Question

hi, Im not sure how to explain this well but here goes.

Im doing a oxidization/reduction reaction to determine the charge of an element.

charge is n

formula n=a/b

Problem:

0.6215 g sample of nickle metal was dissovled in 100.0ml of fe 3+

Note for the formulas: I put all the charges in bracket cause i don't know how to make superscripts.

aFe(3+)(aq) +bNi(aq)--> aFe(2+)(aq) + bNi (+n) (aq)

15.00 ml sample of this solution was taken and titrated. If it took 26.48ml of 0.0200 M Cr2O7(2-)


Heres the other formula for dichromate

6fe(2+) + cr207 (2-)--->c + d


step 1) Find the moles Ni

= .6215 x mol/55.84= 1.06 x 10-2 mol

This is the part im having problems with. Since only 15 ml were used i did the following:

1.06 x 10-2 x 15.00/100.00= 1.59 x 10-2Ni

that gives me b

step 2)Now find the moles of fe

so i did the following:

26.48ml x 0.0200M x 6fe(2+)/1mol cr207(2-) x 1mol fe (3+)/1 mol fe(2+)

a= 3.18 x 10(2-) fe(3+)

step 3) finally, N=a/b

3.18 x10-2/1.59 x10-2=2

If it confuses you i can just simplify it to the part im having problems with.

Answer 1

Heres the simplified version:


I need to convert Ni to moles:

I have a 0.6215 g sample of Ni that was dissolved in 100.00ml of Fe 3+. Then, 15.00 ml of the sample was taken and titrated. It took 26.48 ml of .0200M Cr2072- to titrate the solution.
]

I did the following to find the moles of Ni

0.6215g x M/58.69g=1.06 x 10-2 mol

1.06 x 10 -2 mol x 15.00 ml/100.00ml= 1.59 x 10-2 mol

thanks again dan

Answer 2

#1. I can't make out what you are trying to do. Some suggestions for future posts.
a. Type with i caps (as in I), Fe and not fe, Cr2O7 and not cr2O7.

b. For the charge on the ions, use the carat. Fe^3, Cr2O7^-2, Ni^+2, etc.

c. The atomic mass for Ni is not 55.84 but 58.69

d. Carry the division for moles Ni (0.6215/58.69 = 0.010595 which I would leave in the calculator as is but you have four significant figures and I would use them if I rounded to 0.01060.

e. Write the problem, THEN show how you solved it.

Answer 3

I only need help with step 3

We are trying to figure out the charge on Nickel. So we performed titrations.

First, 0.6215 g sample of nickle metal was dissovled in 100.0ml of Fe^3+.(acid based)


Then, 15.00 ml sample of this solution was taken and titrated. If it took 26.48ml of 0.0200M Cr2O7^2-

Step 1)
Find n

=using algebra i got the following
=aFe^3+(aq) +bNi(aq)--> aFe^2+(aq) + bNi ^n+(aq)

=3a + b0 for the reactants and 2a + bn for the reactants
=3a +b0 =2a +bn

solving for n.
=n=a/b

Step 2) Find the moles of Fe^ 3+


Fe^2+ = fe^3+ (from the formula above). Therefore, if we know Fe^2+ we know Fe^3+

Fe^2+ was titrated with dichromate. 26.48ml of 0.0200M Cr2O7^2 The formula is

6fe^2+ + cr207^2- = c + d

Theefore, 0.02648L x 0.0200M x 6mol Fe^2/1mol Cr2o7^2- x1 Mol Fe^3+/1 mol Fe^2+
= 3.18 x 10^-2 Mol Fe^3+

thats a


step 3)This is the part i'm having problems with. I need to find the moles of b. This is the moles of Nickel. I converted the grams of nickel to moles. Since we only used 15.00ml of 100.00 ml I wrote the following:

= 0.6215 g Ni x 1 mol/58.69g x 15.00 ml/100 ml

=1.59 x10-2 mol

step 4)
solve for n=a/b

3.18 x10^-2/1.59 x 10^-2

=2

So the charge on Nickel(for the products is 2. Then, i got to balance the equation.

Hope this helps. Thanks Dan