How do you determine the number of grams?

Question

How many grams of Ca(OH)2 are needed to make 100.0 mL of 0.250 M solution? I'm not exactly sure of how to figure this out, but when I tried it, I got 1.85 g. Is this correct?

Answer 1

First, you have to figure out the number of moles. You want 0.1 L of a solution that has 0.250 moles/L, so you will need to use 0.250 * 0.1 or 0.025 moles of Ca(OH)2.

Next, you need to calculate the molar mass of Ca(OH)2, how much a mole of it weighs. The molar mass of Ca is 40.078 g/mol, for O it's 15.999 g/mol, and for H it's 1.007 g/mol. So the molar mass of Ca(OH)2 is 40.078 + 2*15.999 + 2*1.007 = 74.09 g/mol. So a mole of Ca(OH)2 weighs 74.09 grams.

Finally, you multiply the number of moles (0.025) by the grams per mole (74.09). 74.09 * 0.025 = 1.85 grams.

Congratulations, looks like you got it right!

Answer 2

I wrote out this answer before I calculated, and yes, you're right. If you want the step-by-step, I included it rather than waste it.


First you need to find how many moles of Ca(OH)2 you require.

C = n / V (concentration equals moles divided by volume)

You're given concentration and volume, so:

n = C x V
n = (0.250 M) (.1000 L)
n = 0.0250 mol Ca(OH)2

Now you can convert this into grams:

n = m / M (moles equals mass divided by molar/molecular mass)
m = n x M
m = (0.0250 mol) (40.078 + 2 x 15.9994 + 2 x 1.00794)
m = 1.85 g

Answer 3

By definition, the molar mass is the mass of a mole of a given element / compound. Therefore since: M=m/n where M = molar mass, m = mass, n = moles then m=nM Now, gaseous Nitrogen is a bimolecular gas, N2, Ozone is trimolecular O3 and Xenon is unimolecular Xe. Do the math.

Answer 4

Yes,you are right!!!?
Be confident with yourself!!!!!!

Answer 5

yes! its correct.