Chemistry problem. heeelp

[Mo0o]

Ok, my partner and i are kinda stumped. heres the prob

We have the mass of an unknown at .525g its eithe NaHCO3 or KHCO3

After putting the crap through HCl then evaportaing the H2O we got it to .485g so now its either NaCl or KCl


and heres the givens
106g Na2 CO3 --> 97 g NaCl ~mass ratio 1:1
138g K2 C)3 --> KCl ~mass ratio 1:1

how can we determine whether the final substance is either KCl or NaCl

 

[Mo0o]

^^

 

[Robert01]

Determine the # of moles in each reaction and then convert that to grams...something like that. (ie start by using the molecular weight and convert to the grams of moles in the reaction).

Of course, I'm probably wrong, so don't listen to me. At all. Period.

 

[j0lly]

If all you want to do is to distinguish between K+ and Na+ you can do the following:

Make solutions of both the salts.

1) add 2-3 drops of potassium pyroantimonate sol. to the your salt solution and scratch the sides of the test tube. If you get a white crystalline ppt., Na+ is confirmed.

2) add 2-3 drops of picric acid solution and scratch the sides of the test tube. If you get a yellow crystalline ppt., K+ is confirmed.

Note: ppt--> percipitate. Gently scratch the sides with a glass rod (no metals). use a strong salt solution.

//keep the ratio of solutions 1:1.

 

[rgwalt]

Questions:

did you make sure everything was precipitated out of the solution? Did you decant (pour off) the leftover "water" before drying the solid? The leftover "water" is actually a salt solution as well, so I hope you poured it off before drying the solid.

Anyway, you need to determine how many moles of each substance you would have had when you started, then determine how many moles of product you would have had when you were finished. Then determine the weight of product from the number of moles. Which ever scenario matches the final weight you determined is the correct starting material.

Ryan

 

[richardycc]

<< Ok, my partner and i are kinda stumped. heres the prob

We have the mass of an unknown at .525g its eithe NaHCO3 or KHCO3

After putting the crap through HCl then evaportaing the H2O we got it to .485g so now its either NaCl or KCl


and heres the givens
106g Na2 CO3 --> 97 g NaCl ~mass ratio 1:1
138g K2 C)3 --> KCl ~mass ratio 1:1

how can we determine whether the final substance is either KCl or NaCl >>




what was the given of 138g K2co3 --> KCl? If it is 127.48 than the final substance is KCl (138g * .485g) / .525g = ~127.49g

if 106g of naco3 will give you 97 g of nacl then .525g of nahco3 should give you about .480 ( 97g * .525g ) / 106g = .480g


hope this makes sense to you.

rich

 

[flashbacck]

<< Determine the # of moles in each reaction and then convert that to grams...something like that. (ie start by using the molecular weight and convert to the grams of moles in the reaction).

Of course, I'm probably wrong, so don't listen to me. At all. Period. >>



sounds right to me