Question

How many molecules of glucose are in a xenopus oocyte if the total volume is 10 ul and the concentration of glucose is 10 mM?

Answer 1

There are `6.0 × 10^15color(white)(l) "molecules"` of glucose in the oocyte.

Explanation:

The formula for molarity is:

`color(blue)(bar(ul(|color(white)(a/a) "Molarity" = "moles"/"litres"color(white)(a/a)|)))" "`

or

`color(blue)(bar(ul(|color(white)(a/a) M = n/Vcolor(white)(a/a)|)))" "`

In your problem,

`M = "10 mmol/L" = 1.0 × 10^"-3"color(white)(l) "mol·L"^"-1"`
`V = "10 µL" = 1.0 × 10^"-5"color(white)(l) "L"`

∴ `n = MV = (1.0 × 10^"-3"color(white)(l) "mol")/(1 color(red)(cancel(color(black)("L")))) × 1.0 ×10^"-5" color(red)(cancel(color(black)("L"))) = 1.0 × 10^"-8"color(white)(l) "mol"`

Now, we can use Avogadro's number to calculate the number of molecules.

`"Molecules" = 1.0 × 10^"-8" color(red)(cancel(color(black)("mol"))) × (6.022 × 10^23color(white)(l) "molecules")/(1 color(red)(cancel(color(black)("mol")))) = 6.0 × 10^15color(white)(l) "molecules"`