Chemistry: Post your doubts here!

[Xaptor16]

Total removal of the pollutant sulfur dioxide, SO2, is difficult. The quantities emitted from furnace chimneys can be lowered by using desulfurisation plants. The gases are reacted with calcium hydroxide to remove the SO2. What is the main product formed initially?
A Ca(HSO4)2
B CaS
C CaSO3
D CaSO4
help! i don't get how the answer is C? how do you know its not D?
19 Which oxide does not react with cold dilute sodium hydroxide to produce a salt?
A Al 2O3
B P4O10
C SO2
D SiO2
the asnwer is D... i dont understand how!

 

[Xaptor16]

The ester CH3CH2CH2CO2CH3 is responsible for the aroma of apples. When this ester is hydrolysed by acid in the stomach, what is the empirical formula of the organic acid produced?
A CH2O
B CH4O
C C2H4O
D C3H6O2
can someone please explain how its C? wouldnt it be A?

 

[Lola_sweet]

The ester CH3CH2CH2CO2CH3 is responsible for the aroma of apples. When this ester is hydrolysed by acid in the stomach, what is the empirical formula of the organic acid produced?
A CH2O
B CH4O
C C2H4O
D C3H6O2
can someone please explain how its C? wouldnt it be A?

If u draw the structure of A u will see it cant exsist carbon will still ve one empty bond pair or branch left thus it has to be C
I think thts right :/

 

[Nicolle L]

Magnesium nitrate, Mg(NO3)2, will decompose when heated to give a white solid and a mixture of gases. One of the gases released is oxygen. 29.7g of anhydrous magnesium nitrate is heated until no further reaction takes place. What mass of oxygen is produced?
A 3.2g
B 6.4g
C 12.8g
D 19.2g

 

[Xaptor16]

If u draw the structure of A u will see it cant exsist carbon will still ve one empty bond pair or branch left thus it has to be C
I think thts right :/

yes i know, but its the empirical formula we're talking about, it wouldnt make sense to draw the structure out as its not the molecular formula...

 

[Xylferion]

Magnesium nitrate, Mg(NO3)2, will decompose when heated to give a white solid and a mixture of gases. One of the gases released is oxygen. 29.7g of anhydrous magnesium nitrate is heated until no further reaction takes place. What mass of oxygen is produced?
A 3.2g
B 6.4g
C 12.8g
D 19.2g

2Mg(NO3)2 ------> 2MgO + 4NO2 + O2

Mg(NO3)2 = 148 g
Moles of Mg(NO3)2 = 29.7 / 148 =0.201

Ratio is 2 : 1
So 0.1005 moles of O2 formed.
0.1005 moles * 32 g ( Molar mass of O2) = 3.216 g , The answer is A.

Hope that helped

 

[Xylferion]

The ester CH3CH2CH2CO2CH3 is responsible for the aroma of apples. When this ester is hydrolysed by acid in the stomach, what is the empirical formula of the organic acid produced?
A CH2O
B CH4O
C C2H4O
D C3H6O2
can someone please explain how its C? wouldnt it be A?

CH3CH2CH2CO2CH3 undergoes acid hydrolysis in the stomach under the presence of water, with HCl being the acid catalyst of the hydrolysis.

[CH3CH2CH2CO2] comes from the carboxylic acid and CH3 comes from the alcohol. During esterification, OH is taken from the alcohol and H is taken from -COOH in the carboxylic acid.

When hydrolysis takes place, the OH and H are returned to their respective compounds.

So you end up with CH3CH2CH2CO2H for the carboxylic acid and CH3OH for the alcohol.

They're asking for the empirical formula of the acid, so first find out how many carbons, hydrogens and oxygens [CH3CH2CH2CO2H] has.

That is 4 carbons, 8 Hydrogens and 2 oxygens.

C4H8O2 ------> C2H4O, which is why the answer is C.

