[Xenonman]

I am doubtful, yet again. I found these questions a while ago. I didn't bother then but I know it's time to ask CF about 'em.

Q1: When half a mole of K₂CrO₄ and one mole of Ag₂NO₃ are mixed in a liter of water:
(The Ag⁺ ions are enough to sink all the CrO₄^2-, so the correct statement is: )
Solution remains colorless, and a red ppt is formed.

Q2: When a mole of K₂CrO₄ and one mole of Ag₂NO₃ are mixed in a liter of water:
(Not enough Ag⁺ to sink the CrO₄^2-, so: )
A2: Solution becomes yellow, a red ppt is formed.

Q3: A solution of a pH=7.2 is:

a) Slightly basic

b) Neutral

c, d, e) Other nonsense

I am confused in this one. A basic chem book I had, those that give pH of substances without stating the importance of concentration and water as solvent, said the neutrality range is in between 6 and 8. Time passed and I learned about K_w and why pure water at STP is supposed to be purefectly neutral.

I suppose this one is somewhat subjective, and the so-called correct answer depends on the one that asks.

[Borek]

I would go with slightly basic.

[Xenonman]

 
Just noticed this thread is not related to coprecipitation. Yet I named it as if it was.
Just noticed I wrote silver(II) nitrate.

On a happier hand, slightly basic was the correct one.

[Big-Daddy]

Q2: When a mole of K₂CrO₄ and one mole of Ag₂NO₃ are mixed in a liter of water:
(Not enough Ag⁺ to sink the CrO₄^2-, so: )
A2: Solution becomes yellow, a red ppt is formed.

Why is there not enough Ag⁺ to sink the chromate? One mole of Ag₂NO₃  2 moles of Ag⁺ in solution, which is exactly what you need to precipitate out 1 mol of chromate as Ag₂CrO₄.

If you want to go the way of arguing by non-0 solubility product, then that will apply in the first case too - there will surely be some chromate left behind every time!

[Xenonman]

This is just embarassing. First I write "Ag₂NO₃", which is not supposed to exist. Later on, I say I mistakenly wrote "Ag₂CrO₄". That one salt is actually correct.

Should you add actual silver(I) nitrate, Ag₁(NO₃)₁, you'd sink only half of the chromate ions.
If you actually used the "Ag₂NO₃" thing, you'd end up sinking pretty much all of the chromate and silver ions. The only problem is the nonexistence of that salt. Only way to get some is having a typo while trying to write AgNO₃

[Big-Daddy]

This is just embarassing. First I write "Ag₂NO₃", which is not supposed to exist. Later on, I say I mistakenly wrote "Ag₂CrO₄". That one salt is actually correct.

Should you add actual silver(I) nitrate, Ag₁(NO₃)₁, you'd sink only half of the chromate ions.
If you actually used the "Ag₂NO₃" thing, you'd end up sinking pretty much all of the chromate and silver ions. The only problem is the nonexistence of that salt. Only way to get some is having a typo while trying to write AgNO₃

How the **** I missed that and just proceeded with an explanation taking Ag₂NO₃ as a real salt, I will never be able to explain.