quick question! :(

Heyyyy

anyone know how to answer this questions:

how many molecules of insulin (MW=5807.67) are there in 25 ul(micro litres) of a 0.3mM solution of insulin?
:confused:

is how many molecules simply asking me the mass? so i do mass = molarity x MW x volume equation? or is this wrong?

Reply 1

Seth

Mede

Heyyyy

anyone know how to answer this questions:

how many molecules of insulin (MW=5807.67) are there in 25 ul(micro litres) of a 0.3mM solution of insulin?
:confused:

is how many molecules simply asking me the mass? so i do mass = molarity x MW x volume equation? or is this wrong?

NO, it's asking you the number of molecules. First of all work out how many molecules you have in a mole then divide to work out the amount in 25 micro litres of the 0.3mM solution.

You'll need to use: Number of molecules = Number of moles * 6.022 x 10^23 (Avogadro's constant).

Reply 2

Mede

Thanks for your reply :smile:

i worked out the number of molecules:

Number of moles = molarity x volume
number of moles = 0.3mM x 25 ul
number of moles = 7.0^-9

But then why has it given me the Molecular weight? :confused:

Or i have a better idea, could it be?

mass = molarity x MW x volume
mass = 0.3mM x 5807.67 x 25 ul
mass = 4.4 ^ -5

thus:

number of moles = mass/MW
number of moles = 4.4 ^-9 / 5807.67
number of moles = 7.6 ^-13

:redface: