Edexcel CHEMISTRY DOUBTS!!!!

[SkyPilotage]

write the formula of compound iron(iii) nitrate(v) ?

Its Fe(NO3)3 --->also called as ferric nitrate.
The 3 for the iron and the 5 is for the nitrogen in the nitrate...

[elemis]

write the formula of compound iron(iii) nitrate(v) ?

The valency of Nitrate is not 5.

[SkyPilotage]

The valency of Nitrate is not 5.

Acutally the 5 is for the Nitrogen so its NO3 where N is +5 and O is -6 so its NO3-
There is also nitrate (iii) where N is +3 and O is -4 so its NO2-..

[elemis]

Acutally the 5 is for the Nitrogen so its NO3 where N is +5 and O is -6 so its NO3-
There is also nitrate (iii) where N is +3 and O is -4 so its NO2-..

Yeah, I know that, but by putting the 5 in brackets right next to the nitrate Nidzzz is implying she thinks the valency of the nitrate ion is -5.

[red_911]

"Calcium nitrate decomposes in a similar way to magnesium nitrate, but at a higher temperature. Explain why the two nitrates have different stability to heat."
unit 2 January 2010 question 16.

in the mark scheme they have told the answer for magnesium nitrate decomposing at higher temperature than calcium nitrate 
correct me if i am wrong 

[Darkstar3000]

This question concerns the titration of a solution of sodium hydroxide with a solution of hydrochloric acid. As the titration proceeds pH of the mixture changes

a) What was the pH when 24.95 cm^3 of 1.00 mol dm^-3 NaOh (aq) had been added to 25 cm^3 of 1.00 mol dm^-3 HCL(aq) ? ANS  : 3

How do I calculate this ? I tried calculation and what I did was -log 2 and subtracted the answer from 14 but it makes no difference. Can you please explain this with as much detail as possible because I'm a bit shakey on this

Thank you

[**RoRo**]

Just a couple of stoichiometry questions!

1. 50cm³ if a solution of citric acid, Mr=192, containing 19.2 g dm^-3 reacted with 50cm³ of a solution of sodium hydroxide containing 12 g dm^-3. Citric acid can be represented by the formula H_xA, where x represents the number of hydrogen atoms in a molecule. Use the data above to calculate the number of moles of sodium hydroxide that react with one mole of citric acid and hence find the find the value of x.

I found the number of moles to be 3 moles, but how do you know that x=3?

2. When 20cm³ of of ammonia gas is passed over a catalyst with excess oxygen, 20cm³ of nitrogen monoxide (NO) and 30cm³ of water vapour are produced. Use this data to write out the equation for the reaction.
Honestly, I did it by just simple balancing - how do you use the data to determine the equation?
The answer is 4NH₃ + 5O₂ -----> 4NO + 6H₂O

3. When 8.4g of sodium hydrogen carbonate are heated 5.30g of solid residue and 1200 cm³ of carbon dioxide are produced and 0.900g of water are evolved. Show that this data is consistent with the following equation.
2NaHCO₃ -----> Na₂CO₃ + CO₂ + H₂O

How do you prove that?

4. Sulphur dioxide can be removed from the waste gases of a power station by passing it through a slurry of calcium hydroxide. The equation for this reaction is:
SO₂(g) + Ca(OH)₂(aq)  -----> CaSO₃(aq) + H₂O(l)
What mass of calcium hydroxide would be needed to deal with 1000dm³ of sulphur dioxide?

I'm getting the answer as 3087.5g, but the answer is supposed to be 324.3 [I'm not sure though, because I copied it down from someone] so can someone please confirm?

5. Chlorine reacts with sodium hydroxide as follows:
Cl₂(g) + 6NaOH(aq) -----> 5NaCl(aq) + NaClO₃(aq) + 3H₂O(l)
What mass of sodium chloride and what mass of sodium(V)chlorate would be produced from 240 cm³ of chlorine gas?
The mass of NaClO₃ is 1.065, but for the mass of NaCl, I'm getting it as 2.925g when also in the paper, I copied it as 2.94g, so which one is right and if it's 2.94, how do you arrive to such an answer?

6. When nitrogen reacts with hydrogen in the Haber process only 17% of the nitrogen is converted to ammonia. What volume of nitrogen and what volume of hydrogen would be needed to produce one tonne of ammonia? (1 tonne = 1 x 10⁶ g)

The answer is supposed to be 4.15x10⁶ dm³ of N₂ and 12.5x10⁶ dm³ of H₂ & I don't know how to arrive to either of the answers!

7. Nitric acid is produced by the following series of reactions:
4NH₃     +    5O₂                     ----> 4NO      +   3H₂O
4NO       +     O₂                     ----> 4NO₂
4NO₂     +    O₂     + 2H₂O      ----> 4HNO₃
What mass of nitric acid would be produced from 17 tonnes of ammonia and what volume of oxygen would be needed in the reaction?
I got the mass right, it's 63 tonnes, but for the volume I'm getting it as 3.05x10⁷dm³ when it's supposed to be 4.8x10⁷dm³!

8. 25cm³ of a solution of an acid H_xA containing 0.1 mol dm^-3 of the acid in each 1000cm³ of solution reacts with 75cm³ of a solution of 0.1 mol dm^-3 NaOH. What is the value of x?
The answer is x=3, I solved this question till I reached to the part where 1 mole of H_xA reacts with 3 moles of NaOH, but I don't know how do you decide that x=3?

