Question

determine the number of molecules in a drop of water which weighs 0.09 gram

Answer 1

A mole of water(H2O) weighs (16+2)=18 gms and thus it has 6. 022 ×10^23 molecules. No. of moles in 0.09 gms of water(H2O)=0.09/18= 0.005 . It has 5×10^-3×6.022×10^23 =31.011×10^20=3.1011×10^20 molecules of water(H2O) . Hope it helps you...

Answer 2

Answer:

The number of molecules in a drop of water is  3.011 × $10^{21}$

Explanation:

Given: Weight of water is 0.09 gram

To find: The number of molecules  present in a 0.09 gram of water

Solution:

Mole:

The amount of substance that contains the same number of entities is known as a "mole."

One mole of any substance is equal to the Avogadro number. This number as value 6.023 × $10^{23}$

It is useful to measure the products in any chemical reaction

Given mass of $H_{2} O$ = 0.09

The molar mass of $H_{2} O$ = 18g

Mole = $\frac{given mass}{molar mass}$

       = $\frac{0.09}{18}$

       = 0.005 mole

Mole = $\frac{No of molecules}{Avogadro number}$

Number of molecules = Number of moles × Avogardo's Number

Number of molecules = 0.005 × 6.022 × $10^{23}$

Number of molecules of $H_{2} O$ = 3.011 × $10^{21}$

Final answer:

The number of molecules in a drop of water is  3.011 × $10^{21}$

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