Important Chemistry Questions! Answer Them As Soon As You See Them! (1 Viewer)

[digimonstudent]

i dont get how to write balanced equations. i mean ionic ones r easy n covalent ones ain't that hard but i cant understand how to write balanced equations espicially if most of them involve using matalloids n transition metals. how do we even determine their valence?

1)write the balanced equation of this:

lead sulfide + oxygen -----> lead oxide + sulfur dioxide

2)what does this formulae mean CU(OH)_2.CuCO_3. why is a bracket used?

3)in electron configuration some atoms which have about 20 electrons. why are only a maximum of 8 electrons placed in the third shell if its maximum capacity is 18?

 

[Pwnage101]

1) for metals with more than one valence state, we put brackets in the worded formula, ie when they say 'lead sulfide' this is incorrect notation, since there can be Lead (II) Sulfide [PbS] and Lead (IV) Sulfide [PbS2] [wikipedia is a great resource for these], but i would say they are referring to the more common PbS [Lead (II) Sulfide] so i rekon the reaction would be:

2PbS_(s) + 3O_2(g) ---> 2PbO_(s) + 2SO_2(g)

2) bracket is used bcause it has 2 molecules of Hydroxide (OH) - if no brackt was used it would not be Copper (II) Hydroxide, as the subscript 2 would only signify 2 atoms of hydrogen (and not 2 molecules of hydroxide)

3). Hmmm...prelim so long ago...octet rule states 8 is stable configuration

PS this should be in the chemistry forum

 

[digimonstudent]

1) for metals with more than one valence state, we put brackets in the worded formula, ie when they say 'lead sulfide' this is incorrect notation, since there can be Lead (II) Sulfide [PbS] and Lead (IV) Sulfide [PbS2] [wikipedia is a great resource for these], but i would say they are referring to the more common PbS [Lead (II) Sulfide] so i rekon the reaction would be:

2PbS_(s) + 3O_2(g) ---> 2PbO_(s) + 2SO_2(g)

2) bracket is used bcause it has 2 molecules of Hydroxide (OH) - if no brackt was used it would not be Copper (II) Hydroxide, as the subscript 2 would only signify 2 atoms of hydrogen (and not 2 molecules of hydroxide)

3). Hmmm...prelim so long ago...octet rule states 8 is stable configuration

thanks for the answers but would u mind explaining to me how to write balanced equations?

 

[yummy-cookies]

Well, most of the transition metals have a valence of 2. But for most of them, their actual valence is given to you (in the question).

1) Not sure, but I think:

2PbS + 3O2 * 2PbO + 2SO2 ​

Pb has a valency of +2, S is -2, O is -2
So lead sufide must be PbS, etc
Balance the equation by making sure there are equal numbers of each element on both sides

2) Copper hydroxide. copper carbonate. The bracket is used to show that there are lots of the hydroxide group (OH) to every copper atom. Without the bracket it would read as CuOH2 and represent an molecule with 1 copper, 1 oxygen, and 2 hydrogens (as opposed to 1 copper, 2 oxygens, and 2 hydrogens)

3) The maximum capacity of the third shell is 18. However, after the third shell fills up with 8 electrons, following electrons will go into a subshell - the fourth shell.

 

[0hNivlek]

The reason why i didn't choose Chemistry lol!

 

[Pwnage101]

thanks for the answers but would u mind explaining to me how to write balanced equations?

i honestly think you should wait until you're taught this in class next year

 

[digimonstudent]

Well, most of the transition metals have a valence of 2. But for most of them, their actual valence is given to you (in the question).

1) Not sure, but I think:

2PbS + 3O2 �* 2PbO + 2SO2 ​

Pb has a valency of +2, S is -2, O is -2
So lead sufide must be PbS, etc
Balance the equation by making sure there are equal numbers of each element on both sides

2) Copper hydroxide. copper carbonate. The bracket is used to show that there are lots of the hydroxide group (OH) to every copper atom. Without the bracket it would read as CuOH2 and represent an molecule with 1 copper, 1 oxygen, and 2 hydrogens (as opposed to 1 copper, 2 oxygens, and 2 hydrogens)

3) The maximum capacity of the third shell is 18. However, after the third shell fills up with 8 electrons, following electrons will go into a subshell - the fourth shell.

but y did u put 2 before the Pb n 3 before the O. why not the other way around?