Phewww, that's it! I'm very sorry for the length of my post!

[elemis]

Question 1

Write out the ionic equation :

XH⁺ + OH^- ----> H₂O

Since the formula of the acid is H_xA this means it can dissociate and give X Hydrogen ions to neutralise the sodium hydroxide.

Hence, I wrote an in front of the H⁺

Next, calculate the no. of moles of Hyrdogen ions and Hydroxide ions.

Moles of hydrogen ions = moles of acid. Moles of hydroxide ions = moles of NaOH

You have to convert the grams/dm3  to mol/dm3 :

19.2/192 = 0.1 mol/dm3        <---- just divide by the molar mass
12/(23+17) = 0.3 mol/dm3

No. of moles = concentration (calculated above) *volume (in decimetre cube)

You should get 0.015 moles for OH^- and 5*10^-3 moles for H⁺

Insert into the equation and determine the stochiometric ratio :

0.015/(5*10^-3) = 3/1

What this means is that 3 moles of Hydroxide ions are neutralised by ONE mole of the acid.

So the acid must dissociate to give 3 moles of HYDROGEN ions.

Hence, x = 3

Question 2

Write the unbalanced equation :

NH₃ + O₂ ----> NO + H₂O

Calculate the no. of moles of each chemical :

20/24000 = 1/1200 moles of Ammonia and Nitrogen Monoxide

30/24000 = 1/800 moles of Water.

Determine the ratio:

moles of Ammonia : moles of Water = 2:3

Insert this into the equation :

2NH₃ + O₂ ----> NO + 3H₂O

moles of ammonia : moles of NO = 1:1 = 2 : 2

Insert :

2NH₃ + O₂ ----> 2NO + 3H₂O

Balance for oxygen :

2NH₃ + O₂ ----> 2NO + 3H₂O


 

[NidZ- Hero]

Yeah, I know that, but by putting the 5 in brackets right next to the nitrate Nidzzz is implying she thinks the valency of the nitrate ion is -5.

YEAhj i Gt the Point De valency of Nitrogen is -5 Not nitrate 

[SkyPilotage]

YEAhj i Gt the Point De valency of Nitrogen is -5 Not nitrate 

+5

[NidZ- Hero]

How is it possible for chlorine to  The maximum oxidation state of +7?
 

[elemis]

How is it possible for chlorine to  The maximum oxidation state of +7?
 

Reacting hot NaOH and Chlroine gas will cause disproportionation with the Cl attaining an oxidation state of +7 and -1 simultaneously (though in different products).

[**RoRo**]

Question 1

Write out the ionic equation :

XH⁺ + OH^- ----> H₂O

Since the formula of the acid is H_xA this means it can dissociate and give X Hydrogen ions to neutralise the sodium hydroxide.

Hence, I wrote an in front of the H⁺

Next, calculate the no. of moles of Hyrdogen ions and Hydroxide ions.

Moles of hydrogen ions = moles of acid. Moles of hydroxide ions = moles of NaOH

You have to convert the grams/dm3  to mol/dm3 :

19.2/192 = 0.1 mol/dm3        <---- just divide by the molar mass
12/(23+17) = 0.3 mol/dm3

No. of moles = concentration (calculated above) *volume (in decimetre cube)

You should get 0.015 moles for OH^- and 5*10^-3 moles for H⁺

Insert into the equation and determine the stochiometric ratio :

0.015/(5*10^-3) = 3/1

What this means is that 3 moles of Hydroxide ions are neutralised by ONE mole of the acid.

So the acid must dissociate to give 3 moles of HYDROGEN ions.

Hence, x = 3

Question 2

Write the unbalanced equation :

NH₃ + O₂ ----> NO + H₂O

Calculate the no. of moles of each chemical :

20/24000 = 1/1200 moles of Ammonia and Nitrogen Monoxide

30/24000 = 1/800 moles of Water.

Determine the ratio:

moles of Ammonia : moles of Water = 2:3

Insert this into the equation :

2NH₃ + O₂ ----> NO + 3H₂O

moles of ammonia : moles of NO = 1:1 = 2 : 2

Insert :

2NH₃ + O₂ ----> 2NO + 3H₂O

Balance for oxygen :

2NH₃ + O₂ ----> 2NO + 3H₂O


 

Thank you very much for your help, I really appreciate it!

[**RoRo**]

Another question guys, added to my previous set of questions!

What's the explanation for the fact that the more branched the molecules in the fractions of crude oil are, the more useful the fuel is? Is it the fact that they have a lower boiling point because they'd have less intermolecular forces between the molecules as a result of the smaller surface area? 

[Master_Key]

Another question guys, added to my previous set of questions!

What's the explanation for the fact that the more branched the molecules in the fractions of crude oil are, the more useful the fuel is? Is it the fact that they have a lower boiling point because they'd have less intermolecular forces between the molecules as a result of the smaller surface area? 

I think shorter chain fuels are more useful. The branch can then be explained that when cracking these branched chain alkanes/alkenes they give useful product. The latter is correct. Your concept of intermolecular force is correct.

Gasoline(4-8 Carbon atoms).