Chemistry MCQ's help!

[scouserlfc]

Here is a proof that lesco1995 is right.

http://www.gcsescience.com/itestchlorinegas.htm

 

[bikermicefrmars]

Thankx everyone now what about the question I posted on last page?

 

[scouserlfc]

Another One:

Q A student tested a solution by adding aqueous sodium hydroxide. A precipitate was not seen
because the reagent was added too quickly.
What could not have been present in the solution?
A Al3+ B Ca2+ C NH4+ D Zn2+

Shouldn't the answer NH4+?

Yes exactly it is NH4+ because it does not react with NaOH and there is no reaction.Refer to the Salt Analysis stuff in the syllabus or somewhere in your redspot past papers or in presscots book well this is the correct answer,

 

[bikermicefrmars]

@scouserlfc....in the marking scheme it is written Ca2+.

 

[scouserlfc]

Which Question can i have the year

 

[bikermicefrmars]

I dun remember the year...but I am telling u that it was Ca2+

Another question here:

Q When added to 20 cm3 of 0.5 M sulphuric acid, which substance would give a neutral solution?
A 20 cm3 of 0.5 M sodium hydroxide
B 10 cm3 of 0.5 M sodium hydroxide
C 40 cm3 of 1.0 M sodium hydroxide
D 20 cm3 of 1.0 M sodium hydroxide

How will we arrive to it;s answer?

 

[scouserlfc]

Answer would be D i think and ill check that Ca2+ question

 

[bikermicefrmars]

How is it D?

 

[scouserlfc]

You must remember that there are 2 H here so they will require double the amount of NaOH and if you try to make an equation you will see that it balnces only when 2 NaOH are there,

2 NaOH + H2SO4 > 2H2O + Na2SO4 ... . . . . . .

Hope u understood.

As the mole of one NaOH is 0.5 mole.

 

[bikermicefrmars]

I understood....thanks!

 

[scouserlfc]

okay ill check the Ca 2+ ion

 

[abcde]

Another One:

Q A student tested a solution by adding aqueous sodium hydroxide. A precipitate was not seen
because the reagent was added too quickly.
What could not have been present in the solution?
A Al3+ B Ca2+ C NH4+ D Zn2+

Shouldn't the answer be NH4+?

Yes, it is Ca+2. You see, when they say the reagent was added too quickly, they mean it was in excess. Al3+ and Zn2+ are soluble in excess so they could be present in the solution. NH4+ could also be present as it does not produce a ppt. However, the ppt produced by calcium ions is insoluble in excess so it could NOT be present as a ppt would be seen EVEN IF the reagent is added too quickly! Get it?

 

[bikermicefrmars]

@abcde...thanks!

 

[bikermicefrmars]

Another one:

QCaesium, Cs, is an element in Group I of the Periodic Table.
Which statements about Caesium are true?
1 Caesium conducts electricity both when solid and when molten.
2 Caesium reacts explosively with water.
3 Caesium reacts with water and forms a solution of pH < 7.
A 1 and 2 only
B 1 and 3 only
C 2 and 3 only
D 1, 2 and 3

What is the answer in ur opinion guys?

This one as well:

Q A sample of hydrogen is a mixture of the two isotopes H 1
1 and H 2

The relative atomic mass of oxygen is 16.
What are possible values of the relative molecular mass of different molecules of water formed by
the combination of oxygen and hydrogen?
1 18
2 19
3 20
A 1 only
B 1 and 2 only
C 1 and 3 only
D 1, 2 and 3

And how will we calculate this:

32 What is the concentration of hydrogen ions in 0.05 mol / dm3 sulfuric acid?
A 0.025 g / dm3
B 0.05 g / dm3
C 0.10 g / dm3
D 2.0 g / dm3

THanks!

 

[abcde]

There is really a 'thanks button' for thanking! You know that?

 

[bikermicefrmars]

Thanked.....plz answer the three questions above?

 

[abcde]

For the caesium one, it's A. For the hydrogen one it's D because these are the possibilities for calculating Mr : 16 + 1 + 1 = 18, 16 + 1 + 2 = 19, and 16 + 2 + 2 = 20. I hope you got what I did. The conc. of hydrogen ions is C.

 

[abcde]

So? Got it?

 

[bikermicefrmars]

THe first one in marking scheme is B dont know why>?

And didnt get the last one?

 

[abcde]

1 mol of sulphuric acid contains 2 moles of hydrogen ions so 0.05 mol would contain (0.05 x 2) = 0.1 mol of hydrogen ions. The Ar of hydrogen is 1 so conc. = 0.1 x 1= 0.1 g/dm3.