Turn on thread page Beta
    • Thread Starter
    Offline

    17
    ReputationRep:
    When ammonium dichromate(VI) is added gradually to molten ammonium thiocyanate, Reinecke’s salt is formed. It has the formula NH4[Cr(SCN)x(NH3)y] and the following composition by mass:

    Cr - 15.5 %
    S - 38.15 %
    N - 29.2 %.

    (a) Calculate the values of x and y in the above formula.

    Thanks
    • Thread Starter
    Offline

    17
    ReputationRep:
    can anyone answer, it's very important
    • Thread Starter
    Offline

    17
    ReputationRep:
    anyone...
    Offline

    10
    ReputationRep:
    You need to work out the ratios of each element you can, being N, S and Cr.

    You do this by finding the molar ratios (working out the moles and then dividing the largest by the smallest ones)- kinda like empirical formula

    =Percentage given in the question divided by atomic weight
    Cr: 15.5 / 51.9 = 0.29
    =Divide the moles of both sulphur and nitrogen by 0.29
    S: 1.19 / 0.298 = 4
    N: 2.08 / 0.298 = 7

    This gives us ratios of number of atoms in the WHOLE compound

    S: 128 / 32. = 4

    N: 97 / 14 = 7

    This means there are a total of 4 sulphur and 7 nitrogen atoms in the compund. resen in the complex. SCN has 4 of the 7 nitrogen atoms and NH4 has another, so that leaves 2.

    overall= NH4[Cr(SCN)4(NH3)2]


    i hope that makes sense
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by ionicbond)
    You need to work out the ratios of each element you can, being N, S and Cr.

    You do this by finding the molar ratios (working out the moles and then dividing the largest by the smallest ones)- kinda like empirical formula

    =Percentage given in the question divided by atomic weight
    Cr: 15.5 / 51.9 = 0.29
    =Divide the moles of both sulphur and nitrogen by 0.29
    S: 1.19 / 0.298 = 4
    N: 2.08 / 0.298 = 7

    This gives us ratios of number of atoms in the WHOLE compound

    S: 128 / 32. = 4

    N: 97 / 14 = 7

    This means there are a total of 4 sulphur and 7 nitrogen atoms in the compund. resen in the complex. SCN has 4 of the 7 nitrogen atoms and NH4 has another, so that leaves 2.

    overall= NH4[Cr(SCN)4(NH3)2]


    i hope that makes sense
    Thanks for responding but i don't really get it, what does the 0.29 represent. Does it mean Cr has 0.29th of an atom in it as Cr has only one atom?
    And you already found the moles of s and n ( 4 and 7) then why did you do for e.g. 128/32=4 again? (where did you get 128 and 97 from) I hope you get what I mean.
    Offline

    10
    ReputationRep:
    (Original post by GCSE 9)
    Thanks for responding but i don't really get it, what does the 0.29 represent. Does it mean Cr has 0.29th of an atom in it as Cr has only one atom?
    And you already found the moles of s and n ( 4 and 7) then why did you do for e.g. 128/32=4 again? (where did you get 128 and 97 from) I hope you get what I mean.

    I see what you mean. sorry that was unclear. i will work it again:


    so: N= 29.2/14= 2.08 moles of N in compound
    S: 38.15/32=1.19 moles of S in compound
    Cr: 15.5/51=0.29 MOLES OF CR IN COMPOUND

    Divide everything by 0.3. That gives you;

    N=7
    S=4
    Cr=1

    Therefore, there are 4 of S and 7 of N
    • Thread Starter
    Offline

    17
    ReputationRep:
    (Original post by ionicbond)
    I see what you mean. sorry that was unclear. i will work it again:


    so: N= 29.2/14= 2.08 moles of N in compound
    S: 38.15/32=1.19 moles of S in compound
    Cr: 15.5/51=0.29 MOLES OF CR IN COMPOUND

    Divide everything by 0.3. That gives you;

    N=7
    S=4
    Cr=1

    Therefore, there are 4 of S and 7 of N
    Thank you so much i get it know ))
 
 
 

University open days

  1. University of Bradford
    University-wide Postgraduate
    Wed, 25 Jul '18
  2. University of Buckingham
    Psychology Taster Tutorial Undergraduate
    Wed, 25 Jul '18
  3. Bournemouth University
    Clearing Campus Visit Undergraduate
    Wed, 1 Aug '18
Poll
How are you feeling in the run-up to Results Day 2018?
Help with your A-levels

All the essentials

The adventure begins mug

Student life: what to expect

What it's really like going to uni

Rosette

Essay expert

Learn to write like a pro with our ultimate essay guide.

Uni match

Uni match

Our tool will help you find the perfect course for you

Study planner

Create a study plan

Get your head around what you need to do and when with the study planner tool.

Study planner

Resources by subject

Everything from mind maps to class notes.

Hands typing

Degrees without fees

Discover more about degree-level apprenticeships.

A student doing homework

Study tips from A* students

Students who got top grades in their A-levels share their secrets

Study help links and info

Can you help? Study help unanswered threadsRules and posting guidelines

Groups associated with this forum:

View associated groups

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Write a reply...
Reply
Hide
Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.