StudentQns' chemistry questions
-
My teacher said that the more reactive turf a metal it, the more difficult it is to decompose its oxide. but K2O and Na2O has low melting points. so I'm not sure what that statement means... thanks for the help!
-
Originally posted by StudentQns:
My teacher said that the more reactive turf a metal it, the more difficult it is to decompose its oxide. but K2O and Na2O has low melting points. so I’m not sure what that statement means… thanks for the help!
I think your teacher mean metal carbonates. The more reactive the metal, the metal carbonate will be more thermal stable.
-
Also oxides right?
-
Then what about sulfates and nitrates?
-
Melting of ionic compounds is breaking the bonds between the ions. But then what is decomposition? Like they break the bonds then a new compound is rebonded? Thanks so much for the help!
-
Hi this came out in a spa practice for chem. I'm not sure why this happens: aqueous potassium iodide is placed into equal volume of nitric acid. Divide the solution into 2 portions and carry out the following test. Add aqueous lead (II) nitrate. Heat the solution and cool under the tap. My observation: a yellow ppt it formed. When heated more of the yellow ppt is formed. When cooled it crystallises at the sides of the test tube. I think more forms cos there are more active collisions by the lead ions and iodide ions so more will be formed..but the crystallising of the lead iodide I'm not sure. Thanks for the help!
-
Originally posted by StudentQns:
Then what about sulfates and nitrates?
The boiling point of Na2O isn't low, it has a melting point of 1132 degrees celcius. You can apply that to oxides, sulfates, nitrates as well. Usually O level will only ask you about the thermal decomposition of metal carbonates. And you can use the general metal reactivity series to answer your questions.
However, just for your information, to explain individually why a particular metal carbonate is more reactive than another metal carbonate, you need to compare within a group (for example down a group) or the element of the same period (eg. Na and Mg). And this is not required at O level.
"Melting of ionic compounds is breaking the bonds between the ions. But then what is decomposition? Like they break the bonds then a new compound is rebonded?"
Yes, you are right. Thermal Decomposition is the a chemical reaction that uses heat to break up a compound to form new compound.
"Hi this came out in a spa practice for chem. I’m not sure why this happens: aqueous potassium iodide is placed into equal volume of nitric acid. Divide the solution into 2 portions and carry out the following test. Add aqueous lead (II) nitrate. Heat the solution and cool under the tap.
My observation: a yellow ppt it formed. When heated more of the yellow ppt is formed. When cooled it crystallises at the sides of the test tube.
I think more forms cos there are more active collisions by the lead ions and iodide ions so more will be formed..but the crystallising of the lead iodide I’m not sure."
The yellow ppt is Lead (II) Iodide. It is not soluble in cold water. But it is quite soluble when dissolve in hot water. Thus, when the hot solution of lead (II) iodide is cooled down, lead (II) iodide will crytallise out as yellow ppt.
-
Originally posted by EiN930:
The boiling point of Na2O isn't low, it has a melting point of 1132 degrees celcius. You can apply that to oxides, sulfates, nitrates as well. Usually O level will only ask you about the thermal decomposition of metal carbonates. And you can use the general metal reactivity series to answer your questions.
However, just for your information, to explain individually why a particular metal carbonate is more reactive than another metal carbonate, you need to compare within a group (for example down a group) or the element of the same period (eg. Na and Mg). And this is not required at O level.
"Melting of ionic compounds is breaking the bonds between the ions. But then what is decomposition? Like they break the bonds then a new compound is rebonded?"
Yes, you are right. Thermal Decomposition is the a chemical reaction that uses heat to break up a compound to form new compound.
"Hi this came out in a spa practice for chem. I’m not sure why this happens: aqueous potassium iodide is placed into equal volume of nitric acid. Divide the solution into 2 portions and carry out the following test. Add aqueous lead (II) nitrate. Heat the solution and cool under the tap.
My observation: a yellow ppt it formed. When heated more of the yellow ppt is formed. When cooled it crystallises at the sides of the test tube.
I think more forms cos there are more active collisions by the lead ions and iodide ions so more will be formed..but the crystallising of the lead iodide I’m not sure."
The yellow ppt is Lead (II) Iodide. It is not soluble in cold water. But it is quite soluble when dissolve in hot water. Thus, when the hot solution of lead (II) iodide is cooled down, lead (II) iodide will crytallise out as yellow ppt.
