how to find out no of atoms

Question

no of oxygen atom in 10ml of h₂0 (l) 

Answer 1

This question is asking about the number of oxygen atoms in 10 mL of liquid water, so this question might get a little bit more complicated. First, you need to know the number of moles of water that you have. This depends on the density of the water, which depends on the temperature. Assuming that you are at a temperature of 0° C, then the density of water is 1 g/mL. This simplifies things a bit. If the temperature of the water is increased, you will need to check a standard reference source to determine the density of the water. Next we need to convert 10 mL of water into grams, so that we can convert it into moles. Thus,

 

10 mL of H₂O * 1 g H₂O/mL H₂O = 10 g H₂O. Then we need to remember that 1 mol of a substance is equal to its molar mass (which we can use the periodic table to figure out), and if we look that up we know that hydogen has an approximate mass of 1.0079 g/mol and oxygen has an approximate mass of 16.00 g/mol. now these numbers may vary depending on the source that you are using (if they are more or less accurate). Now we multiply the hydrogen molar mass by 2, and add it to the oxygen molar mass, and we find that the molar mass of water is (correcting for significant figures) 18.02 g/mol. Now we can just set up a little equation to find out the number of moles of water.

 

mol H₂O = mass H₂O/18.02 g/mol = 10 g/18.02 g/mol. When we divide, the grams cancel and we are left with moles as the unit.

 

mol H₂O = 0.555 mol

 

Because there is a 1:1 relationship between the number of moles of oxygen and the number of moles of water, we are left with 0.55 moles of oxygen in 10 mL of water. We multiply that by avogadro's number, which is 6.022 * 10²³, and we are left with 3.31 * 10²³ atoms of Oxygen in 10 mL of water. Now I have adjusted for significant figures in this problem at one step, but since I don't initially know how many significant figures you have in the 10 mL of water, I can't do that. So your final answer is somewhere in the neighborhood of 3.31*10²³ atoms.

 

 

Answer 2

At STP 6.022 x 10^23 atoms of any gas will occupy 22.4L” 22.4 L contains 6.022 x 10^23 oxygen atoms 1 L contains 6.022 x 10^23/22.4 oxygen atoms 10/1000 L contains (6.022 x 10^23/22.4)*(10/1000) oxygen atoms =2.68 x 10^20 oxygen atoms in 10ml of water