# Chemistry: Post your doubts here!

#### Mustfm

X is the oxide of a Period 3 element. X reacts with water to give an acidic solution.
A solution is prepared by reacting 0.100g of X with excess water. This solution was neutralised
by exactly 25.0cm3
of 0.100moldm–3 sodium hydroxide solution.
What could be the identity of X?
A Al 2O3 B MgO C P4O10 D SO3

Need help with this
Acidic oxide of period 3 means its either A, C, D
When so3 is dissolved in water it forms h2so4
H2so4 + 2naoh = na2so4 + 2h2o
note the mole ration of acid to base is 1: 2

Moles of naoh = concentration x volume
0.1 x 25/1000
= 2.5x10^-3
0.100g of x means that if its so3 then
mole = 0.100/16x3 +32
= 1.25x10^-3
which is exactly half
hence ans is D
hope it helps<3

#### Ani876

Acidic oxide of period 3 means its either A, C, D
When so3 is dissolved in water it forms h2so4
H2so4 + 2naoh = na2so4 + 2h2o
note the mole ration of acid to base is 1: 2

Moles of naoh = concentration x volume
0.1 x 25/1000
= 2.5x10^-3
0.100g of x means that if its so3 then
mole = 0.100/16x3 +32
= 1.25x10^-3
which is exactly half
hence ans is D
hope it helps<3
Thank you soo much

#### Leviante

Does anyone know how to do this question, it will be great help if anyone can me understand this question

#### sheraz Malik

https://chat.whatsapp.com/GUVCDHkNyvgDSV1uQljswk ..you’re welcome
Hey, can you send the Group link again? It has been reset I think.

#### Ani876

Compound X contains the elements C, H and O only.
2.00 g of X produces 4.00 g of carbon dioxide and 1.63 g of water when completely combusted.
What is the empirical formula of X?
A CHO2 B C2H2O C C2H4O D CH2O2

#### imlanguages

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#### Justice league 125

Does anyone here have AS chemistry topical past papers?

#### Hmostafa

You need to consider

Fe3+ + e --> Fe2+ E= +0.77
V2+ + 2e --> V

2Fe2+ + V --> 2Fe2+ + V2+

Fe3+ + e --> Fe2+
V3+ + e --> V2+

Fe3+ + V2+ --> V3+ + Fe2+

Fe3+ + e --> Fe2+
VO2+ + 2H+ + e --> V3+ + H2O

Fe3+ + V3+ +H2O --> 2H+ + VO2+ + Fe2+

Now you can see that for the conversion of V to VO2+, you need 4Fe3+ which yield 4Fe2+. Combining the equations, you get this:

4Fe3+ + V3+ H2O --> 2H+ VO2+ + 4Fe2+
which year this question

#### liza123

Hi everyone, AsSalamoAlaikum Wr Wb..

To get things organized in a better way, I am making this thread. As othewise, some queries remain unanswered!

Any Chemistry related notes and links will be added here in this post. Feel free to provide the links to your notes around the forum, or any other websites!

Chemistry Notes:

http://www.chemguide.co.uk This is the website, which contains almost everything classified according to the syllabus.

Tips for solving chemistry MCQs 9701/01

Chemistry P5 Tips and Notes

Some links & Notes - by 'destined007'

Chemistry worksheets Link shared by hassam

Chemistry Application Booklet: Mistakes and Corrections!

Calculations for A level Chemistry, author E.N. Ramsden third edition ebook download.

Regards,
XPC Staff.
Can any one plz send me the chapter end questions and answers of As and A level chemistry 3rd edition?

9701/51/m/j/ 21
Ques2...d(iv)

#### Nagham Ghandour

Anyone has a file that consists of the hardest AS level questions of paper 2'