But compared to MgO, it has a lower melting point but MgO Is easier to decompose than Na2O. so I'm unclear on this thing. also when does a compound decompose and when does it melt? Like since MgO is easier to decompose shouldn't it have a higher melting point? Thanks for the help! -
Since decomposition also involves the breaking of ionic bonds then if MgO is easier to decompose then it should have a lower melting point than something that is harder to decompose such as Na2O.. I'm quite confused about this concept here. Thanks for all the help!
-
Originally posted by StudentQns:
But compared to MgO, it has a lower melting point but MgO Is easier to decompose than Na2O. so I'm unclear on this thing. also when does a compound decompose and when does it melt? Like since MgO is easier to decompose shouldn't it have a higher melting point? Thanks for the help!It is quite hard to compare between melting point and the temperature at which decompose.
Melting is a physical change (solid to liquid) and thermal decomposition is a chemical process.
Consider the case of Sodium Carbonate and Magnesium Carbonate. Magnesium is expected to have a higher melting point than sodium carbonate, due to Magnesium having a higher charge.
However, due to the fact of this higher charge, the Mg2+ ions is able to polarize the carbonate ion and cause the CO2 to leave, leading to thermal decomposition. So the question is, which process will take place then?
Well this qn is hard to answer. So the way to look at it is to carry out the experiment and see really happens. Based on experimental data, it will seem if you apply heat to solid magnesium carbonate, it will decompose rather than melt. In fact, I can't find the temperature at which solid magnesium carbonate melts. I can only find the temperature at which it decompose, so from here, you can see it will decompose rather than melt.
As for sodium carbonate, only the melting point can be found. So there you go, sodium carbonate will melt than decompose.
From here, you can see that it is quite ambigious. It all really depends on what will happen if you carry out in the real experiment. Anything written on paper is not proven until tested.
And because of the ambiguity, such questions were not be tested in O levels.
Lastly, I admire your desire to ask more questions to better understand things. And i also gained some knowledge as well. I welcome you to ask more questions. However, there's a limit of how many questions you should ask. Because I personally feel that sometimes knowing too much might end up confusing you even more and some questions just cannot be answer due to its ambiguity.
-
Oh ok thanks! I got confused about this cos melting involves the breaking of bond and so does decomposition. So I went on to associate them together as similar processes. Yup! I'm really curious about stuff and dig deep into higher level stuff. But I think I should stop at here: melting is different from decomposition so I won't associate them together. Metals that are more reactive will have more thermally stable compounds which equates to it being harder to decompose. I think its a general statement that more reactive metal compounds form stronger ionic bonds than less reactive metals. This is somewhat associating the decomposition of carbonate/etc to melting. So its somewhat correct yet general statement only. I didn't really agree to this at first cos Na2O's melting point was lower than MgO. My school teacher was the one who told us about this. If he said more thermally stable, I would agree with him now :) Thanks so much for the help EiN930! Really appreciate your help in this!
-
Originally posted by StudentQns:
Oh ok thanks! I got confused about this cos melting involves the breaking of bond and so does decomposition. So I went on to associate them together as similar processes.
Yup! I’m really curious about stuff and dig deep into higher level stuff. But I think I should stop at here: melting is different from decomposition so I won’t associate them together. Metals that are more reactive will have more thermally stable compounds which equates to it being harder to decompose.
I think its a general statement that more reactive metal compounds form stronger ionic bonds than less reactive metals. This is somewhat associating the decomposition of carbonate/etc to melting. So its somewhat correct yet general statement only. I didn’t really agree to this at first cos Na2O’s melting point was lower than MgO. My school teacher was the one who told us about this. If he said more thermally stable, I would agree with him now
Thanks so much for the help EiN930! Really appreciate your help in this!
No problem. I always welcome you to ask qn to clarify your doubts.
-
Hi EiN930, is there any O level explanation on why reactivity decreases across the period? Thanks for the help! :)
-
Originally posted by StudentQns:
Hi EiN930, is there any O level explanation on why reactivity decreases across the period?
Thanks for the help!
You cannot make an assumption that reactivity decreases across the period. Do not forget that the elements becomes less metallic across a period. So you should compare the reactivity of metals and non-metals separately.
For example, across the period, metals becomes less reactive; non-metals become more reactive.
However, O level will only require you to explain the reactivity down a group (Group I & VII).
-
OOriginally posted by EiN930:
You cannot make an assumption that reactivity decreases across the period. Do not forget that the elements becomes less metallic across a period. So you should compare the reactivity of metals and non-metals separately.
For example, across the period, metals becomes less reactive; non-metals become more reactive.
