Question

1. how many particles are in 1.20 mol of sodium sulfide?
2. how many particles are in 1.25 mol of no₂?
3. a small pin contains 0.0178 mol of iron, fe. how many atoms of iron are in the pin?
4. how many formula units are in 0.21 mol of magnesium nitrate, mg(no₃)₂?
5. a litre of water contains 55.6 mol of water. how many molecules of water are in this sample?
6. ethyl acetate, c₄h₈o₂, is frequently used in nail polish remover. a typical bottle of nail polish remover contains about 2.5 mol of ethyl acetate. how many molecules are in the bottle of nail polish remover?

Explanation:

Step1: Recall Avogadro's number

Avogadro's number ($N_A$) is $6.022\times 10^{23}$ particles/mol.

Step2: Use the formula $N = n\times N_A$ for each part

• Question 4:
• Given $n = 1.20$ mol of sodium sulfide ($Na_2S$).
• $N=1.20\ mol\times6.022\times 10^{23}\ particles/mol = 7.2264\times 10^{23}$ particles.
• Question 5:
• Given $n = 1.25$ mol of $NO_2$.
• $N = 1.25\ mol\times6.022\times 10^{23}\ particles/mol=7.5275\times 10^{23}$ particles.
• Question 6:
• Given $n = 0.0178$ mol of iron ($Fe$).
• $N=0.0178\ mol\times6.022\times 10^{23}\ atoms/mol = 1.071916\times 10^{22}$ atoms.
• Question 7:
• Given $n = 0.21$ mol of magnesium nitrate ($Mg(NO_3)_2$).
• $N = 0.21\ mol\times6.022\times 10^{23}\ formula - units/mol=1.26462\times 10^{23}$ formula - units.
• Question 8:
• Given $n = 55.6$ mol of water ($H_2O$).
• $N = 55.6\ mol\times6.022\times 10^{23}\ molecules/mol = 3.348232\times 10^{25}$ molecules.
• Question 9:
• Given $n = 2.5$ mol of ethyl acetate ($C_4H_8O_2$).
• $N=2.5\ mol\times6.022\times 10^{23}\ molecules/mol = 1.5055\times 10^{24}$ molecules.

Answer:

1. $7.23\times 10^{23}$ particles
2. $7.53\times 10^{23}$ particles
3. $1.07\times 10^{22}$ atoms
4. $1.26\times 10^{23}$ formula - units
5. $3.35\times 10^{25}$ molecules
6. $1.51\times 10^{24}$ molecules