[sarah9625]

How do I determine the volume of a 3M stock NaOH solution that I will need to dilute to 1L to obtain a 0.1M solution?

Some website told me to do Vi x Mi = Vf x Mf, that would be 1L x 3M / 0.1M = thats like 300L that can't be right.

Also, How do I estimate what volume a 0.1M solution of NaOH that will be required to titrate to 0.300g of KHP to its endpoint?

[Padfoot]

How do I determine the volume of a 3M stock NaOH solution that I will need to dilute to 1L to obtain a 0.1M solution?

Some website told me to do Vi x Mi = Vf x Mf, that would be 1L x 3M / 0.1M = thats like 300L that can't be right.

Your Vi and Mi must correspond to the same solution. 
So it would be Vi*3=1*0.1
Note that this eqn works because n(NaOH) is constant.

[sarah9625]

so that would give 3.33ml, right?

Also for the other question I posted...
if I can use the same equation I would get 1L x 0.300g=Vfx x 40g = 7.5ml
That sounds wrong to me.

Doe you have any other formulas or suggestions?

Thanks for ANY *delete me*

[Sev]

so that would give 3.33ml, right?

no.  33.33mL.

Q2.  Use another method.  Start by working out the number of mole of KHP in 0.3g

[sarah9625]

Is this how to find the moles:

204.22g/m   / 0.3g   =   681 moles?

now what?

[Padfoot]

Is this how to find the moles:

204.22g/m   / 0.3g   =   681 moles?

now what?

Number of moles= your mass/mass of 1 mol  (n=m/M)
This eqn makes sense.  Recalculate moles with this eqn.
The next step would be to write the chemical reaction eqn (these are often your first steps for stoichiometry problems). 
You should be able to solve from here.

Also for the other question I posted...
if I can use the same equation I would get 1L x 0.300g=Vfx x 40g = 7.5ml
That sounds wrong to me.

The eqn Mi*Vi=Mf*Vf only applies to dilution type problems like Q1.  Think about how/why the eqn works (see my last post) and you will see why the eqn can't be used for this question.

Hope that helps 

[sarah9625]

so that would be 40g / 0.300g = 133.33 moles
or
204.22g / 0.300g = 681 x 33.33ml / 0.1moles?

not sure what you mean by the next step?

[Padfoot]

so that would be 40g / 0.300g = 133.33 moles
or
204.22g / 0.300g = 681 x 33.33ml / 0.1moles?

You have 0.300 grams of KHP.  Now every mole of KHP has a mass of 204.22 grams.  You therefore have (0.300/204.22) mol of KHP which is 0.00147mol.

not sure what you mean by the next step?

Write down the reaction that takes place between the KHP and NaOH.
NaOH(aq) + KHC8H4O4(aq)→ H2O(l) + KNaC8H4O4(aq)

From the above, we can see that the molar ratio is 1:1
(which simply means that every mol of NaOH will react with 1 mol KHP).
Using this 1:1 ratio, we know that the amount of NaOH that is required to react with our KHP is 0.00147mol.

So now all you have to do is work out how much of the 0.1molL^-1 solution of NaOH is needed to get this amount.
Hint: n=cv
       v=n/c
 

not sure what you mean by the next step?

General hint: Don't lose sight of the question.


 

[sarah9625]

Okay, so...
 0.1mol/L  /   0.00147mol  =  68L

That is right, right?

[Padfoot]

You've got it the wrong way around.
It should be (0.00147/0.1)L which is 0.0147L or 14.7mL.

v=n/c   
(v=volume, n=number of mol=0.00147, c=concentration=0.1molL^-1).

[sarah9625]

Thank you VERY VERY much. This stuff I harder than I remember. I am repeating this after taking it too many years ago. I guess credits have an expiration date according to the colleges.

Thanks for your help,
Sarah

[enahs]

You might find it useful to search google for "Dimensional analysis" and study up on it.