calculate number of atoms in 4.67 mol of Ca(NO3)2
I got:
2.81 X 10^24 C atoms or should it be 28.11 x 10^23 C atoms?
5.62 X 10^24 N atoms or should it be 9.34 x 10^23 N atoms?
1.69 x 10^25 O atoms....but are you allowed to do ^25 or should it be 168.7 X 10^23 O atoms I'm confused about exponents again.
also, do I need to worry about rounding to the correct number of signifcant digits when doing these questions?
Always round to the correct number of significant digits.
Proper scientific notation is X.SY*10^qr
2.84*10^24
5.62*10^24
1.69*10^25 are all correct.
would it have still been right if I didn't change the exponent, and say for C atoms, left it at 28.11 X 10^23?
It is not in correct scientific notation, The number is of course, correct.
To calculate the number of atoms in a given amount of a compound, you need to use Avogadro's number and the molecular formula of the compound.
First, find the molar mass of Ca(NO3)2:
- Calcium (Ca) has a molar mass of approximately 40.08 g/mol.
- Nitrogen (N) has a molar mass of approximately 14.01 g/mol.
- Oxygen (O) has a molar mass of approximately 16.00 g/mol.
Since the compound has two nitrate (NO3) groups, you need to multiply the molar mass of the nitrate group by 2.
Calculating the molar mass of Ca(NO3)2:
Ca - 40.08 g/mol
N - 14.01 g/mol (x2) = 28.02 g/mol
O - 16.00 g/mol (x6) = 96.00 g/mol
Total molar mass = Ca + N + O = 40.08 + 28.02 + 96.00 = 164.10 g/mol.
Now, you have 4.67 mol of Ca(NO3)2. To calculate the number of atoms, you need to multiply the number of moles by Avogadro's number (6.022 x 10^23). Let's calculate the number of atoms for each element in the compound:
1. Carbon (C):
There is no carbon in the compound, so the number of carbon atoms is 0.
2. Nitrogen (N):
Number of moles of N = 4.67 mol
Number of atoms of N = Number of moles x Avogadro's number
Number of atoms of N = 4.67 mol x (6.022 x 10^23) = 2.809 x 10^24 atoms of N.
3. Oxygen (O):
Number of moles of O = 4.67 mol x (2 x 6) = 52.56 mol (Note: There are 6 oxygen atoms in each nitrate group.)
Number of atoms of O = Number of moles x Avogadro's number
Number of atoms of O = 52.56 mol x (6.022 x 10^23) = 3.162 x 10^25 atoms of O.
To answer your questions about the calculated values:
- The value you calculated for the number of carbon atoms is correct. You correctly identified that there is no carbon in Ca(NO3)2, so the number of carbon atoms is 0.
- The value you calculated for the number of nitrogen (N) atoms is correct. It should be 2.809 x 10^24 atoms of N.
- The value you calculated for the number of oxygen (O) atoms is incorrect. The correct value is 3.162 x 10^25 atoms of O. It should be noted that the exponent in scientific notation is multiplied by the factor of 6 (for 6 oxygen atoms in each nitrate group).
About significant digits:
When performing calculations, it is generally advisable to carry out the intermediate calculations with full precision and then round the final answer based on the least precise value given in the problem. In this case, since the original value of 4.67 mol has three significant digits, it would be reasonable to round your final answers to the same number of significant digits.