How many molecules are in 0.25 mole of CO? 1) 1.5*10^23
2) 6.0*10^23
3) 3.0*10^23
4) 9.0*10^23

BELOW

Explanation:

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A mole of anything is 6.022 x 10^23 particles

So 0.25 mol CO has 0.25 mol of CO molecules  

0.25 mol CO has 0.25 x 6.022 x 10^23 molecules = 1.5 x 10^23 molecules [to 2 sig figs]

[btw ... if it wanted the number of atoms ... it'd be twice as much because there'd be 0.25 mol of C atoms + 0.25 mol of O atoms ... just be careful what they ask for]

2.00 mol Ni = 2.00 x 6.022 x 10^23 atoms = 1.20 x 10^24 atoms [to 3 sig figs]

HMMM ... looks like you use 6.02 x 10^23 for the mole

so 3.01 x 10^23 atoms He is 0.5 mol He [because He is monatomic]

Molar mass He = 4.00 g

Mass He in sample = 0.5 mol He x (4.00 g He / 1 mol He)

= 2.00 g [to 3 sig figs]

Neon is also monatomic

Molar mass Ne = 20.18 g

Number of mol Ne in sample = 80 g Ne x (1 mol Ne / 20.18 g Ne)

Number of atoms in sample = 80 g Ne x (1 mol Ne / 20.18 g Ne) x 6.022 x 10^23

= 2.4 x 10^24 atoms of Ne [to 2 sig figs]

um hope this is what u meant ^-^

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hope i !