[simsy]

If i have 2.3445g of PbCr2O7 in a 250mL solution and then took 10mL of that solution and added it to 90mL of a separate water solution, what would the grams of only Pb be in that new 100mL solution?

I started by getting the Molar mass of PbCr2O7: 423.188g and then converted that to moles: 5.4 mol/L but honestly have no idea what to do next.. I have no clue how to figure out how much Pb would be in 10mL of the original 250mL.

Maybe get the MM of Pb only and convert it to moles? I did super well on the starting stoichiometry unit but now with this dilution and concentration stuff i'm almost 100% lost.

Also looked online for a similar problem to this and couldn't find anything close to it

[Babcock_Hall]

There is a mathematically simple formula for dilution calculations, but it is easy to misapply.  My suggest is to draw a picture of the dilution, to avoid using incorrect numbers.  Some common mistakes are to use the wrong volumes or to be inconsistent with respect to units.  Check your class notes to see whether or not your instructor provided you with this equation.

[AWK]

First, let's do rough calculations. Let's bring the sample mass up to 2.5 g and MM up to 500.

2.5 g in 250 mL is equivalent to 10 g per liter, 10 grams of the compound with MM = 500 which is 10/500 or estimated 0.02 moles instead of over 5 calculated by you.

But you have to count the lead content in the diluted solution, not the molar concentration. After dilution, lead does not disappear, so it is the same as in a 10 mL sample. 10 mL from 250 ml is equal to 1/25 the volume of the initial solution and 1/25 the mass of the compound sample, i.e. about 0.1 g. In the compound, lead is slightly less than half the mass, so the expected lead mass in the diluted sample will be less than 0.05 g.
 At the same time, it is a sketch of the solution. Using exact numbers you can check what error I made without the calculator (my guess - about 10%).

[simsy]

well i've been on this problem for hours and feel no closer to getting it done. attempting to post pictures of my work but that doesn't work for whatever reason after making it smaller than 1000 kb and a png file. really feeling like abandoning chem at this point..

[Borek]

You took 10 mL of the original 250 mL volume - that means your new sample contains 10/250th (or just 1/25th) of the 2.3445 grams of the salt. Do you see where it comes from?

All you need to do now is to calculate how many grams of Pb in that amount of salt.

[Babcock_Hall]

The standard dilution formula is C₂=C₁(V₁/V₂).  The concentrations C can be in any convenient unit such as moles per liter or grams per liter.  The quotient V₁/V₂ is the dilution factor.

[AWK]

Dilution is just the wrong title of a discussion thread.

[chenbeier]

I am wondering is lead dichromate existing, in aquaeous Solution und what is its soloubilty.

10 g/l I dont think that can be dissolved. What is the equilibrium between PbCrO₄  und PbCr₂O₇ in Water.

[AWK]

Paper and internet withstand everything
but I found this link without access.
https://materials.springer.com/isp/crystallographic/docs/sd_1910991

[MNIO]

you should be practicing "unit factor method" aka "factor label method" aka "dimensional anlaysis" (to chemistry students) by now.  If you need help with that, there are about a zillion websites that show the process.  In any case, you start with what you're given on the left and convert to what you want on the right.  Like this

you convert from
    100mL dilute solution
you want
    g Pb
you are given this conversion factors
    10mL conc. = 100mL dilute
    2.3445g PbCr2O7 = 250mL conc.

so your conversion is

   100mL dilute         10mL conc.     2.3445g PbCr2O7       207.2g Pb
 ------------------ x ---------------- x ------------------- x ------------------- = __ g Pb
            1               100mL dilute       250mL conc.        423.2g PbCr2O7


start with 100mL dilute
first unit factor is based on 10mL conc = 100mL dilute
the 2nd unit factor is based on 2.3445g PbCr2O7 = 250mL conc.
the 3rd unit factor is the mass fraction of Pb in PbCr2O7

the calcs are easy, just enter
10 * 2.3445 / 250 * 207.2 / 423.2 =
and round to the appropriate sig figs

ans = 0.0459g

*************
There are many benefits of using "dimensional analysis" as the basis to solving chemistry problems.  One of the most important is it gives you a consistent method, starting point and an outline of the process and shows you where the gaps are (what data is missing that you need to look up).  You get good at this and you won't be spending hours trying to solve problems like this.  This took me about 5 minutes to set it up, type it out, calculate mass fraction and chug out the answer. 

ask if you need more help with DA.

[Fish200398]

find molarity of the "250 mL." aka how many mole PbCr2O7 per 250 mL solution.

then we will know in "10 mL" will be how many moles of PbCr2O7, and we know how many mole of Pb then we know how many gram of Pb.

then we add 90mL to the "10 mL" , even if you add 1000 mL or 10 L etc of WATER to the "10 mL", the amount of Pb will be still the same, because you add water not Pb.

cmiiw

[MNIO]

let's see your actual solution Helly

[Babcock_Hall]

let's see your actual solution Helly

I would like to see a solution from the OP.