Quantitative chemistry Flashcards

1
Q

true or false
the Mr of a compound is always greater than the Ar of any of the elements in that compound

A

true
you find the Mr by adding up the Ar of each element so it must be greater

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2
Q

the Ar of oxygen is 16 and the Ar of nitrogen is 14. find the Mr of nitric oxide, NO

A

14 + 16 = 30.
there’s only one atom of each element in the formula so just add the Ar values together

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3
Q

how do you calculate the percentage mass of an element in a compound

A

multiply the Ar of the element by the number of atoms of that element in the formula of the compound. then divide by the compounds Mr and multiply by 100.

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4
Q

the formula of the compound sulfur hexafluoride SF6.
calculate the Mr of sulfur hexafluoride.
Ar of F = 19
Ar of S = 32

A

32 + (19 x 6) =
32 + 114 =
146

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5
Q

what is the definition of a mole

A

one mole is 6.02 x 10^23 (Avogadro constant) particles of a substance

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6
Q

what is the formula for the number of moles in a given mass

A

number of moles = mass in grams / Mr

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