 

[digimonstudent]

i honestly think you should wait until you're taught this in class next year

NO! I NEED TO KNOW NOW!

ur a tutor anyway. cant u answer a simple question?

 

[yummy-cookies]

but y did u put 2 before the Pb n 3 before the O. why not the other way around?

2PbS + 3O2 ----> 2PbO + 2SO2

Step by step:

1. Lead sulfide + oxygen ----> Lead oxide + sulfur dioxide

2. You should know what each of the formulae are, so you know that the unbalanced equation is:

PbS + O2 ----> PbO + SO2

3. This is unbalanced because there isn't an equal number of each element on either side
Eg. There are 2 O atoms on LHS, and 3 on the other

4. To balance the equation, play with numbers. Since we need to have and even number of O on RHS (as we can only have an even number on the RHS due to the O2), try multipling PbO by two. We now have 4 O on RHS, so we form 2 pairs of O2 on LHS

PbS + 2O2 ----> 2PbO + SO2
Now we have a uneven number of Pb. Multiply PbS by 2.

2PbS + 2O2 ----> 2PbO +SO2
Uneven number of S: multiply that by 2 to even it out. We now have 6 O on RHS, meaning we need 3 pairs of O2 on the LHS. Hence we end up with

2PbS + 3O2 ----> 2PbO + 2SO2
It's now balanced - there are an equal number of each element on each side
​

 

[dp624]

You need to make sure that there are the same number of Os on each side, the same number of Pbs etc

 

[Pwnage101]

NO! I NEED TO KNOW NOW!

ur a tutor anyway. cant u answer a simple question?

calm down mate

learn a lesson in life: if someone is helping you out (and they don't have to be doing it), treat them with respect, or else you'll find they wont be so kind as offer you help

as a tutor, i would advise you learn yr 11 chemistry in class because it gives you a grounding in chemistry - you havent done this much chemistry yet

sure, if you are an 09er and wnat to get ahead of things in these holidays i would say go for it, since yr 12 is building upon yr 11 in many ways, and the content is not hard to understand with the yr 11 knowledge of the chemistry basics

you dont have these basics, and the best way to learn these will be in class, in my opinion

good day to you sir

 

[imoO]

calm down mate

learn a lesson in life: if someone is helping you out (and they don't have to be doing it), treat them with respect, or else you'll find they wont be so kind as offer you help

as a tutor, i would advise you learn yr 11 chemistry in class because it gives you a grounding in chemistry - you havent done this much chemistry yet

sure, if you are an 09er and wnat to get ahead of things in these holidays i would say go for it, since yr 12 is building upon yr 11 in many ways, and the content is not hard to understand with the yr 11 knowledge of the chemistry basics

you dont have these basics, and the best way to learn these will be in class, in my opinion

good day to you sir

This man is right. Listen to him. Its a 99.9 UAI calibre student for god's sake. But because you're so persistent, its to balance out the number of atoms of each element on both sides.

 

[Pwnage101]

fine, since i'm in a good mood i'll help u out:

there is no 'secret' to balancing equations, there is no '5 steps to balance an equation' (or if there is, ive never heard of it)

basically why there needs to be the same amunt of atoms on each side of the equation is ( as you will learn in year 11) because of the law of conservation of matter/mass:

"the mass of a closed system will remain constant, regardless of the processes acting inside the system. An equivalent statement is that matter cannot be created/destroyed, although it may be rearranged" - Wikipedia

(the 2nd part of that is a better way of putting it )

Wikipedia continues by saying "This implies that for any chemical process in a closed system, the mass of the reactants must equal the mass of the products."

so there needs to be the same amount of atoms of each element on the products side as there is on the reactants side, although they have been reaarranged, and this is how balancing occurs

balancing comes with practice, and can involve trial and error in some instances

check out the link for further help:

http://letmegooglethatforyou.com/?q=balancing+chemical+equations

 

[zzzz12345]

i dont get how to write balanced equations. i mean ionic ones r easy n covalent ones ain't that hard but i cant understand how to write balanced equations espicially if most of them involve using matalloids n transition metals. how do we even determine their valence?

