Calculation of Number of Molecules of Water in a Drop of Water Weighing 0.09 gm

Introduction:
Before we start with the calculation of the number of molecules of water in a drop of water weighing 0.09 gm, let us first understand what is a molecule and what is a drop of water.

What is a molecule?
A molecule is the smallest particle of a substance that retains all the properties of that substance. It is made up of two or more atoms that are chemically bonded together.

What is a drop of water?
A drop of water is a small, spherical shaped quantity of liquid that is held together by surface tension. It is commonly measured in terms of volume or weight.

Formula:
The formula to calculate the number of molecules in a given substance is as follows:

Number of molecules = (Weight in grams / Molecular weight) x Avogadro's number

Calculation:
Now, let us use the above formula to calculate the number of molecules of water in a drop of water weighing 0.09 gm.

Step 1: Find the molecular weight of water
The molecular weight of water is 18.01528 g/mol

Step 2: Find the number of moles of water in 0.09 gm of water
Number of moles = Weight in grams / Molecular weight
Number of moles = 0.09 / 18.01528
Number of moles = 0.004996 mol

Step 3: Find the number of molecules of water in 0.004996 mol of water
Number of molecules = Number of moles x Avogadro's number
Number of molecules = 0.004996 x 6.022 x 10^23
Number of molecules = 3.011 x 10^21

Therefore, the number of molecules of water in a drop of water weighing 0.09 gm is 3.011 x 10^21.

Conclusion:
In conclusion, the weight of a drop of water is not enough to measure the number of molecules of water present in it. We need to calculate the number of moles of water in the given quantity of water and then use Avogadro's number to calculate the number of molecules of water present in it.

Given mass=0.09gm
molecular mass of water = 18gm
no. of molecules in one mole of water = 6.022×10^23
no. of molecules in 0.09gm = 0.09/18 × 6.022×10^23
= 30.11×10^20