 

[Xylferion]

Total removal of the pollutant sulfur dioxide, SO2, is difficult. The quantities emitted from furnace chimneys can be lowered by using desulfurisation plants. The gases are reacted with calcium hydroxide to remove the SO2. What is the main product formed initially?
A Ca(HSO4)2
B CaS
C CaSO3
D CaSO4
help! i don't get how the answer is C? how do you know its not D?
19 Which oxide does not react with cold dilute sodium hydroxide to produce a salt?
A Al 2O3
B P4O10
C SO2
D SiO2
the asnwer is D... i dont understand how!

For the first one,
Ca(OH)2 + SO2 -------> CaSO3 + H2O
Ca combines with SO2 ---> CaSO2 and then the extra Oxygen atom comes from (OH)2. The other product is water.

The process mentioned above is known as flue-gas desulfurization. Which is dealing with the waste gases that contain SO2. To be more specific, they use wet scrubbing to get rid of the SO2 in the form of CaSO3 which is solid.

CaSO4 can then be formed by oxidizing CaSO3 so that's probably why CaSO3 takes precedence over CaSO4, in this specific reaction. Though generally it is CaSO3 that you want to have form from the reaction between SO2 and Limestone/lime.

----------------------------------

All of the oxides listed are of period 3 elements. I suggest you have a look through the syllabus content and find out what exactly you must know about period 3 elements besides their trends. You are required to know how their oxides react.

All of the above oxides can react with NaOH. Al2O3 is amphoteric so it can react with both acids and bases.

P4O10, SO2 and SiO2 form acidic oxides that can react with bases. The exception here is that SiO2 only reacts with Hot and concentrated NaOH as opposed to the other 3.

Since the question mentions those that "do not" react with cold dilute NaOH, you can with absolute certainty rule out SiO2 and have that as your final answer.

As for understanding why it does not, I recommend looking into how to determine strong and weak acids/bases. So then you can understand whether dilute/concentrated substances can have an effect on the outcome.

For SiO2, from what I know, its oxide is very weakly acidic and can only be neutralized by strong bases such as NaOH. So a dilute NaOH would not have as much of an effect on SiO2 as a hot and concentrated one would.

Hope that made sense!

 

[The Chill Master]

There's no part f :/

Generally you want to know how many carbons, hydrogens, oxygens if any, are there. Then you want to know what kind of functional groups are present. Accordingly you'll have to arrange the functional groups and the length of the longest chain in order to get what you need.

Sorry I meant Question 4 part f

Thanks a lot for the help...

 

[m7aug]

can anybody please tell me that how that that whether an organic can be made planar by rotating the bonds ? I saw one such question in a P4 may it was 10 may june somewhere i dont remember

 

[a_wiserME!!]

can someone explain why the answer is C?? TIA

 

[Xaptor16]

For the first one,
Ca(OH)2 + SO2 -------> CaSO3 + H2O
Ca combines with SO2 ---> CaSO2 and then the extra Oxygen atom comes from (OH)2. The other product is water.

The process mentioned above is known as flue-gas desulfurization. Which is dealing with the waste gases that contain SO2. To be more specific, they use wet scrubbing to get rid of the SO2 in the form of CaSO3 which is solid.

CaSO4 can then be formed by oxidizing CaSO3 so that's probably why CaSO3 takes precedence over CaSO4, in this specific reaction. Though generally it is CaSO3 that you want to have form from the reaction between SO2 and Limestone/lime.

----------------------------------

All of the oxides listed are of period 3 elements. I suggest you have a look through the syllabus content and find out what exactly you must know about period 3 elements besides their trends. You are required to know how their oxides react.

All of the above oxides can react with NaOH. Al2O3 is amphoteric so it can react with both acids and bases.

P4O10, SO2 and SiO2 form acidic oxides that can react with bases. The exception here is that SiO2 only reacts with Hot and concentrated NaOH as opposed to the other 3.

Since the question mentions those that "do not" react with cold dilute NaOH, you can with absolute certainty rule out SiO2 and have that as your final answer.

