Question

How many moles of NaOH are present in 19.0 mL of 0.150 M NaOH?

Answer 1

`"0.00285 moles"`

Explanation:

Molarity is defined as moles of solute, which in your case is sodium hydroxide, `"NaOH"`, divided by liters of solution.

`color(blue)("molarity" = "moles of solute"/"liters of solution")`

SImply put, a `"1-M"` solution will have `1` mole of solute dissolved in `1` liter of solution.

Now, you know that your solution has a molarity of `"0.150 M"` and a volume of `"19.0 mL"`.

Since the volume is much smaller than `"1 L"`, you can expect to have fewer moles of sodium hydroxide in this sample than you would have had in a full liter of solution.

Convert the volume of the sample from mililiters to liters by using the conversion factor

`"1 L" = 10^3"mL"`

to get

`19.0color(red)(cancel(color(black)("mL"))) * "1 L"/(10^3color(red)(cancel(color(black)("mL")))) = 19.0 * 10^(-3)"L"`

This means that the number of moles of solute you get in this sample will be equal to

`color(blue)(c = n/V implies n = c * V)`

`n = 0.150"moles"/color(red)(cancel(color(black)("L"))) * 19.0 * 10^(-3)color(red)(cancel(color(black)("L"))) = color(green)("0.00285 moles NaOH")`