Chemistry: Post your doubts here!

[sharjilali90]

A2 chemistry O/N 11, variant 43
"Calculate the pH of the buffer formed when 10.0 cm3 of 0.100 mol dm–3 NaOH is added to 10.0 cm3 of 0.250 mol dm–3 CH3CO2H, whose pKa = 4.76"
How do I solve this?

 

[Thought blocker]

A2 chemistry O/N 11, variant 43
"Calculate the pH of the buffer formed when 10.0 cm3 of 0.100 mol dm–3 NaOH is added to 10.0 cm3 of 0.250 mol dm–3 CH3CO2H, whose pKa = 4.76"
How do I solve this?
View attachment 61150

https://www.xtremepapers.com/commun...st-your-doubts-here.9859/page-371#post-736866

 

[drowning-in-studies]

36 Ammonia and chlorine react in the gas phase.
8NH3 + 3Cl 2 → N2 + 6NH4Cl
Which statements are correct?
1 Ammonia behaves as a reducing agent.
2 Ammonia behaves as a base.
3 The oxidation number of the hydrogen changes.
The answer is B
I don't understand why 3 is false. Doesn't H change from +3 to +4??

 

[Thought blocker]

36 Ammonia and chlorine react in the gas phase.
8NH3 + 3Cl 2 → N2 + 6NH4Cl
Which statements are correct?
1 Ammonia behaves as a reducing agent.
2 Ammonia behaves as a base.
3 The oxidation number of the hydrogen changes.
The answer is B
I don't understand why 3 is false. Doesn't H change from +3 to +4??

oxidation number of hydrogen is +1.
There are 3 hydrogen molecules so we multiply 3 with +1 and so with 4 molecules of hydrogen 4(+1)
So oxidation number is unchanged of hydrogen

 

[drowning-in-studies]

oxidation number of hydrogen is +1.
There are 3 hydrogen molecules so we multiply 3 with +1 and so with 4 molecules of hydrogen 4(+1)
So oxidation number is unchanged of hydrogen

Ahh...I see Thanks

 

[kungfuPanda]

Hi guys Ive simple question,Are we allowed to explain terms like e.g orbital hybridization or something like this ..I mean definitions?
Will we be awarded marks or no marks if we explain or not explain definitions?

2nd quetsion is are marks only awarded for what a question seeks in terms of our broad understanding or are they predefined and restricted in the marks sheets? like award this 1 marks and award this 2 marks or one or whatever?
linkinpark help me out bro

 

[Thought blocker]

Hi guys Ive simple question,Are we allowed to explain terms like e.g orbital hybridization or something like this ..I mean definitions?
Will we be awarded marks or no marks if we explain or not explain definitions?

2nd quetsion is are marks only awarded for what a question seeks in terms of our broad understanding or are they predefined and restricted in the marks sheets? like award this 1 marks and award this 2 marks or one or whatever?
linkinpark help me out bro

If u are learning CIE, till I know, i didnt come across any different things, may be if u learned some other board and appearing CIE A levels, till i know they do accept, as this is what sir said to me, thought its not in ms, but answers equivallent is considered.

Wait for others to reply u.

 

[kungfuPanda]

If u are learning CIE, till I know, i didnt come across any different things, may be if u learned some other board and appearing CIE A levels, till i know they do accept, as this is what sir said to me, thought its not in ms, but answers equivallent is considered.

Wait for others to reply u.

Yup Cie it is,btw dudee this site is totally dead :3

 

[drowning-in-studies]

How do you solve this?? Do you just add?
Can someone pls explain each statement?
The ans is D

 

[Thought blocker]

Yup Cie it is,btw dudee this site is totally dead :3

Agreed!

 

[Thought blocker]

How do you solve this?? Do you just add?
Can someone pls explain each statement?
The ans is D

Just follow the direction.
1. U to S + S to R = U to R = -92 + 134 = 42
2. T to S = T to U + U to S = -75 - 92 = exothermic.
3. R to T = R to S + S to U + U to T = -134 + 92 + 75 = 33.

