hw problem 19

[505934309]

Could someone help me with the second part of homework problem 19? I understand that we convert angstrom to m and plug that into the uncertainty equation but somewhere along the way I am messing up. Can someone walk me through what they did step by step because I do not know where I am going wrong, specifically finding the mass of the helium atom because I thought I had it right but I keep getting incorrect answers.

[Kyle_Phong_2J]

Hello,

To find the mass of a helium atom, you take the molar mass and multiply it by 1 mol/Avogadro's number. Remember to also convert this value from g/atom to kg/atom. For the rest of the question, you are correct to convert angstroms to m and plug those values into the uncertainty equation.

[Joyce Meng 2J]

Hello, I think everyone has different numbers for their achieve homework questions, but the general concept is that 1 Angstrom = 10^-10 m. So, if we say that the position of a Helium atom is known within 1.0 A for example, you would use Heisenberg's uncertainty principle that delta x * delta p >= h/pi. Delta p = mass * delta velocity so to rearrange the equation, you get: delta v (minimum) = h/(4pi*mass*delta x) = 6.62608*10^-34/(4pi*6.646*10^-27*10^-10) = 79 m/s. Just like Kyle said, since you said that you are plugging in the numbers into the equation, my guess is that your mass value is 4g = 0.004 kg for the mass of helium. However, the periodic table atomic mass is for a mole of helium, so you would have to divide 0.004 kg by avogadro's number (6.0221*10^23). I hope that helps!