Chemistry 3/4 2013 Thread

[teletubbies_95]

Same here dude!:) When we learnt moles in unit 1 , it was the hardest thing in the world , hated it ! I didn't get the point of it ? It was all pointless calcs.  Any 2014rs that hate it , i feel your pain !

But now, it makes sense , because its easier. And i also understand why im doing all this n=cv or n= m/mr!

I guess it takes time

[Mr Keshy]

Same here dude!:) When we learnt moles in unit 1 , it was the hardest thing in the world , hated it ! I didn't get the point of it ? It was all pointless calcs.  Any 2014rs that hate it , i feel your pain !

But now, it makes sense , because its easier. And i also understand why im doing all this n=cv or n= m/mr!

I guess it takes time

Haha, glad I'm not the only one!

[thushan]

Same here dude!:) When we learnt moles in unit 1 , it was the hardest thing in the world , hated it ! I didn't get the point of it ? It was all pointless calcs.  Any 2014rs that hate it , i feel your pain !

But now, it makes sense , because its easier. And i also understand why im doing all this n=cv or n= m/mr!

I guess it takes time

Yup! That's good! Remember - this n=cV and n = m/M is stating the bleeding obvious - once you realise it, it becomes instinctive.

[saba.ay]

Write an unbalanced chemical equation for the reaction between 1-chlorobutane and sodium hydroxide solution.

Now this is the answer I got, and it is right, according to the answers.

CH3CH2CH2CH2Cl  ------( OH- )----> CH3CH2CH2CH2OH

But if I'd written the following, would it have still been right?

CH3CH2CH2CH2Cl  + NaOH ---> CH3CH2CH2CH2OH + NaCl

Please and thanks in advance.

[teletubbies_95]

Write an unbalanced chemical equation for the reaction between 1-chlorobutane and sodium hydroxide solution.

Now this is the answer I got, and it is right, according to the answers.

CH3CH2CH2CH2Cl  ------( OH- )----> CH3CH2CH2CH2OH

But if I'd written the following, would it have still been right?

CH3CH2CH2CH2Cl  + NaOH ---> CH3CH2CH2CH2OH + NaCl

Please and thanks in advance.

So this is a substitution reaction! chlorbutane to sodium hydroxide to make butanol( primary alcohol)
I guess that would be right . NaCl is soluble , so maybe they omitted that it in the equation.
not entirely sure this is right or not ?

[thushan]

So this is a substitution reaction! chlorbutane to sodium hydroxide to make butanol( primary alcohol)
I guess that would be right . NaCl is soluble , so maybe they omitted that it in the equation.

Watch your nomenclature!

1-chlorobutane. butan-1-ol. Best to get into the habit early.

Write an unbalanced chemical equation for the reaction between 1-chlorobutane and sodium hydroxide solution.

Now this is the answer I got, and it is right, according to the answers.

CH3CH2CH2CH2Cl  ------( OH- )----> CH3CH2CH2CH2OH

But if I'd written the following, would it have still been right?

CH3CH2CH2CH2Cl  + NaOH ---> CH3CH2CH2CH2OH + NaCl

Please and thanks in advance.

Your answer is fine; either expressions are just different ways of expressing the same thing. They omitted the NaCl because often when you write the equation in condensed form as the answers did, you only display the organic reagent and product and omit any 'side products' like Cl- ions!

[zvezda]

Na is a spectator ion, so you'd be omitting the Na and writing OH and Cl as ions as the Na doesn't take part in the reaction

[teletubbies_95]

ill do that next time! i was being lazy !

[saba.ay]

Thanks guys. That clears it up.

[Mr Keshy]

Hey guys, I simply do not understand how the first part of this question should be undertaken..

A 2.203 g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32 g of water and the carbon was oxidised to 3.23 g of carbon dioxide.
a)   Find the empirical formula of the compound.

I can easily get the empirical formula bit right. But getting (n), has completely stumped me. I looked at the worked solutions too and that's confused me as well..

Could you please explain to me the steps on how you did it? Thank you

[KevinooBz]

Hey guys, I simply do not understand how the first part of this question should be undertaken..

A 2.203 g sample of an organic compound was extracted from a plant. When it was burned in oxygen, the hydrogen in the compound was converted to 1.32 g of water and the carbon was oxidised to 3.23 g of carbon dioxide.
a)   Find the empirical formula of the compound.

I can easily get the empirical formula bit right. But getting (n), has completely stumped me. I looked at the worked solutions too and that's confused me as well..

Could you please explain to me the steps on how you did it? Thank you

The first part is about the reaction between the elements and compounds. So it says hydrogen is converted into 1.32g of water. We want the mole of the hydrogen so since hydrogen is converted to water, the mole of hydrogen will be two times the mole of the water. So it's 1.32x2/18 which is ~0.1466mol. The second part is that carbon is oxidised to carbon dioxide. One mole of carbon will be equal to one mole of carbon dioxide.so the mole of carbon is just 3.23/44. Then you can find mass and the rest.

[Mr Keshy]

Thanks That makes perfect sense actually. I got really confused with the multiplying by 2 part. I was confused, wondering why we're using information about H₂O to find H.

All solved

[Edward21]

Is anyone else just a little scared for the end of year exam, it's 2.5hrs  that's almost as long as the English exam and both units pulled together on one examination paper 

[Edward21]

On the other hand, this is plain hilarious if you enjoy chemistry and have even the slightest sense of humour 

[teletubbies_95]

I AM SOOO SCARED ! :0. I dont know how to fit all that info in my brain!