How many millimoles of Ca(NO3)2 contain 3.1 × 1021 formula units of Ca(NO3)2? The molar mass of Ca(NO3)2 is 164.10 g/mol.
The Correct Answer and Explanation is:
To find how many millimoles of Ca(NO₃)₂ contain 3.1 × 10²¹ formula units, we can follow these steps:
- Determine the number of moles from the number of formula units:
Avogadro’s number (6.022 × 10²³) tells us how many formula units are in one mole of a substance. We can use this to convert from formula units to moles. Formula: moles=formula unitsAvogadro’s number\text{moles} = \frac{\text{formula units}}{\text{Avogadro’s number}}moles=Avogadro’s numberformula units Substituting the given values: moles of Ca(NO₃)₂=3.1×10216.022×1023≈5.15×10−3 moles\text{moles of Ca(NO₃)₂} = \frac{3.1 \times 10^{21}}{6.022 \times 10^{23}} \approx 5.15 \times 10^{-3} \text{ moles}moles of Ca(NO₃)₂=6.022×10233.1×1021≈5.15×10−3 moles - Convert moles to millimoles:
Since 1 mole = 1000 millimoles, we can convert moles to millimoles by multiplying by 1000. millimoles of Ca(NO₃)₂=5.15×10−3×1000=5.15 millimoles\text{millimoles of Ca(NO₃)₂} = 5.15 \times 10^{-3} \times 1000 = 5.15 \text{ millimoles}millimoles of Ca(NO₃)₂=5.15×10−3×1000=5.15 millimoles
Thus, 3.1 × 10²¹ formula units of Ca(NO₃)₂ correspond to approximately 5.15 millimoles.
Explanation:
We first used Avogadro’s number to convert from formula units to moles. Avogadro’s number is a constant that links the number of particles (atoms, molecules, or formula units) to the amount of substance in moles. Once we found the number of moles, we multiplied by 1000 to convert to millimoles, as the problem asked for the answer in millimoles rather than moles. This type of calculation is common in chemistry when dealing with amounts of substances on a molecular scale.
