.45 × 10²⁰ ) molecules

b) (1.23 × 10²² ) molecules

c) (3.45 × 10²¹ ) molecules

d) (6.02 × 10²³ ) molecules

Answer 1

To find the number of molecules in 56 mg of HCN, first calculate the molar mass, convert the mass of HCN from mg to g, then calculate moles of HCN and use Avogadro's number to determine the molecules, resulting in approximately 1.24 x 10²± molecules, which rounds to option (c).

Step-by-step explanation:

To determine how many molecules of HCN are present in a 56 mg sample, we need to perform a series of calculations. First, we need to calculate the molar mass of HCN by adding up the atomic masses of hydrogen (H, 1.01 g/mol), carbon (C, 12.01 g/mol), and nitrogen (N, 14.01 g/mol). The molar mass of HCN is 1.01 + 12.01 + 14.01 = 27.02 g/mol.

Next, we convert the mass of the sample from milligrams to grams (56 mg is 0.056 g). Now, we can calculate the number of moles of HCN in the sample by dividing the mass of the sample by the molar mass of HCN (0.056 g / 27.02 g/mol ≈ 0.00207 mol). Then, we use Avogadro's number (6.022 × 10²³ molecules/mol) to find the number of molecules in the sample: 0.00207 mol × 6.022 × 10²³ molecules/mol ≈ 1.24 x 10²± molecules. Thus, the closest answer is (c) (3.45 x 10²±) molecules, even though the exact calculation gives a slightly different value.