Question

Number of molecules in one dm3 of water ??

Answer 1

Answer:

Explanation:the litre of water has 1000 grams.The number of moles=1000/18=55.556moles.

Therefore the number of molecules is close to 3.346*10²⁵ molecules(1dm³ and 1 kilogram are very close,due to the density of water being close to unity).

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Answer 2

Given: Volume of water = 1 dm³

To Find: Number of molecules in one dm³ of water

Solution:

Formulas used:

• 1 dm³ = 1L = 1000cm³
• Density of water = 1g/cm³
• Density of water - d = given mass (m)/ Volume(V)  
• number of moles(n) = given mass(m)/ molecular mass(M)
• number of molecules(N) = n × Nₐ (Nₐ = Avagadro number = 6.023 × 10²³ molecules)

Applying the above formulas:

d = m /V (Density formula)

1g/cm³ = m/1000cm³

m = 1 × 1000 = 1000g

Applying formula for calculating number of moles - n

n = m/M ( M - molecular mass of water- H₂O = 16 + 2 = 18g)

n = 1000/18

n = 55.6 moles

Applying the formula for calculating the number of molecules in 55.6 moles of water

N = n × Nₐ

N = 55.6 × 6.023 × 10²³

N = 334.88 × 10²³

N = 3.3 × 10²⁵ molecules

Hence, 3.3 × 10²⁵ molecules are present in one dm³ of water.