Only 1 is correct. THus D.

 

[drowning-in-studies]

Just follow the direction.
1. U to S + S to R = U to R = -92 + 134 = 42
2. T to S = T to U + U to S = -75 - 92 = exothermic.
3. R to T = R to S + S to U + U to T = -134 + 92 + 75 = 33.

Only 1 is correct. THus D.

But how do you decide when to add and subtract? Is it in reference to where the arrows are pointing? What am i missing out?
like, -75+92 or -75-92?

 

[Thought blocker]

But how do you decide when to add and subtract? Is it in reference to where the arrows are pointing? What am i missing out?
like, -75+92 or -75-92?

Yes by looking at arrow.
It took 92 energy from s to u, so -92 from u to s. Get it?

 

[Bah...]

Hello, can somebody please help me solve these questions?







Thanks in advance.

 

[Saad the Paki]

Hello, can somebody please help me solve these questions?

View attachment 61171

View attachment 61172

View attachment 61173

Thanks in advance.

For the first question:

10cm3 of CS2 will burn in 30cm2 of O2 to give 10 cm3 of CO2 and 20 cm3 of SO2 (basic stoichiometry) . But we have 50cm3 of O2 which means it's an excess. 50-30=20cm3 of excess O2. So after burning out total volume will be :
10cm3 of CO2 + 20cm3 of SO2 + 20cm3 of leftover O2 = 50cm3 of gas.
When these gases are passed through NaOH which is basic, it will react with acidic gases and absorb them
CO2 and SO2 are acidic whereas O2 is neutral. So NaOH will absorb 10cm3 of CO2 + 20cm3 of SO2= 30cm3 absorbed. So leftover volume will be Total-absorbed = 50-30= 20cm3. Which makes option C correct.

 

[Thought blocker]

Hello, can somebody please help me solve these questions?

View attachment 61171

View attachment 61172

View attachment 61173

Thanks in advance.

 

[Bah...]

For the first question:

10cm3 of CS2 will burn in 30cm2 of O2 to give 10 cm3 of CO2 and 20 cm3 of SO2 (basic stoichiometry) . But we have 50cm3 of O2 which means it's an excess. 50-30=20cm3 of excess O2. So after burning out total volume will be :
10cm3 of CO2 + 20cm3 of SO2 + 20cm3 of leftover O2 = 50cm3 of gas.
When these gases are passed through NaOH which is basic, it will react with acidic gases and absorb them
CO2 and SO2 are acidic whereas O2 is neutral. So NaOH will absorb 10cm3 of CO2 + 20cm3 of SO2= 30cm3 absorbed. So leftover volume will be Total-absorbed = 50-30= 20cm3. Which makes option C correct.

Thank you!

 

[Bah...]

Thank you!

 

[Rameen19]

Chemistry periodicity, group 2 & group 17 equations.. How do we memorize so many? Advice would be appreciated thankyou

 

[Atharxd1]

Hey everybody i'm new around here. In currently in AS after failing first year IB (sad story, but it is the story). Now i'm stuck in one AS question:

Ferrochrome is an alloy of iron and chromium. Ferrochrome can be dissolved in dilute sulfuric acid to produce a mixture of FeSO4 and Cr2(SO4)3. The FeSO4 reacts with K2Cr2O7 in acid solution according to the following equation. 14H+ + 6Fe2+ + Cr2O72– → 2Cr3+ + 6Fe3+ + 7H2O When 1.00 g of ferrochrome is dissolved in dilute sulfuric acid, and the resulting solution titrated, 13.1 cm3 of 0.100 mol dm–3 K2Cr2O7 is required for complete reaction. What is the percentage by mass of Fe in the sample of ferrochrome?

A 1.22
B 4.39
C 12.2
D 43.9
Could anyone explain to me with steps, also showing the working to get to the final answer, THANKS!