Below is a question contributed by a local chemistry student (Student X) and an avid reader of this Chemistry Blogsite.
This will be a question that combines Mole Calculations & Qualitative Analysis topics. Give it a try!
Question:
In an experiment, 4.0cm^3 of 1.0mol/dm^3 aqueous copper(II) sulphate was mixed with 8cm^3 of 1.0mol/dm^3 aqueous sodium carbonate:CuSO4 + Na2CO3 –> Na2SO4 + CuCO3
What did the reaction vessel contain when the reaction was completed?
A. A colourless solution only
B. A green precipitate and a blue solution
C. A green precipitate and a colourless solution
D. A blue precipitate and a blue solutionStudent X’s suggested answer:
What I think: copper sulphate is the limiting reactant, hence sodium carbonate is in excess. Hence, when the reaction is completed, only excess sodium carbonate remains. So, the solution remains colourless and my answer is C.
My Suggested Answer:
I agree that the Answer is C. At the end of the reaction, we will see a Green Precipitate of Copper Carbonate(s) which is insoluble in water. There will also be a colourless solution that is contributed by both the product Sodium Sulphate(aq) and the excess reactant Sodium Carbonate (aq) which are soluble in water. (Click the image below to have a clearer understanding)
PS: Check out “Comments” below for Suggested Answers.
Hi.
I agree with you that the answer is C.
You will have Green Precipitate of Copper Carbonate and a Colourless Solution
that is contributed by both the product of Sodium Sulphate (soluble in water)
& excess reactant sodium carbonate (soluble in water).
Cheers
Sean
http://www.SimpleChemConcepts.com
Reply
Always be aware that if there is an excess reactant in the chemical reaction,
there will be the excess reactant that is present in the reaction vessel at the end
of the chemical reaction, together with the product(s).
For this particular question, you can see my suggested answer as shown above.
To your Academic Success in Chemistry,
Sean
Founder & Master Trainer
http://www.SimpleChemConcepts.com
“Experience Learning with A Difference”
Reply
hello!
i would like to ask sth.
cu2+ is a transistion metal right?
i have always thought it always gives blue ppt.
for CuCo3 why is it green ppt? is that under the influence of the carbonate?
thanks!
Reply
Copper metal (Cu) is indeed a Transition Metal and it normally forms the Cu2+ ion.
Do note that NOT ALL Copper Salts have a Blue PPT appearance.
If we have talking about GCE O Levels / N Levels or GCSE (Grade 9/10), i suppose
the Blue PPT refers to the Copper Hydroxide that is formed when you test for Cu2+
cation using alkaline solution such as dilute NaOH and/or Aqueous Ammonia.
Copper Hydorxide has a distinct Blue PPT apperance when the Cu2+ cations reacts with OH- hydroxide anion in the alkaline solution.
Copper Carbonate has a distinct Green Color powder appearance.
Hope this is clear to you.
To Your Academic Success in Chemistry,
Sean
Founder & Master Trainer
SimpleChemConcepts.com
Reply
hi, just need to know what test is used to identify the no3- anion in solution.
ps: ur ans r very informative
Reply
Nitrates can be tested by addition of NaOH + Aluminium Foil and warming the mixtures. Presence of pungent gas and the turning of damp litmus paper blue suggests that ammonia gas is released. Nitrate ions are reduced to Ammonia gas.
Reply
thank u very much sean! this is a gr8 site very helpful, upset i didnt find
it sooner.
Reply
how du calculate percentqge yield and percentage purity?
please include a question for computation in your answer.
Thanks
Reply
thanks alot Sean
I would to know too how to calculate percentage purity ?
The forumula for percentage yield is :
Percentage yield = achieved output/expected output * 100%
or experimental value / theoretical value * 100%
Reply
sean Reply:
October 28th, 2008 at 11:21 am
% Yield = Actual Yield/Theoretical Yield x 100%
whereas
% Purity = Amt of Pure Substance/Amt of Substance used in Rxn x 100%
Hope this helps.
Cheers
Sean
Master Trainer
SimpleChemConcepts.com
Reply
% Yield = Actual Yield/Theoretical Yield x 100%
whereas
% Purity = Amt of Pure Substance/Amt of Substance used in Rxn x 100%
Hope this helps.
Cheers
Sean
Founder & Master Trainer
SimpleChemConcepts.com
Reply
20cm3 of a gaseous hydrocarbon was mixed with 100cm3 of oxygen and the mixture sparked so that the hydrocarbon was completely burnt. The volume of gas remaining at the end of the combustion was 70cm3. After passing over soda lime, this volume was reduced to 10cm3. All gases were measured at 25C and at the same pressure.
(a) What volume of oxygen gas remained unburnt at the end?
(b) What volume of oxygen gas was used in the combustion?
(c) What volume of carbon dioxide was produced in the combustion?
(d) Deduce the formula of hydrocarbon.
Reply
Hey how did you came to know that CUSO4 is the limiting reactant pls reply
Reply
Sir, i thought only iron two plus (Fe2+) will give you green ppt, insted of blue ppt.
I’mma bit confuse here.
Reply
Hi, Na2CO3 and Na2SO4 are colourless solution is it because Na is a group 1 element. and all group 1 salts and ammonium salts are colourless? thanks.
Reply