Chemistry paper 6 help!

[Jaxine]

http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_s10_qp_61.pdf

The last question!

& for question 6(b), why does crystals change colour from red to blue?

 

[Jaxine]

no replies

 

[mrnt3250]

Cobalt (II) Chloride is a chemical test for water.
Anhydrous CoCl2 is blue while hydrous CoCl2 is purple (pink).
So change from pink to blue means dehydration.

 

[MERIHAN]

can u plz help me with this question 4 f (2)
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_63.pdf

 

[ThatReallyReallyWeirdDude]

can u plz help me with this question 4 f (2)
http://www.xtremepapers.com/papers/CIE/Cambridge IGCSE/Chemistry (0620)/0620_w11_qp_63.pdf

The order is
C A B
The reason is so:
All the sulphuric acid solutions added have the same concentration
The same volumes of C, A and B were used
Only 5.4cm3 of Sulphuric Acid was needed to neutralize 20cm3 of C, meaning C is very dilute (i.e. there weren't alot of moles of sodium hydroxide in 20 cm3 of C)
10.5 cm3 of Sulphuric Acid was needed to neutralize 20cm3 of A- since more H2SO4 is needed this means it's more concentrated/has more moles.
A needed 20.8cm3 of sulphuric acid, meaning it had the most moles of sodium hydroxide and is most concentrated.