Question

How many moles are present in 110 grams of LiF? Show your work in the space below

A. 4.2
B. 5.2
C. 2.1
D. 8.4

Answer 1

One equation for the number of moles in a compound:

`number.of.moles = (mass)/(mr)`

(note: Mr is the combined molecular mass of the compound.)

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On the periodic table:

Lithium (Li) has a molecular mass of around 7

Fluorine (F) has a molecular mass of around 19.

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So the total Mr of Lithium Fluoride (LiF) is:

7 + 19 = 26

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Now to work out the number of moles, we just divide the mass (in grams) of the compound by the Mr of the compound (as in the formula):

`number.of.moles = (mass)/(mr)`

`number.of.moles = (110)/(26)`

`number.of.moles = 4.2`

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Answer:

A) 4.2

Answer 2

Answer choice A.

Step-by-step explanation:

Li has an atomic mass of 6.941. F has an atomic mass of 18.998. Combine these to get 25.939 amu/grams. Take the 110 and divide it by 25.939 to get about 4.2. Hope this helps :)