Question

1 mole = 6.02 × 10²³ particles (atoms, molecules or formula units)
1 mole = molar mass in grams (calculate from the periodic table)
1 mole = 22.4 l (only true for gases at stp)

use the space given for each problem to show your work for possible partial credit.

______9. how many molecules are in 5.17 mol o₂?
a. 3.11 × 10²⁴ molecules c. 3.49 × 10²⁴ molecules
b. 3.79 × 10²⁴ molecules d. 1.26 × 10²⁴ molecules

______10. what is the mass in grams of 3.405 mol c₈h₁₈?
a. 0.0512 g c. 389 g
b. 19.4 g d. 673 g

______11. what is the number of moles in 6.63 l of h₂s gas at stp?
a. 0.296 mol c. 3.54 mol
b. 0.430 mol d. 148 mol

______12. find the number of moles in 25 grams of cacl₂.
a) 0.351 moles b) 13875 moles c) 1.126 moles d) 0.225 moles

______13. how many molecules are in 11.45 g of n₂o?
a. 6.89 × 10²⁴ molecules c. 1.98 × 10²² molecules
b. 5.26 × 10²² molecules d. 1.57 × 10²³ molecules

______14. what is the mass in grams of 3.45 l of so₂ gas at stp?
a) 2.04 × 10²⁴ grams b) 217.36 grams c) 9.867 grams d) 64.064 grams

______15. what is the volume in liters of 3.359 × 10²⁵ atoms of neon gas at stp?
a) 501.76 l b) 28018 l c) 1250 l d) 25241 l

Explanation:

Step1: Use Avogadro's number

The formula to find the number of molecules is \(N = n\times N_{A}\), where \(n\) is the number of moles and \(N_{A}=6.02\times 10^{23}\) molecules/mol.
Given \(n = 5.17\) mol of \(O_{2}\), then \(N=5.17\times6.02\times 10^{23}\)

Step2: Calculate the value

\(5.17\times6.02 = 31.1234\)
So \(N = 31.1234\times 10^{23}=3.11234\times 10^{24}\approx3.11\times 10^{24}\) molecules

Answer:

a. \(3.11\times 10^{24}\) molecules