# Chemistry: Post your doubts here!

#### Samand

An element X and compound YZ react separately with acid as shown.
X(s) + 2H+(aq) → X2+(aq) + H2(g)
YZ(s) + 2H+(aq) → Y2+(aq) + H2Z(g)
When 1.0 g of either X or YZ is reacted with an excess of acid, the total volume of gas formed is the same.
Which statements are correct?
1. Ar(X) = Mr(YZ)
2. X and Y are metals.
3. X and Y must both be in the same group of the Periodic Table.

Why is the answer "1 and 2 are correct"?

#### coolhudhayfahfaiz

Hi guys, I have a question regarding Fe+2 and KMnO4 titrations. So you do know that before carrying out the titration excess dilute sulfuric acid must be added to the Fe+2 solution to allow redox rxn to occur. But doesn't the addition of excess dilute sulfuric acid(mainly water) dilute the Fe+2 solution in the conical flask?

#### coolhudhayfahfaiz

Re: All Chemistry help here!! Stuck somewhere? Ask here!

A 20.0mL sample of 0.200M HBr solution is titrated with 0.200M NaOH solution. Calculate the pH of the
solution after the following volumes of base have been added:
15 mL
ANYBODY ????

HBr + NaOH -----> NaBr + H20

n=cv=0.02 x 0.2 = 4 x10^-3 moles of HBr

n of NaOH = cv= 0.015 x 0.2= 3 x 10^-3 moles.

1x10^-3 moles of HBr left. Assuming HBr is a strong acid, [H+] = 1x10^-3/0.02+0.015=0.0286 mol dm^-3

ph=-log[H+]=1.54

#### crack the code

Hi guys, I have a question regarding Fe+2 and KMnO4 titrations. So you do know that before carrying out the titration excess dilute sulfuric acid must be added to the Fe+2 solution to allow redox rxn to occur. But doesn't the addition of excess dilute sulfuric acid(mainly water) dilute the Fe+2 solution in the conical flask?
excess dilute acid is added to ensure that the reaction goes to completion only when all of fe2+ ions have been consumed by Mno4- ions and not due to decreased concentration of H+

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#### garyGA

Suggest a test to determine if a MgO substance is mixture or compound. Thank you!

#### Ani876

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

#### 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'