Question

1. how many formula units are in 0.21 mol of magnesium nitrate, mg(no₃)₂?

n=
n=
n_a=

1. a litre of water contains 55.6 mol of water. how many molecules of water are in this sample?
2. 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 the formula

The formula to calculate the number of formula units/molecules (\(N\)) is \(N = n\times N_{A}\), where \(n\) is the number of moles and \(N_{A}=6.022\times 10^{23}\space mol^{- 1}\) (Avogadro's number).

Step2: Solve for problem 7

Given \(n = 0.21\space mol\) of \(Mg(NO_{3})_{2}\).
Substitute into the formula: \(N=0.21\space mol\times6.022\times 10^{23}\space mol^{-1}\)
\(N = 1.26462\times 10^{23}\approx1.3\times 10^{23}\) formula units.

Step3: Solve for problem 8

Given \(n = 55.6\space mol\) of \(H_{2}O\).
Substitute into the formula: \(N = 55.6\space mol\times6.022\times 10^{23}\space mol^{-1}\)
\(N=55.6\times6.022\times 10^{23}=3.358232\times 10^{25}\approx3.36\times 10^{25}\) molecules.

Step4: Solve for problem 9

Given \(n = 2.5\space mol\) of \(C_{4}H_{8}O_{2}\).
Substitute into the formula: \(N=2.5\space mol\times6.022\times 10^{23}\space mol^{-1}\)
\(N = 1.5055\times 10^{24}\approx1.5\times 10^{24}\) molecules.

Answer:

1. \(1.3\times 10^{23}\) formula units.
2. \(3.36\times 10^{25}\) molecules.
3. \(1.5\times 10^{24}\) molecules.