Chemistry: Post your doubts here!

[ptet.chemistry]

i have attached two files here: a question paper and its markscheme. Please do help me with number 6b as soon as possible. Why 19.10 (which I think is got directly from the titre of titration 5). Why not sum up all titre values then divide by 5, I had got 19.23? How am I calculating wrong, or where am I not understanding the question?

If you had done any A Level titrations, you should be aware of what concordant titres within +/-0.10 cm3 is the maximum acceptable. You are going to be marked within that margin relative to that of your teacher/centre supervisor who has to do the titration using the same batch of chemicals you did, and that is how titration accuracy marks are marked. Looking at the five readings, you should be able to see that reading 1 is comparatively different from the others. I didn't check all the titres, I just quickly glanced over them, so you get to them again.

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[Bobo17]

NOVEMBER 2015 P11 QUESTION 16

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 0.100 moldm–3 sodium hydroxide solution.

What could be the identity of X?
A A l2O3
B MgO
C P 4O10
D SO3


Can anyone explain why answer is D?

 

[kent123]

hi. so3 + 2naoh ->na2so4 + h2o
mol of NaOH = 2.5 x 10^-3 mol = 2 x mol of SO2
mol of SO2 = 1.25 x 10-3 mol
Mr of X oxide = mass / mol = 0.1 / 1.25x10^-3 = 80 g/mol

SO3 is (3 x 16) + 32 = 80 g/mol

i did this backwards, knowing the answer as you've told. u can do it forwards by writing down each balanced equations and see which one fits.

 

[Jawahir Ghafoor]

here, can somebody explain me question 16 part (c) ??
the markscheme answer is pentane.

 

[Hamnah Zahoor]

here, can somebody explain me question 16 part (c) ??
the markscheme answer is pentane.

i wasn't able to find even a clue
I guess the question was wrong because as according to the above equation none of the options are correct. Is this a whole question from a paper? if yes please mention the year and variant.
if this is your school exam they might have mixed the question options

 

[FahimJustFahim]

View attachment 64351 Can anyone solve this, please?

its B

View attachment 64351 Can anyone solve this, please?

Its B

 

[tahmed.troy]

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 25.0 cm of 0.100 mol dm sodium hydroxide solution.
what could be the identity of X?
Al2O3
MgO
P4O10
SO3

 

[ptet.chemistry]

Hi guys, so about half a year ago, when I was writing up my thesis, I was inspired to start my own Chemistry tutorial channel. It has since humbly continued to attract more viewers (students/learners, I assume) globally.

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It is not a fancy channel, but an educational one at best. In my previous work, I was (and still am!) an accomplished synthetic organometallic chemist, working with some of the most air-sensitive compounds. My passion is however in advancing chemical education and affording equal opportunities for all who want to learn from me.

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[Zenchin92]

Hi can someone help me with this question ?

 

[ptet.chemistry]

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[Scoobydoo435]

hi i wanted to ask something relating to electronegativity. In the syllabus it says understand, in simple terms, the concept of electronegativity and apply it to explain the properties of molecules such as bond polarity (see also Section 3.3(c)), the dipole moments of molecules (3.3(d)) and the behaviour of oxides with water. How can i apply the concept to the behaviour of oxides?

More electronegative the central metal atom, more acidic the oxide

 

[blootoomatoo]

P×7000×10*-6=0.96/32×8.31×303


Ans:10.8 kPa

So it's C

Why do you multiply 7000 by 10*-6?

 

[Tasneem Ayham]

Hello Everyone!
Can anyone help me with this? How is it B? How do I solve such equations?

 

[MUGABE King]

OK so first you need to know the reactions of the period 3 oxides with water. AL2O3 does not react so optionA b are wrong. Next we react 2NaOH (which is a basic oxide and the product of reaction between oxide and H2O) with corresponding acidic oxide & balance the equations.
NOTE The Q states"neutralised by exactly 1mol....so D is correct as it balances perfectly with 2NaOH.

thank you

 

[crack the code]

Hello Everyone!
Can anyone help me with this? How is it B? How do I solve such equations?View attachment 66150

what year is this q from?

 

[reinemiraa]

The lattice energies(enthalpies) of rubidium fluoride(RbF) and caesium chloride(CsCl) are -760 KJ/mol and -650kJ/mol respectively. What is the lattice energy of caesium Fluoride(CsF) likely to be? (Rb-37;Cs-55) ANS B
A.-620kJ/mol
B.-720 kJ/mol
C.-800kJ/mol
D.-900kJ/mol
can any1 explain n is this an AS question?

hi , can i know you get B ?

 

[reinemiraa]

The lattice energies(enthalpies) of rubidium fluoride(RbF) and caesium chloride(CsCl) are -760 KJ/mol and -650kJ/mol respectively. What is the lattice energy of caesium Fluoride(CsF) likely to be? (Rb-37;Cs-55) ANS B
A.-620kJ/mol
B.-720 kJ/mol
C.-800kJ/mol
D.-900kJ/mol
can any1 explain n is this an AS question?

do you know the explanation?

 

[reinemiraa]

The lattice energies(enthalpies) of rubidium fluoride(RbF) and caesium chloride(CsCl) are -760 KJ/mol and -650kJ/mol respectively. What is the lattice energy of caesium Fluoride(CsF) likely to be? (Rb-37;Cs-55) ANS B
A.-620kJ/mol
B.-720 kJ/mol
C.-800kJ/mol
D.-900kJ/mol
can any1 explain how the answer is B

 

[astro04]

does anyone know what is the corresponding letters options for questions like this

When organic refuse decomposes in water carboxylic acids are formed. The water becomes acidic and aquatic life is destroyed.
Which additives are suitable to remove this acid pollution?
1 calcium carbonate
2 calcium hydroxide
3 potassium nitrate

The answer is B. Which options is it referring to?

 

[crack the code]

does anyone know what is the corresponding letters options for questions like this

When organic refuse decomposes in water carboxylic acids are formed. The water becomes acidic and aquatic life is destroyed.
Which additives are suitable to remove this acid pollution?
1 calcium carbonate
2 calcium hydroxide
3 potassium nitrate

The answer is B. Which options is it referring to?

option 1 and 2