1)write the balanced equation of this:

lead sulfide + oxygen -----> lead oxide + sulfur dioxide

2)what does this formulae mean CU(OH)_2.CuCO_3. why is a bracket used?

3)in electron configuration some atoms which have about 20 electrons. why are only a maximum of 8 electrons placed in the third shell if its maximum capacity is 18?

Balancing chemical equations ties in with the Law of conservation of matter i.e. Matter cannot be created or destroyed. This means that what you have on the left hand side of the arrow MUST be present on the right hand in accordance with this law. When balancing chemical equations first you would write out the chemical formulas of the reactants and then the products and then count the specific atoms to ensure that there is an equal number on each side. If look at the example of the electroysis of water. The word equation would be: Water ---> Hydrogen Gas + Oxygen Gas.
The equation in chemical symbols would be H2O(l)-->H2(g)+O2(g) however if you look at the equation you have 1 oxygen on the left hand side and two on the right handside which doesn't accord with the law of conservation of matter. To correct this we would put a '2' infront of the H2O but as now we would have 4 hydrogens on the left-hand side we would also have to put a 2 in front of the H2 on the right hand side. Thus our completed equation would be: 2H2O(l)--->2H2(g)+O2(g) and the equation is now balanced.
For your other question regarding placement of electrons in shells; the real answer is the subshells of each shell (Note that this is NO longer in the syllabus and you do NOT need to know this). Each shell has a corresponding number of subshells e.g. The first shell has one; the second has two etc. These subshells are named s, p, d, f (I think) and can hold 2, 6, 10 and 14 electrons respectively. It is easier to fill e.g. The 4s subshell rather than the 3d shell and thus shells would be filled following this pattern: 1s2s2p3s3p4s3d4p5s4d...and etc. It is from this that 8 (The s and p total) in a new shell forms before the 18 that can be held by the third shell. I make the point now that you do NOT need to know this but this is a little background information. Essentially in terms of our Chem syllabus you have to know that a full shell or 8 in the outer shell makes the atom stable and it desires to achieve this configuration (i.e. the octet rule).
I'm surprised that you haven't encountered balancing equations before but if you want to get better at it I suggest practice as the more you get used to them the easier it gets but don't try to get too far ahead of your class. The instructions of your teacher are very helpful in gaining understanding of new concepts.

 

[Pwnage101]

Balancing chemical equations ties in with the Law of conservation of matter i.e. Matter cannot be created or destroyed. This means that what you have on the left hand side of the arrow MUST be present on the right hand in accordance with this law. When balancing chemical equations first you would write out the chemical formulas of the reactants and then the products and then count the specific atoms to ensure that there is an equal number on each side. If look at the example of the electroysis of water. The word equation would be: Water ---> Hydrogen Gas + Oxygen Gas.
The equation in chemical symbols would be H2O(l)-->H2(g)+O2(g) however if you look at the equation you have 1 oxygen on the left hand side and two on the right handside which doesn't accord with the law of conservation of matter. To correct this we would put a '2' infront of the H2O but as now we would have 4 hydrogens on the left-hand side we would also have to put a 2 in front of the H2 on the right hand side. Thus our completed equation would be: 2H2O(l)--->2H2(g)+O2(g) and the equation is now balanced.
For your other question regarding placement of electrons in shells; the real answer is the subshells of each shell (Note that this is NO longer in the syllabus and you do NOT need to know this). Each shell has a corresponding number of subshells e.g. The first shell has one; the second has two etc. These subshells are named s, p, d, f (I think) and can hold 2, 6, 10 and 14 electrons respectively. It is easier to fill e.g. The 4s subshell rather than the 3d shell and thus shells would be filled following this pattern: 1s2s2p3s3p4s3d4p5s4d...and etc. It is from this that 8 (The s and p total) in a new shell forms before the 18 that can be held by the third shell. I make the point now that you do NOT need to know this but this is a little background information. Essentially in terms of our Chem syllabus you have to know that a full shell or 8 in the outer shell makes the atom stable and it desires to achieve this configuration (i.e. the octet rule).
I'm surprised that you haven't encountered balancing equations before but if you want to get better at it I suggest practice as the more you get used to them the easier it gets but don't try to get too far ahead of your class. The instructions of your teacher are very helpful in gaining understanding of new concepts.