As for understanding why it does not, I recommend looking into how to determine strong and weak acids/bases. So then you can understand whether dilute/concentrated substances can have an effect on the outcome.

For SiO2, from what I know, its oxide is very weakly acidic and can only be neutralized by strong bases such as NaOH. So a dilute NaOH would not have as much of an effect on SiO2 as a hot and concentrated one would.

Hope that made sense!

thankyou very much, i really appreciate it that really helps!

 

[Xaptor16]

CH3CH2CH2CO2CH3 undergoes acid hydrolysis in the stomach under the presence of water, with HCl being the acid catalyst of the hydrolysis.

[CH3CH2CH2CO2] comes from the carboxylic acid and CH3 comes from the alcohol. During esterification, OH is taken from the alcohol and H is taken from -COOH in the carboxylic acid.

When hydrolysis takes place, the OH and H are returned to their respective compounds.

So you end up with CH3CH2CH2CO2H for the carboxylic acid and CH3OH for the alcohol.

They're asking for the empirical formula of the acid, so first find out how many carbons, hydrogens and oxygens [CH3CH2CH2CO2H] has.

That is 4 carbons, 8 Hydrogens and 2 oxygens.

C4H8O2 ------> C2H4O, which is why the answer is C.

ugh i was making a stupid mistake i just realized... thank you!

 

[Xylferion]

View attachment 52129

can someone explain why the answer is C?? TIA

Already explained this. It's the first post on this page.

 

[a_wiserME!!]

Already explained this. It's the first post on this page.

k thnk u

 

[a_wiserME!!]

can someone pls answer this???

 

[Xylferion]

View attachment 52135

can someone pls answer this???

The graph represents a two step reaction because of the two dips visible. So from all of those 3 options you need to eliminate the single step reactions.

All of the options presented are of halogenoalkanes under going substitution reactions with NaOH or NH3.

A key factor is the degree of each, that is whether they are primary, secondary or tertiary.

Option 1, the Carbon holding the Halide ion is attached to 3 other carbons, this makes it a tertiary halogenoalkane. These undergo two-step SN1 reactions that are split into a slow stage and then a fast stage.

Option 2, the Carbon holding the Halide ion is attached to 1 other carbon, making it a primary halogenoalkane. These undergo single-step SN2 reactions in which there is a single transition state.

Option 3 is another example of a primary halogenoalkane that will undergo a SN2 reaction.

So from all of the above cases, Option 1 is the only reaction that proceeds under two different stages, a slow and a fast one, which are distinguishable by the steepness of the gradients on the graph.

So your answer will be D.

 

[Xaptor16]

X is a mixture of two compounds of Group II elements. X can undergo thermal decomposition to produce a white solid and only two gaseous products. One of the gaseous products relights a glowing splint. What could be the components of mixture X?
A MgCl 2 and CaCO3
B MgCO3 and Ca(NO3)2
C Mg(NO3)2 and Ca(NO3)2
D MgO and CaSO4
the answer is C... how can you distinguish between all the options and conclude that C is the right one? i suck at periodicity... any advice?

 

[a_wiserME!!]

The graph represents a two step reaction because of the two dips visible. So from all of those 3 options you need to eliminate the single step reactions.

All of the options presented are of halogenoalkanes under going substitution reactions with NaOH or NH3.

A key factor is the degree of each, that is whether they are primary, secondary or tertiary.

Option 1, the Carbon holding the Halide ion is attached to 3 other carbons, this makes it a tertiary halogenoalkane. These undergo two-step SN1 reactions that are split into a slow stage and then a fast stage.

Option 2, the Carbon holding the Halide ion is attached to 1 other carbon, making it a primary halogenoalkane. These undergo single-step SN2 reactions in which there is a single transition state.

Option 3 is another example of a primary halogenoalkane that will undergo a SN2 reaction.

So from all of the above cases, Option 1 is the only reaction that proceeds under two different stages, a slow and a fast one, which are distinguishable by the steepness of the gradients on the graph.

So your answer will be D.

thnx once again

 

[My Name]

Answer is B