GCHEM Help needed !

[Thuy]

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Hey guys,

Im having hard time to solve one G-CHEM questionfrom Barrons' practice test.

What mass of styrene ( molar mass = 104.1 ) will contain 4.5 x 10^20 molecules of styrene ? Answer: 7.78 x 10^-2 g

I tried to convert molecules to moles using Avogadro's #, then multiply moles by molar mass, but I didnt find a reasonable answer. Also, the calculation looks too complicated to be true x___x

Thank you for your help !

 

[Dentite99]

Hey guys,

Im having hard time to solve one G-CHEM questionfrom Barrons' practice test.

What mass of styrene ( molar mass = 104.1 ) will contain 4.5 x 10^20 molecules of styrene ? Answer: 7.78 x 10^-2 g

I tried to convert molecules to moles using Avogadro's #, then multiply moles by molar mass, but I didnt find a reasonable answer. Also, the calculation looks too complicated to be true x___x

Thank you for your help !

Not an easy one, but i think your method is right, just be careful with the numbers. First divide the molecules by avagardos # = 4.5 x 10^20 / 6 x 10^23 = 7 x 10 ^-4; then multiply that by the MM = 7.2 x 10^-2. (close enough w/o a calc).

 

[anteater85]

Hey dude,
Here is simplest way that I used to solve the question:

To get the number of atomes just divide the 4.5 x 10^20 by the avogadro's number(6.022 x 10^23). which gives you 0.00074726

then multiply 0.00074726 by the molar mass and you'll get your answer.

Hope I helped

Hey guys,

Im having hard time to solve one G-CHEM questionfrom Barrons' practice test.

What mass of styrene ( molar mass = 104.1 ) will contain 4.5 x 10^20 molecules of styrene ? Answer: 7.78 x 10^-2 g

I tried to convert molecules to moles using Avogadro's #, then multiply moles by molar mass, but I didnt find a reasonable answer. Also, the calculation looks too complicated to be true x___x

Thank you for your help !

 

[Thuy]

Hey

I knw what i got wrong ==> AVOGRADO's Number. I dnt knw why i thought it was 2 x10^23 !
Anyway, than you so much for your help !