1. Which sample contains the greatest number of atoms?
10.0 g He
25.0 g Ne
115 g Xe
2. A mothball, composed of naphthalene C10H8 has a mass of 1.74g.
How many naphthalene molecules does it contain?
3.A salt crystal has a mass of 0.20 mg .
How many NaCl formula units does it contain?
10.0 g He
25.0 g Ne
115 g Xe
2. A mothball, composed of naphthalene C10H8 has a mass of 1.74g.
How many naphthalene molecules does it contain?
3.A salt crystal has a mass of 0.20 mg .
How many NaCl formula units does it contain?
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Pretty easy, you're using the formulas (n=m/M) and (N=n x NA).
So with question 1a for example, n=10.0/4.0 = 2.5mol, then use N=2.5 x (6.02x10^23)=1.505x10^24 atoms, you do EXACTLY the same for the other 2, and see if they are greater than the 1.505x10^24.
Question 2, you do exactly the same, work out n in moles, then use the second formula to find the number of molecules.etc
You will get large numbers like 10^24, if you do then this is correct. Hope I helped.
So with question 1a for example, n=10.0/4.0 = 2.5mol, then use N=2.5 x (6.02x10^23)=1.505x10^24 atoms, you do EXACTLY the same for the other 2, and see if they are greater than the 1.505x10^24.
Question 2, you do exactly the same, work out n in moles, then use the second formula to find the number of molecules.etc
You will get large numbers like 10^24, if you do then this is correct. Hope I helped.
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The molar or formula unit mass contains 6.022 X 10^23 atoms of an element or molecules of a compound or formula units of a compound. Compute the molar masses and take the appropriate fraction or multiple of the Avogadro number