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Sameee......i'm not even confident about my answers
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Chemistry: Post your doubts here!
- Thread starter XPFMember
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Most of them from 1 to 20 were C and 21-40 were A :O
I did 12, and it was horrible as well.
The questions needed alot of time, and most questions were organic.
If we had more time I'd say it was good.
I had no time to check I just answered.
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Q: Equal masses of barium carbonate and magnesium carbonate powders are mixed together. The mixture is then heated using a Bunsen burner flame until there is no further change. A gas is given off. Which statements are correct?
1) The residue left after heating reacts with aqueous hydrochloric acid to produce carbon dioxide.
2) The percentage decrease in mass after heating is 26% (to 2 significant figures).
3) The gas given off during heating relights a glowing splint.
1. The fact that some carbon dioxde is produced when the residue is treated with acid means that there is a carbonate present.
2. If 50% of the mixture is magnesium carbonate (relative mass = 84) and it decomposes to MgO (relative mass 40), then the 50% loses 44/84 x 100 % of its mass = 52.4%
so the mass loss of the 100% mixture = 26.2%( dont get this part)
How from 52.4 become 26.2?
1) The residue left after heating reacts with aqueous hydrochloric acid to produce carbon dioxide.
2) The percentage decrease in mass after heating is 26% (to 2 significant figures).
3) The gas given off during heating relights a glowing splint.
1. The fact that some carbon dioxde is produced when the residue is treated with acid means that there is a carbonate present.
2. If 50% of the mixture is magnesium carbonate (relative mass = 84) and it decomposes to MgO (relative mass 40), then the 50% loses 44/84 x 100 % of its mass = 52.4%
so the mass loss of the 100% mixture = 26.2%( dont get this part)
How from 52.4 become 26.2?
In this case, the answer must be D.
Since they mentioned bunsen burner, we know that MgCO3 is the one that went through decomposition, not barium compound since as you go down the group heir thermal stability increases and will require more energy that a burner cannot provide. The residue left is BaCO3 which will obv react with HCl to give out CO2.
For option 2, you are right, % decrease, in this case, is 52.19.. and not 26% therefore option 2 is wrong. You calculate % decrease by (original-final/original)*100.
3 is obviously wrong. I am assuming you also answered D!
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Ethanal, CH3CHO, can be reduced using an aqueous methanolic solution of NaBH4, as the reducing agent.
This is a nucleophilic addition reaction.
What could be the first step of this mechanism?
A) attack of an H+ ion at the carbon atom of the carbonyl group
B) attack of an H+ ion at the oxygen atom of the carbonyl group
C) attack of an H- ion at the carbon atom of the carbonyl group
D) attack of an H- ion at the oxygen atom of the carbonyl group
Can someone explain why the ans is C?
This is a nucleophilic addition reaction.
What could be the first step of this mechanism?
A) attack of an H+ ion at the carbon atom of the carbonyl group
B) attack of an H+ ion at the oxygen atom of the carbonyl group
C) attack of an H- ion at the carbon atom of the carbonyl group
D) attack of an H- ion at the oxygen atom of the carbonyl group
Can someone explain why the ans is C?
Hey guys, A level electrolysis question up ahead-
the question is on the right and the mark scheme on the left. According to my calculations, 1519.685 C of charge was used and therefore time = 1519.685/0.5 which is also what they said. My answer is, however, t=3039 seconds and NOT 5034 seconds. So is the mark scheme wrong in this case? or is there something that I am overlooking?
the question is on the right and the mark scheme on the left. According to my calculations, 1519.685 C of charge was used and therefore time = 1519.685/0.5 which is also what they said. My answer is, however, t=3039 seconds and NOT 5034 seconds. So is the mark scheme wrong in this case? or is there something that I am overlooking?
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I know this was asked like 6 years ago but i dont understand the explanations so im hoping this time round i can get it
Ques: Two moles of compound P were placed in a vessel. The vessel was heated and compound P
was partly decomposed to produce Q and R. A dynamic equilibrium between chemicals P, Q and
R was established.
At equilibrium x moles of R were present and the total number of moles present was (2 +2/x ).
What is the equation for this equilibrium reaction? [Key: --> is the equilibrium sign]
A P --> 2Q + R
B 2P --> 2Q + R
C 2P --> Q + R
D 2P --> Q + 2R
Ques: Two moles of compound P were placed in a vessel. The vessel was heated and compound P
was partly decomposed to produce Q and R. A dynamic equilibrium between chemicals P, Q and
R was established.
At equilibrium x moles of R were present and the total number of moles present was (2 +2/x ).
What is the equation for this equilibrium reaction? [Key: --> is the equilibrium sign]
A P --> 2Q + R
B 2P --> 2Q + R
C 2P --> Q + R
D 2P --> Q + 2R
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pls guys post predictions under here
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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?
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?
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W17 qp11 question 17
71.0 g of chlorine, Cl 2, react with an excess of sodium hydroxide solution at a particular temperature. The reaction produces exactly 35.5 g of product X.
What is product X?
A H 2O
B NaCl
C NaCl O
D NaCl O3
Can someone explain this
71.0 g of chlorine, Cl 2, react with an excess of sodium hydroxide solution at a particular temperature. The reaction produces exactly 35.5 g of product X.
What is product X?
A H 2O
B NaCl
C NaCl O
D NaCl O3
Can someone explain this
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Which of the following solids contain more than one type of chemical bond?
1)brass( an alloy of copper and zinc)
2)graphite
3)ice
1)brass( an alloy of copper and zinc)
2)graphite
3)ice
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Q8) Use of the Data Booklet is relevant to this question.
The approximate percentage composition of the atmosphere on four different planets is given in
the table below.
The density of a gas may be defined as the mass of 1 dm3
of the gas measured at s.t.p.
Which mixture of gases has the greatest density?
planet major gases / % by number of molecules
A Jupiter H2 89.8, He 10.2
B Neptune H2 80.0, He 19.0, CH4 1.0
C Saturn H2 96.3, He 3.25, CH4 0.45
D Uranus H2 82.5, He 15.2, CH4 2.3
The approximate percentage composition of the atmosphere on four different planets is given in
the table below.
The density of a gas may be defined as the mass of 1 dm3
of the gas measured at s.t.p.
Which mixture of gases has the greatest density?
planet major gases / % by number of molecules
A Jupiter H2 89.8, He 10.2
B Neptune H2 80.0, He 19.0, CH4 1.0
C Saturn H2 96.3, He 3.25, CH4 0.45
D Uranus H2 82.5, He 15.2, CH4 2.3
This question has been previously explained- https://xtremepape.rs/threads/chemistry-post-your-doubts-here.9859/post-998865
hope it helps
The question has been previously explained- https://xtremepape.rs/threads/chemistry-post-your-doubts-here.9859/post-827046
all the best
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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?
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A few past paper questions but first
I need to know what's the method to find out bonds between elements in a molecule or elements
Also how do we solve questions in which we are giving some properties of elements like boiling point and conductivity and we have to find the elements cuz we don't know the boiling point of the elements so how? AN EXAMPLE OF THIS TYPE OF QUESTIONS
Now the past paper questions start please answer them all with explanations
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I need to know what's the method to find out bonds between elements in a molecule or elements
Also how do we solve questions in which we are giving some properties of elements like boiling point and conductivity and we have to find the elements cuz we don't know the boiling point of the elements so how? AN EXAMPLE OF THIS TYPE OF QUESTIONS
Now the past paper questions start please answer them all with explanations
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Hey are you also writing chem tomorrow?