[Professor]

1) Phosphorus is in the same group of the Periodic Table as nitrogen. What is the most likely molecular formula of a hydride of phosphorus?

Ans: PH3 (I don't understand why the answer is this...Please explain to me...Thanks.)


2) Crystals (be it any crystals) are all pure, right?


3) Eqn 1: H2 ---> 2H
    Eqn 2: HCl ---> H + Cl
    Eqn 3: 2H + O ---> H2O

The answer states that eqn 1 & 2 are endothermic processes. Why? I don't understand...Can explain? Thanks...


4) Why diluting concentrated sulphuric acis is an endothermic process? Is it because during the process heat is taken in? But I don't understand..Does diluting concentrated sulphuric acid means that the acid is being diluted by adding in more concentrated sulphuric acid?


5) Are all solutions and precipitates considered salts? Or if not, are only some of the solutions and precipitates are considered as salt depending on their solubility in water?


6) The labels fell off 2 bottles. One bottle was known to contain sodium carbonate, and the other sodium chloride solution. Which of the following tests would most easily identify the solutions?

a) Addition of aqueous ammonia
b) Addition of blue litmus paper
c) Addition of dilute sulphuric acid
d) Addition of lead(II) nitrate solution.

The answer for this question is (c) adding of dilute sulphuric acid. Can someone explain to me why adding of sulphuric acid will most easily identify the solutions? Thanks so much. 


Please help me explain all, if not, any of the above 6 questions...My mid-year is coming soon so I would really need to clear my doubts on these questions..Thank you.

[Borek]

Please read forum rules. Black reads much better then red.

[MJA]

It depends on how the crystals are formed.

[UnintentionalChaos]

Here are a few questions in response to your questions. Think about it and the reasons shall become obvious.

1.What do the groups have in common? What is nitrogen hydride?

2.Ever heard of semiconductor doping?

3. Why do molecules exist?

4.I think it should say exothermic.

5. Are salts the only things soluble in water? Single replacement reaction anyone?

6. Go look up possible reaction products and think about it.