How do i know when to use grams or milligrams in calculations?

"What mass of silver nitrate is required to be weighed out to prepare 250 mL of a 0.125M solution?"

This is my understanding so far:

mass of solute = concentration x volume of solution
= 0.125 x 250
= 31.25??

I'm hoping that I've calcaulated it right, but what I'm really stuck on is which unit I should use. would it be in g or mg?

Many thanks!

Answer:
It is not right because
Molarity = moles solute / L solution
250 mL = 0.250 L
moles of solute = 0.125 x 0.250 = 0.0312

Molar mass AgNO3 = 169.87 g/mol
0.0312 mol x 169.87 g / mol = 5.30 g of AgNO3 needed

Note : look at significant figures : there are 3 significant figures so in any case 31.25 is not right because it has 4 significant figures
i think its mg.
when concentration is in molar the mass is in grams in relation to litre.
here,it is grams*millilitre=milligrams
so th unit is mg.
31.468 grams of silver nitrate

250mL = 250cc's
250 X .125 =31.25cc's
31.25 cc's X 1.007(density of silver nitrate) = 31.468 grams

I hoped this helped. :)

The answers post by the user, for information only, FunQA.com does not guarantee the right.



More Questions and Answers:
  • How would I draw the constitutional isomer of CH3CH=CHCH3.?
  • Evaluate Keq.?
  • Organic chemistry? Writing reactions with Bromine and hydrocrabons?
  • What is alka yagnik email id?
  • Does some one know how milk get the white color and what thing give that characteristic?
  • A tarnished copper vessel begins to shine when rubbed with lemon .Why?
  • Help!!?
  • In a particular chemical reaction 2 bonds are broken and no bonds are formed. Based only on this information..
  • Wat does the elements dat exists as molecules called?