Chemistry: Post your doubts here!

[blymphocytes]

I mean I don’t really know , I’m just really lost

Yea.....-160 is correct
After that it's not much of a hustle.....use hess law to equate enthalpy change of sol, lattice energy and hydration energy
your eqn will be -2526-160=2x-1890
X in this case is cl ions....and since 2 are need to form mgcl2 so 2x

 

[student3737]

Guys how do you find the order for H?

 

[blymphocytes]

Guys how do you find the order for H?

Is it zero?

 

[student3737]

Is it zero?

It’s one

 

[blymphocytes]

It’s one

omg how noww??

 

[blymphocytes]

omg how noww??

Its fine i got it....the ratio between expt 2 and 3

 

[oalevel2020]

9701/42/M/J/17 Q3(b)(iii)
Calculate the number of moles of RCO2H that produced the SO2 and HCl.
In neutralising SO2 with NaOH, two moles of NaOH were needed for each mole of SO2. So should it affect the mole ratio of RCO2H : NaOH when calculating the number of moles of RCO2H that produced the SO2 and HCl?
Jaldi batao, I need the answer, please.

 

[oalevel2020]

In the nucleophilic addition of HCN to C=O, what should be the conditions and reagents?
For the reagents, should we write NaCN and dilute H2SO4 or should we write HCN + NaCN as written in the mark scheme of 9701/42/M/J/17 Q8 (a)(iii) Step-2?

 

[oalevel2020]

9701/41/M/J/17 Q6(d)(i)
In the Proton NMR spectrum of 1-phenyl-ethan-1-ol, C6H5CH(OH)CH3 would the -CH- have a peak at 2.7 ppm or at 4.1 ppm?
In this compound -CH- is bonded to an aromatic ring at one end and to an electronegative O atom at the other end. So if -CH- is considered as an alkyl next to aromatic ring, it can have a peak at delta value of 2.7 ppm.
But if -CH- is considered as an alkyl next to electronegative atom it can have a peak at delta value of 4.0 ppm.
So what should be the correct option?
Please please help me!

 

[oalevel2020]

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


jaldi btao....i calculated bt not confident wid ma anser

n(KOH) = 0.001 mol; n(CH3COOH)=0.01025 mol. They react in 1:1 ratio, so after neutralisation moles of ethanoic acid left = 0.01025 - 0.001=0.00925 mol.
So [ethanoic acid] = 1000*0.00925/35 = 0.2643 mol/dm3. After reaction, moles of CH3COOK produced is 0.001 mol. So [CH3COOK] = 1000*0.001/35 = 0.02857 mol/dm3.
So pH = pKa + log ([Salt]/[acid]) = -log(1.74*10^-5) + log (0.02857/0.2643) = 3.79 (Ans)

 

[Kanekii]

Need help with this also the ans is 21:9

 

[Ebrahim12]

Need help with this also the ans is 21:9View attachment 64677

If the molecule only had one primary and one tertiary H atoms, the ratio would be 21:1, but since there are 9 primary H atoms for every one tertiary, that increases its relative rate by 9 times, 21:9.

 

[Kanekii]

If the molecule only had one primary and one tertiary H atoms, the ratio would be 21:1, but since there are 9 primary H atoms for every one tertiary, that increases its relative rate by 9 times, 21:9.

Oh Thank you!!

 

[student3737]

When oxidized by KMNO4 what are the three products formed from abscisic acid , ?

 

[blymphocytes]

Hy Guys,
Can anyone tell me the observations of 2,4,6 tribromophenol and 2,4,6 tribromophenylamine
I tend to confuse the 2.

 

[oalevel2020]

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

http://www.xtremepapers.com/CIE/Interna ... 4_qp_1.pdf
q. 20 and 26

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



I am going to give it a try.

Moles HBr = 0.020 L x 0.200 M =0.0040
Moles NaOH = 0.015 L x 0.200 =0.0030

Moles H+ in excess = 0.0010
Total volume = 0.015 L
Concentration H+ = 0.0010 / 0.015 =0.0667
pH =-log ( 0.06667)
=0.176

--------------------------------------------------------------------------------------------------------------------
I think there is a mistake in the above answer:
The total volume will be 0.035 L (0.02 L + 0.015 L)
Concentration of H+ = 0.0010/0.035 = 0.02857 M
pH = -log (0.02857) = 1.54 (Ans)

 

[mittul8yu98]

9701/41/M/J/17 Q6(d)(i)
In the Proton NMR spectrum of 1-phenyl-ethan-1-ol, C6H5CH(OH)CH3 would the -CH- have a peak at 2.7 ppm or at 4.1 ppm?
In this compound -CH- is bonded to an aromatic ring at one end and to an electronegative O atom at the other end. So if -CH- is considered as an alkyl next to aromatic ring, it can have a peak at delta value of 2.7 ppm.
But if -CH- is considered as an alkyl next to electronegative atom it can have a peak at delta value of 4.0 ppm.
So what should be the correct option?
Please please help me!

to be honest this question is very confusing.
ch is next to electronegetive atom and also next to aromatic ring so ithas higher ppm

 

[mittul8yu98]

help ASAP

 

[Kashintha]

Anyone have an idea about the practical test this time 2019?

 

[sukasukinya]

help ASAP

What is the answer?