Answer:
a) 0.001525 mol Ca(NO₃)₂
b) 2.29 × 10²⁴ atoms Mg
General Formulas and Concepts:
Atomic Structure
- Reading a Periodic Table
- Reactions rxn
- Compounds
Explanation:
a)
Calcium (Ca) has a +2 charge on the periodic table. Polyatomic ion for nitrate (NO₃) has a -1 charge. We need to balance the compound:
Ca(NO₃)₂
To find the molar mass of calcium nitrate, we must pull data from the PT.
Ca has a molar mass of 40.08 g/mol
N has a molar mass of 14.01 g/mol
O has a molar mass of 16.00 g/mol
Add these all together and multiply respectively to find the molar mass of the compound:
40.08 + 2[14.01 + 3(16.00)] = 164.1 g/mol
To find the amount of moles we have given grams, divide the grams by the molar mass:
(0.2502 g) / (164.1 g/mol) = 0.001525 mol Ca(NO₃)₂
We are given 4 sig figs and our final answer is in 4 sig figs.
b)
We need to know Avogadro's Number - 6.022 × 10²³ atoms, molecules, formula units, etc. This converts moles into atoms, molecules, formula units, etc.
We are given 3.80 moles of Mg. To find the number of atoms, we multiply Avogadro's number:
3.80 mol Mg · (6.022 × 10²³ atoms Mg/ 1 mol Mg) = 2.28836 × 10²⁴ atoms Mg
Since we are given 3 sig figs, we must round:
2.28836 × 10²⁴ atoms Mg ≈ 2.29 × 10²⁴ atoms Mg
