The density of water, H20(1), is 1.0 g/mL. How many atoms of oxygen are present in 2.5 L of pure water? A) 8.4 x 10^25 B) 1.4 x 10^21 C) 2.3 x 10^-22 D) 1.5 x 10^27 E) 2.7 x 10^26 The mass of 2.5 L of water is mass = dV = 1.00 g mL^-1 x 2500 mL = 2500 g Note the conversion from L to mL (1 L = 1000 mL). The amount of water is thus2500 g Moles of H_2O= m_H2O/M_H2O =2500 g/ 18.015 g mol^-1=13_8 molMultiplying by the Avogadro constant gives the number of water molecules which equals the number of oxygen atoms since there is one oxygen atom per water molecule. number of O atoms = 13_8 x 6.022×1023 atoms ml^-1 = 8.4×10^25Shouldn’t it be 2H2 + O2 -> 2H2O? but how come in the picture i’ve attached, it is 1 oxygen = 1 h2o
The Correct Answer and Explanation is :
Let’s walk through the calculation and explanation step by step, addressing the process and your question:
Given Data:
- Density of water (H₂O) = 1.0 g/mL
- Volume of water = 2.5 L = 2500 mL
- Molar mass of H₂O = 18.015 g/mol
- Avogadro’s number (NA) = 6.022 × 10²³ atoms/mol
Step 1: Calculate the Mass of Water
From the given density of water (1.0 g/mL), we can calculate the mass of the 2.5 L of water:
[
\text{Mass} = \text{Density} \times \text{Volume} = 1.0 \, \text{g/mL} \times 2500 \, \text{mL} = 2500 \, \text{g}
]
Thus, the mass of 2.5 L of water is 2500 grams.
Step 2: Calculate the Number of Moles of H₂O
Now, let’s determine how many moles of H₂O are present in 2500 grams. Using the molar mass of water (18.015 g/mol):
[
\text{Moles of H₂O} = \frac{\text{Mass of H₂O}}{\text{Molar mass of H₂O}} = \frac{2500 \, \text{g}}{18.015 \, \text{g/mol}} \approx 138.6 \, \text{mol}
]
This means there are approximately 138.6 moles of water molecules in 2.5 L of water.
Step 3: Calculate the Number of Water Molecules
Next, we use Avogadro’s number to determine the number of water molecules:
[
\text{Number of H₂O molecules} = 138.6 \, \text{mol} \times 6.022 \times 10^{23} \, \text{molecules/mol} \approx 8.36 \times 10^{25} \, \text{molecules}
]
Thus, the number of water molecules in 2.5 L of water is approximately (8.4 \times 10^{25}).
Step 4: Number of Oxygen Atoms
Since each water molecule (H₂O) contains exactly one oxygen atom, the number of oxygen atoms in the 2.5 L of water will be the same as the number of water molecules. Therefore, the number of oxygen atoms is also:
[
\text{Number of oxygen atoms} = 8.4 \times 10^{25}
]
Answer:
The correct answer is A) (8.4 \times 10^{25}) oxygen atoms.
Why Is It 1 Oxygen Atom per Water Molecule?
In the structure of a water molecule (H₂O), there is one oxygen atom bonded to two hydrogen atoms. The balanced chemical equation for the formation of water from hydrogen and oxygen (2H₂ + O₂ → 2H₂O) shows that one molecule of O₂ is required to form two water molecules. However, each individual water molecule (H₂O) contains exactly one oxygen atom, not two. So, despite oxygen being involved in the reaction with hydrogen to form water, each H₂O molecule still contains only one oxygen atom.
Thus, for every mole of water, there is exactly one mole of oxygen atoms.