Concepts used:
1 mole of an element or a compound has 6.022 * 10²³ formula units
So, we can say that: Number of formula units = number of moles * 6.022*10²³
number of moles of an element or a compound = given mass/molar mass
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003 - Number of CaH₂ formula units in 6.065 grams
Number of Moles:
We know that the molar mass of CaH₂ is 42 grams/mol
Number of Moles of CaH₂ = given mass/molar mass
Number of moles = 6.065 / 42
Number of moles = 0.143 moles
Number of Formula units:
Number of formula units = number of moles * 6.022*10²³
= 0.143 * 6.022 * 10²³
= 0.86 * 10²³ formula units
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004 - Mass of 6.34 * 10²⁴ formula units of NaBF₄
Number of Moles:
We mentioned this formula before:
Number of formula units = number of moles * 6.022*10²³
Solving it for number of moles, we get:
Number of moles = Number of Formula units / 6.022* 10²³
replacing the variable
Number of moles = 6.34 * 10²⁴ / 6.022*10²³
Number of moles= 10.5 moles
Mass of 10.5 moles of NaBF₄:
Molar mass of NaBF₄ = 38 grams/mol
Mass of 10.5 moles = 10.5 * molar mass
Mass of 10.5 moles = 10.5 * 38
Mass = 399 grams
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005 - Number of moles in 9.78 * 10²¹ formula units of CeI₃
Number of Moles:
We have the formula:
Number of moles = Number of Formula units / 6.022* 10²³
replacing the variables
Number of Moles = 9.78 * 10²¹ / 6.022*10²³
Number of Moles = 1.6 / 10²
Number of Moles = 1.6 * 10⁻² moles OR 0.016 moles