Question

10)one drop of water weighs 0.040 g. how many molecules are there in one drop, taking the gram formula mass (molar mass) of water to be 18 g/mol? 11)isopentyl acetate, c₇h₁₄o₂, the compound responsible for the scent of bananas, can be produced commercially. interestingly, some bees release about 1 μg (1 x 10⁻⁶ g) of this compound when they sting. it is believed the resulting scent attracts other bees to join the attack. how many molecules of isopentyl acetate are released in a typical bee sting? 12)how many moles are there in 303 g of potassium nitrate? how many molecules are there? 13)a silicon chip used in an integrated circuit of a microcomputer has a mass of 0.006 g. how many silicon (si) atoms are present in the chip?

Explanation:

Step1: Recall mole - mass relationship

The number of moles $n$ is calculated by the formula $n=\frac{m}{M}$, where $m$ is the mass and $M$ is the molar mass. And the number of molecules/atoms $N = n\times N_A$, where $N_A=6.022\times 10^{23}\text{ mol}^{- 1}$ is Avogadro's number.

10) For water ($H_2O$)

The molar mass of water $M = 18\text{ g/mol}$, and the mass of one - drop of water $m = 0.040\text{ g}$.
First, calculate the number of moles of water:
$n=\frac{m}{M}=\frac{0.040\text{ g}}{18\text{ g/mol}}\approx0.00222\text{ mol}$
Then, calculate the number of water molecules:
$N=n\times N_A=0.00222\text{ mol}\times6.022\times 10^{23}\text{ mol}^{-1}\approx1.33\times 10^{21}$ molecules

11) For isopentyl acetate ($C_7H_{14}O_2$)

The molar mass of $C_7H_{14}O_2$ is $M=(7\times12 + 14\times1+2\times16)\text{ g/mol}=(84 + 14+32)\text{ g/mol}=130\text{ g/mol}$. The mass $m = 1\times10^{-6}\text{ g}$.
First, calculate the number of moles:
$n=\frac{m}{M}=\frac{1\times 10^{-6}\text{ g}}{130\text{ g/mol}}\approx7.69\times 10^{-9}\text{ mol}$
Then, calculate the number of molecules:
$N=n\times N_A=7.69\times 10^{-9}\text{ mol}\times6.022\times 10^{23}\text{ mol}^{-1}\approx4.63\times 10^{15}$ molecules

12) For potassium nitrate ($KNO_3$)

The molar mass of $KNO_3$ is $M=(39 + 14+3\times16)\text{ g/mol}=(39 + 14 + 48)\text{ g/mol}=101\text{ g/mol}$. The mass $m = 303\text{ g}$.
First, calculate the number of moles:
$n=\frac{m}{M}=\frac{303\text{ g}}{101\text{ g/mol}} = 3\text{ mol}$
Then, calculate the number of molecules:
$N=n\times N_A=3\text{ mol}\times6.022\times 10^{23}\text{ mol}^{-1}=1.8066\times 10^{24}$ molecules

13) For silicon ($Si$)

The molar mass of $Si$ is $M = 28\text{ g/mol}$. The mass of the silicon chip $m=0.006\text{ g}$.
First, calculate the number of moles:
$n=\frac{m}{M}=\frac{0.006\text{ g}}{28\text{ g/mol}}\approx2.14\times 10^{-4}\text{ mol}$
Then, calculate the number of silicon atoms:
$N=n\times N_A=2.14\times 10^{-4}\text{ mol}\times6.022\times 10^{23}\text{ mol}^{-1}\approx1.29\times 10^{20}$ atoms

Answer:

1. Approximately $1.33\times 10^{21}$ molecules
2. Approximately $4.63\times 10^{15}$ molecules
3. 3 moles, approximately $1.8066\times 10^{24}$ molecules
4. Approximately $1.29\times 10^{20}$ atoms