Questions - help needed urgent (1 Viewer)

[Petinga]

1. A student carried out an investigation to analyse the sulfate content of lawn fertiliser. The student weighed out 1.0g of fertiliser and dissolved it in water. 50 ml of 0.25mol per litre of barium cholride soluition was added. A white preciptiate of barium sulfate formed with mass 1.8g
a)calculte % by mass of sulfate in fertiliser
b) asses reilabilty of procedure

2. A houselhood cleaning agent contains a weak base og genral formula NaX. 1.00g of this compouind was disolved in 100mL of water. A 20mL samlpe of the solution was titrated witrh 0.1000mol per litre HCl and required 24.4 mL of acid to neutralise.
a) what is molar mass of this base

 

[Riviet]

2. A houselhood cleaning agent contains a weak base og genral formula NaX. 1.00g of this compouind was disolved in 100mL of water. A 20mL samlpe of the solution was titrated witrh 0.1000mol per litre HCl and required 24.4 mL of acid to neutralise.
a) what is molar mass of this base

Okay... this was quite tricky, but I'm so happy to have figured it out for us.

n(_HCl) = cV
= 0.1000 x 0.0244
= 0.00244 mol.

Now the ratio of the number of moles of HCl that reacts to NaX is 1:1,
.'. n(_NaX) = 0.00244 mol.

So in 20ml [or 0.020 L] of the NaX solution,
C(_NaX) = n/V
= 0.00244/0.020
= 0.122 mol/L

Now, we realise that the concentration of a solution doesn't change if we pour out any volume of it into another beaker. For example, if you have a 100ml of 0.1 mol/L orange juice and pour out 60ml into another cup, the concentration doesn't change, only the volume and number of moles.

So now we find the number of moles of NaX in 101ml [or 0.101 L] of water since 1g=1ml and that's the total volume when you dissolve 1ml of NaX in 100ml of water.

n(_{101ml or 0.101L NaX}) = cV
= 0.122 x 0.101
= 0.012322 mol.

Now remember that n = M/m, where M is the mass (grams) and m is the molecular mass. Rearranging this we get:
m(_{1 gram NaX}) = M/n
= 1/0.012322
= 81.2 g/mol (3 sig fig)

That should be right. If you have any questions on my working, feel free to ask.

 

[.ben]

Where'd you get these question from Petinga? was it from tipps?

 

[xx06]

huh? where did you get the mole ratio of NaX to HCL to 1:1????

 

[insert-username]

huh? where did you get the mole ratio of NaX to HCL to 1:1????

If there's only one sodium atom, the ratio must be 1:1 since sodium has a valency of 1.


I_F