ALEKS - Solving Limiting Reactant Problems in Solution - 2 of 2 (harder version)

[candicemertz]

Hi, I have a question regarding correlating the steps from this video to another problem from Aleks.

Suppose 6.89g of sodium bromide is dissolved in 350.mL of a 61.0 mM aqueous solution of silver nitrate.
Calculate the final molarity of sodium cation in the solution. You can assume the volume of the solution doesn't change when the sodium bromide is dissolved in it.

I first set up the equation of NaBr + NaNO3 + AgBr
I was confused right away because the problem asks you to look at the sodium cation and NaNO3 is soluble know what to do and just ignored the equation because it doesn't seem to be necessary to solve.

Then I took the 6.89 g NaBr x 1 mol/ 102.89g = 0.66696 mol NaBr (so far the same as Aleks)
Then I calculated mol for AgNO3: 0.061x0.350= 0.02135 mol (for some reason Aleks does not do this step?) This is how I determined NaBr will be in excess.

So like the video with the solution being the limiting reactant I took the moles of NaBr and subtracted the moles of AgNO3 and then divided that amount by L to determine molarity. Which was apparently not correct for this problem.
The steps from Aleks just shows finding moles for NaBr and then simply dividing that by L to get molarity.

I am confused when you subtract the moles of the excess reactant and the limiting reactant?

Thank you for your time!!
Candice

[emiliestansbury]

Followed all the steps and still got the answer wrong fml

[karroten]

Thank you for posting these -- you're essentially translating the sometimes-poor syntax of the ALEKS explanations into something much more understandable. Much appreciated!

[erintodd]

Hi, hopefully this comment isn't too new to be answered! What if no precipitate is formed? My problem is a reaction between NaCl and K2CO3, which I think form two soluble compounds. Do you simply divide the initial moles by the volume? Or do I need to do limiting reactant stuff. If I do need to do limiting reactants, could you explain how I would do it? Or just let me know if I am wrong about there not being a precipitate. Thank you very much!

[erintodd]

Hi, hopefully this comment isn't too new to be answered! What if no precipitate is formed? My problem is a reaction between NaCl and K2CO3, which I think form two soluble compounds. Do you simply divide the initial moles by the volume? Or do I need to do limiting reactant stuff. If I do need to do limiting reactants, could you explain how I would do it? Or just let me know if I am wrong about there not being a precipitate. Thank you very much!

[antsgotpetsagp]

Where does the the 119g come from in the equation 2.61g *1mol/119g thank you

[emmakistner]

What do I do if there is no precipitate that forms???

[madelinea]

could you do stoichometry "limiting reactants"?

[noahross]

Thank you very much for the explanation!!

[VanquilFtw]

So what's the significance of determining whether or not its a precipitate