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Answer 1

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Answer 2

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i.) 32g Oxygen


==> Given;. Mass of Oxygen = 32g

To find : Number of molecules in 32g of oxygen.


Ans==> Atomic mass of Oxygen (O) = 16


Molecular mass of Oxygen (O2) = 16 x 2 = 32


According to the formula,

Number of moles in the given O2(n)

$= \frac{mass \: of \: o2 \: in \: grams}{molecular \: mass \: of \: o2} \\ \\ = \frac{32}{32} = 1 \\ \\ n = 1 \: mol$

$1 \: mol \: of \: o2 \: \: contains \: 6.022 \times 10 {}^{23} molecules \ \\ that \: is \: 32 \: g \: of \: o2 \: contains \: 6.022 \times 10 {}^{23} molecules \ \\ of \: o2. \\ \\ 32g \: of \: oxygen \ : contain \ \\ : 6.022 \times 10 {}^{23} \: molecules \: of \: oxygen.$


ii.) 90g water


==> Given : Mass of water (H2O) = 90g.

To find: Number of molecules in 90g of water.


Ans==> Molecular mass of (H2O)


= (Atomic mass of H) x 2 + (Atomic mass of O) x 1

Molecular mass of H2O = 1 x 2 + 6

Molecular mass of H2O = 18


According to the formula,

Number of moles in the given H2O(n)

$= \frac{mass \: of \: h2o \: in \: grams}{molecular \: mass \: of \: h2o} \\ \\ = \frac{90}{18} = 5 \\ \\ n = 5 \: mol$
$1 \: mol \: of \: h2o \: contains \: 6.022 \times 10 {}^{23} molecules \:$
$5 \: mol \: of \: h2o \: contain \: 5 \times 6.022 \times 10 {}^{23} molecules$
$= 30.11 \times 10 {}^{23} molecules$
$that \: is \: 90g \: of \: h2o \: contains \ \\ : 30.11 \times 10 {}^{23} molecules \: of \: h2o$
$90g \: of \: water \: contains \\ 30.11 \times 10 {}^{23} molecules \: of \: water$


iii.) 8.8g carbon dioxide


==> Given: Mass of carbon dioxide (CO2)=8.8g of carbon dioxide

To Find: Number of molecules in 8.8g of carbon dioxide.


Ans==> Molecular mass of (CO2)

=(Atomic mass of C) x 1 + (Atomic mass of O) x 2

Molecular mass of CO2 = 12 x 1 +16 x 2

= 12 + 32

Molecular mass of CO2 = 44

According to the formula

Number of moles in the given CO2+(n)


$= \frac{mass \: of \: co2 \: in \: grams}{molecular \: mass \: of \: co2} \\ \\ = \frac{8.8}{44} \\ \\ = 0.2 \\ \\ n \: = 0.2 \: mol$
$1 \: mol \: of \: co2 \: contains \ \\ 6.022 \times 10 {}^{23} molecules \: \\ \\ 0.2 \: mol \: of \: co2 \: contains \: 0.2 \times 6.022 \times 10 {}^{23} \\ molecules \\ = 1.2044 \times 10 {}^{23} molecules \\ \\ that \: is \: 8.8g \: of \: co2 \: contains \: \\ 1.2044 \times 10 {}^{23} molecules \: of \: co2 \\ \\ 8.8g \: of \: co2 \: contains \: 1.2044 \times 10 {}^{23} \\ molecules \: of \: co2.$


iv.) 7.1 g chlorine

==> Given :. Mass of chlorine (Cl2) = 7.1g

To Find : Number of molecules in 7.1g of chlorine.


Ans==> Atomic mass of (Cl) 35.5

Molecular mass of chlorine (Cl2) = 35.5x2

= 71

According to the formula,

Number of moles in the given Cl2(n)

$= \frac{mass \: of \: cl2 \: in \: grams}{molecular \: mass \: of \: cl2} \\ \\ = \frac{7.1}{7.1} \\ \\ = 0.1 \\ n \: = 0.1 \: mol$
$1 \: mol \: of \: cl2 \: contains \: 6.022 \times 10 {}^{23} \\ molecules \\ \\0. 1 \: mol \: of \: cl2 \: contains \: 0.1 \times 6.022 \times 10 {}^{23} \\ molecules \\ = 0.6022 \times 10 {}^{23} molecules \\ \\ that \: is \: 7.1g \: of \: cl2 \: contains \\ 0.6022 \times 10 {}^{23} molecules \: \\ of \: cl2 \\ \\ 7.1g \: of \: cl2 \: contains \: 0.6022 \times 10 {}^{23} \\ molecules \: of \: chlorine.$


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