good explanation, although i think the subshells info is a bit advanced for someone who isnt in year 11 yet

 

[zzzz12345]

good explanation, although i think the subshells info is a bit advanced for someone who isnt in year 11 yet

I know, but I've always believed that it's better that you know the real explanation instead of swallowing down something simplified as you're not expected to understand something of that complexity. Plus it stops people questioning your explanation if you give them the full outline. It's his choice if he decides to take it on board or not (and I did mention that it's not in the syllabus and that he doesn't need to know it) and besides; an explanation from a student/someone who he can relate to more would probably be better than stumbling across references to subshells on the internet which would generally be much more advanced than the outline I posted.

 

[Omium]

I know, but I've always believed that it's better that you know the real explanation instead of swallowing down something simplified as you're not expected to understand something of that complexity. Plus it stops people questioning your explanation if you give them the full outline. It's his choice if he decides to take it on board or not (and I did mention that it's not in the syllabus and that he doesn't need to know it) and besides; an explanation from a student/someone who he can relate to more would probably be better than stumbling across references to subshells on the internet which would generally be much more advanced than the outline I posted.

Trust me when i say this, Chemical Bonding is MUCH more complex that what year 11/12 teach. It will be very hard to explain everything.

 

[zzzz12345]

Trust me when i say this, Chemical Bonding is MUCH more complex that what year 11/12 teach. It will be very hard to explain everything.

I'm aware of that and I know there are facets of Chem that are much too complex for a Year 11/12 student but where possible, I believe that the actual explanation is better than a watered down version. I know that there are exceptions with this as there are with most generalisations and that they exist in the chemical realm but I still prefer knowing the actual explanation and try to offer it to others. It is up to the OP whether he finds it useful or not.

 

[digimonstudent]

calm down mate

learn a lesson in life: if someone is helping you out (and they don't have to be doing it), treat them with respect, or else you'll find they wont be so kind as offer you help

as a tutor, i would advise you learn yr 11 chemistry in class because it gives you a grounding in chemistry - you havent done this much chemistry yet

sure, if you are an 09er and wnat to get ahead of things in these holidays i would say go for it, since yr 12 is building upon yr 11 in many ways, and the content is not hard to understand with the yr 11 knowledge of the chemistry basics

you dont have these basics, and the best way to learn these will be in class, in my opinion

good day to you sir

sry man i was just in a rotten mood earlier cause i was staring at my textbook for ages n couldnt figure it out.

 

[Pwnage101]

I'm aware of that and I know there are facets of Chem that are much too complex for a Year 11/12 student but where possible, I believe that the actual explanation is better than a watered down version. I know that there are exceptions with this as there are with most generalisations and that they exist in the chemical realm but I still prefer knowing the actual explanation and try to offer it to others. It is up to the OP whether he finds it useful or not.

while i like how u go beyond the syllabus, sometimes its best just to stick within it, esp when explaining stuff

lol remember what they were teaching us in year 7, that light is a wave and electrons are partciles that orbit the nucleus?


then in yr 12 physics u learn that it all changes, but then how else do they teach you the basics?

there's a time for everything, but yeh it is good (and ive done this personally) to look beyond the syllabus if interested