Questions: One millilitre has about 15 drops. One drop of water has 1.67 × 10^21 H2O (water) molecules. Estimate the number of molecules in 1 litre of water. Write down your answer in standard form.

Solution Steps

First, we need to convert 1 litre of water to millilitres. Since 1 litre is equal to 1000 millilitres, we have: \[ 1 \, \text{litre} = 1000 \, \text{millilitres} \]

Given that 1 millilitre has about 15 drops, we can calculate the number of drops in 1000 millilitres: \[ 1000 \, \text{millilitres} \times 15 \, \text{drops/millilitre} = 15000 \, \text{drops} \]

We know that one drop of water contains \(1.67 \times 10^{21}\) water molecules. Therefore, the number of molecules in 15000 drops is: \[ 15000 \, \text{drops} \times 1.67 \times 10^{21} \, \text{molecules/drop} \]

To find the total number of molecules, we multiply the two numbers: \[ 15000 \times 1.67 \times 10^{21} \] \[ = 1.67 \times 10^{21} \times 1.5 \times 10^{4} \] \[ = 1.67 \times 1.5 \times 10^{25} \] \[ = 2.505 \times 10^{25} \]

Final Answer