Qualification > Sciences
Edexcel CHEMISTRY DOUBTS!!!!
Blizz_rb93:
This question is from my mock exam but i noticed some questions when i began revising i didnt know how to do it..
so please if anyone can help me understand these questions
2) This question is about two isomeric alcohols, X and Y, each with molar mass 60g mol-1
A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same color change of the mixture on heating.
a) A colorless liquid, B, is distilled from the mixture containing alcohol X.
The liquid B forms a red precipitate when it is boiled with Benedict's or Fehling's solution.
Give the displayed formula of liquid B, and the name of alcohol X.
Liquid B
Name of alcohol X _______________________________
b) A colorless liquid, C, is distilled from the mixture containing alcohol Y.
C does not react when it is boiled with Benedict's or Fehling's solution
Give the names of liquid C and alcohol Y
Liquid C __________________________
Alcohol Y ___________________________
__________________________________________________________________________
That's for question 2, here's question 3.. i know it's kinda long :( but i need help on this so im very sorry
3) This question is about Calcium hydroxide, Ca(OH)2
The solubility of calcium hydroxide in water can be found by titrating a saturated solution of calcium hydroxide with hydrochloric acid of known concentration.
a) Describe how you would make a saturated solution of calcium hydroxide suitable for use in this titration. Do not describe the subsequent titration procedure.
b) 10.0 cm3 portions of the saturated solution are placed in a conical flask and titrated with 0.0500 mol dm-3 hydrochloric acid added from a burette
i) Name the apparatus used to measure the 10.0 cm3 portions
ii) Suggest a suitable indicator for this titration and state the color change you would expect to see at the end point.
c) The following results were obtained
Titration numbers | 1 | 2 | 3 |
_____________________________________________________________________________
Final burette reading/cm3 | 19.20 | 28.05 | 37.10 |
_____________________________________________________________________________
Initial burette reading/cm3 | 10.00 | 19.20 | 28.15 |
_____________________________________________________________________________
Titre/ cm 3 | 9.20 | 8.85 | 8.95 |
____________________________________________________________________________
i) suggest why the first titre should be disregarded.
The rest i know
Thank you all in advance! <33
vanibharutham:
This question is about two isomeric alcohols, X and Y, each with molar mass 60g mol-1
This means that they are isomers of C3H8O
A solution of potassium dichromate(VI) in dilute sulfuric acid is added to each alcohol. Both alcohols cause the same color change of the mixture on heating.
They both were oxidized so it cant be a tertiary alcohol
a) A colorless liquid, B, is distilled from the mixture containing alcohol X.
The liquid B forms a red precipitate when it is boiled with Benedict's or Fehling's solution.
This means that it has been oxidized further so liquid B must be propanal
CH3CH2CHO
And alcohol X must be CH3CH2CH2OH
b) A colorless liquid, C, is distilled from the mixture containing alcohol Y.
C does not react when it is boiled with Benedict's or Fehling's solution
Not oxidized further so it must be Propanone - CH3C=OCH3
And the alcohol Y must be a secondary alcohol CH3CH(OH)CH3
vanibharutham:
3) This question is about Calcium hydroxide, Ca(OH)2
The solubility of calcium hydroxide in water can be found by titrating a saturated solution of calcium hydroxide with hydrochloric acid of known concentration.
a) Describe how you would make a saturated solution of calcium hydroxide suitable for use in this titration. Do not describe the subsequent titration procedure.
Not sure about this one....
Add a known amount of Ca(OH)2 to water and keep stirring. When no more dissolves start heating it. When the solution begins to boil keep adding more Ca(OH)2 while you are still heating it, until no more dissolves.
b) 10.0 cm3 portions of the saturated solution are placed in a conical flask and titrated with 0.0500 mol dm-3 hydrochloric acid added from a burette
i) Name the apparatus used to measure the 10.0 cm3 portions
Pipette
ii) Suggest a suitable indicator for this titration and state the color change you would expect to see at the end point
Phenolphthalein... It is in basic conditions at the start so it will be purple. At the end point it will be colourless
i) suggest why the first titre should be disregarded.
the titre should be disregarded as it was probably a check titration. Furthermore, the titre was more that 0.1cm³ off from the other two values. Titration is a precision method of volumetric analysis and it should be disregarded because it is too far off from the other values
Meticulous:
Jan. 2006. Q. 4(d) and onwards.
Thanks in advance.
Question paper: http://www.xtremepapers.net/Edexcel/Chemistry/2006%20Jan/6243_02_que_20060118.pdf
Mark Scheme: http://www.xtremepapers.net/Edexcel/Chemistry/2006%20Jan/6243_02_rms_20060125.pdf
Needed ASAP.
Tammy:
i have a question about percentage error.....
The balance used to weigh the magnesium carbonate is accurate to +-0.01 g. Calculate the percentage error in the mass of the magnesium carbonate weighed. ((weighed MgCO3: 0.21g))
the correct answer is 0.02
-----
0.21
Why is it 0.02 not 0.01?? and when do we write it as 0.01??
Thanks in advance peeps
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