how to solve as the scientific notation

Question

How many moles of hydroxide are in a 255 uL sample of 0.0350 M chromium (III) hydroxide solution? Answer in scientific notation

Answer 1

In order to solve this, we need the formula for Molarity, which is M=mol solute/L solution.

given is:

Volume solution=255 uL=0.255 mL=2.55*10^-3 L solution

Molarity=0.0350 M Cr(OH)₃

Plugging into the equation, we get:

0.0350 M Cr(OH)₃ =x mol solute/2.55*10^-3 L solution

Solving for x

x mol solute= 0.0350 M Cr(OH)₃ * 2.55*10^-4 L solution

Which gives us

0.00000892 mol Cr(OH)3=8.92*10^-6 mol Cr(OH)₃

But we aren't done yet, because it asked specifically for the moles of hydroxide (OH^-). So we multiply the value above by 3 to get:

2.68*10^-6 mol OH^-

If they are looking for the answer in mmol, this would be:

2.68*10^-3 mol OH^-