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secondary 4 | A Maths
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need help with these qns, pls explain too
Date Posted: 3 years ago
Views: 317
26 is calcium. It’s the only cation in the list which gives a white precipitate even when lots of sodium hydroxide is added to try and dissolve the precipitate.
Y is metal. Z is non metal.
Y is surrounded by eight Z.
Z is surrounded by four Y.
It’s practically a way to say that there are twice as many Z atoms as Y (how else can each Y see so many Z?)
To balance these, the charge on Y must be double that of the charge on Z.
Y has charge +2.
Z has charge -1.
Compound formula is YZ2. This is also an indication that there are two atoms of Z for every one atom of Y.
Y is surrounded by eight Z.
Z is surrounded by four Y.
It’s practically a way to say that there are twice as many Z atoms as Y (how else can each Y see so many Z?)
To balance these, the charge on Y must be double that of the charge on Z.
Y has charge +2.
Z has charge -1.
Compound formula is YZ2. This is also an indication that there are two atoms of Z for every one atom of Y.
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For Q26 I feel that Ca2+ would be better, since it gives a white precipitate which fails to dissolve in excess NaOH.
In other words, because Ca2+ is going to give a white precipitate either way, it could not have been present in the solution.
Zinc, lead and ammonium might be present because they lead to colourless solutions when excess sodium hydroxide is added to any of them.
In other words, because Ca2+ is going to give a white precipitate either way, it could not have been present in the solution.
Zinc, lead and ammonium might be present because they lead to colourless solutions when excess sodium hydroxide is added to any of them.
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