However, O level will only require you to explain the reactivity down a group (Group I & VII).
oh ok i understand. i have a metal displacement question to ask you i know that when a more reactive metal is placed into a salt solution with the cation being less reactive. displacement will occur. this is because the metal atom will transfer its electrons into the postive cations. so the less reactive cation will form into a solid metal because it is subjected to metallic bonding since it now has the valence electrons while the more reactive metal will form an ion which forms a soluble ionic salt which dissolves in water. However, when a metal displaces a metal oxide (both are solid) a lot of heat is required for the reaction to occur. so in this case, how does the reaction occur? what enables the metal to pass its electron to the less reactive metal ions? thanks so much for the help! You guys rock! -
If the heat provides the two substances with enough of energy, the oxide does not have to melt right? They can both remain as solids and heat provided for the reaction?
-
Originally posted by StudentQns:
oh ok i understand. i have a metal displacement question to ask you i know that when a more reactive metal is placed into a salt solution with the cation being less reactive. displacement will occur. this is because the metal atom will transfer its electrons into the postive cations. so the less reactive cation will form into a solid metal because it is subjected to metallic bonding since it now has the valence electrons while the more reactive metal will form an ion which forms a soluble ionic salt which dissolves in water. However, when a metal displaces a metal oxide (both are solid) a lot of heat is required for the reaction to occur. so in this case, how does the reaction occur? what enables the metal to pass its electron to the less reactive metal ions? thanks so much for the help! You guys rock!You have already answer in your own question. For the reaction to occur, you would need energy. That's why heating is carried to suppy as a form of energy.
The reaction of metal displacing a metal oxide is also a displacement reaction. It is called a thermite reaction.
For the reaction to occur, you need to heat to a certain temperature,and that temperature is probably below the melting point of the oxide.
-
Oh ok thanks :)
-
Hi, I know that a more reactive metal will oxidize rather than the less reactive metal when they are in contact or a wire is connected to each other. So when iron gets slightly oxidized, the electrons will reduce it. So how does the more reactive metal like zinc when galvanizing an iron bin or when its underground gets its anions for it to oxidize (Zn2+ and O2- for example) ? Underground there might be some anions for the reaction, but for the bin case how does it get the anions since air doesn't have any anions. I read on galvanizing corrosion they say that as long as moisture is present the zinc will corrode instead of Fe, I don't quite understand this. is it possible that the air has H2O so it transfer the oxygen ions it displaces from the iron when it starts to rust a little. so the equation would look like this Zn+Fe2O3>ZnO+Fe? Also, if i attach a block of magnesium to a huge rusted metal it would not reverse the rusting to give me a nice block of iron right? So must the Fe2O3 that i mentioned above be really minute so that the activation energy is very very little such that the electrons are already enough to reduce the Fe2O3? thanks for the help! (my teacher told us about the electron giving thing, but in the textbook it just said that the more reactive metal will corrode in place of the less reactive metal thus iron will not rust until the more reactive metal has completely corroded away. So this might be too high level for me?) Really appreciate you guy's help!
-
hi ive got a chem question to ask. in O levels do i consider aqueous ammonia to be NH3 or NH4OH? like when i write chemical equations im not sure which to put cos: NH4OH+HCl--> NH4Cl+H2O or NH3+HCl--> NH4Cl thanks for the help!
-
Hi guys, I was wondering if O level chem requires us to name the organic compounds that are branched like the isomers. Or to draw it out. Thanks for the help guys! :-)
-
Originally posted by StudentQns:
Hi guys, I was wondering if O level chem requires us to name the organic compounds that are branched like the isomers. Or to draw it out. Thanks for the help guys! :-)
Yes, name for simple ones + structure for simple ones
Do expect 3 hydroxy nonanoic acid
-
Originally posted by StudentQns:
hi ive got a chem question to ask. in O levels do i consider aqueous ammonia to be NH3 or NH4OH? like when i write chemical equations im not sure which to put cos:
NH4OH+HCl-
> NH4Cl+H2O-> NH4Cl
or
NH3+HClthanks for the help!
either NH4+OH- or NH3 is fine, use NH3 is better
-
I can roughly name some stuff this are the following rules that I apply when naming: 1) alphabetical order despite the number in front 2) for alkanes make sure number is the smallest when added together 3) for alkenes and alcohols number the carbon atoms by seeing which side is the shortest for the functional group then the other alkyl group will follow that numbering But for the example you gave, I had not heard of alcohols that are name like that though. So far I had only named stuff like propan-2-ol and maybe the alkyl or halogen attached to it.
-
Because in the textbook we aren't given any information about naming isomers so I'm a bit confused about this too. I was also wondering about how to name organic compounds with 2 or more functional group like the example you gave where a hydroxy group and the COOH group. Thanks for the help!