Wednesday, September 22, 2010
Help questions while on paternity leave
Nick is getting into a regular schedule now at the ripe old age of six days, so I should be able to find time every day to respond to some questions regarding class material. I will try and respond daily, so check back every day if you post a question. Mr. Aversa is doing a wonderful job helping you out, and has been giving me good reviews about your progress thus far. Remember to work diligently in class every day, keep up with your records and homework, and follow the strategies for success whenever you are working. To ask a question, post a comment by clicking on "comments" below, leave your first name or initial (NO LAST NAMES) and class (chemistry 1 or chemistry AP), and then leave a clear question that could be answered by me in a couple of sentences. Make sure to identify yourself somehow, so I can address your question directly. I have posted an example of a question and a response below.
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50 comments:
This is S from Chemistry 1. I am wondering how you would know the formula for salt (NaCl (s)) added to water (H2O). How would you know what resulted?
Well S (funny because I was already logged in), when salt is added to water, it is no longer solid salt (s), it is in it's aqueous state (aq). No chemical reaction has occurred, as shown in lesson 6 A New Language. Recall the multiple salts (NaOH, CuSO4, NaCl) were also in vials in the aqueous state, after they had been added to water.
This is J from AP Chem. I have several questions from the worksheets:
1)Why are K2CO3 [9-3] and CoCl2 [9-1] solids? I thought K2CO3 was soluble because K is in Group and that CoCl2 was soluble because Co is not an exception.
2)Why is there no reaction for 9-1 #6?
3) How does one know that a reaction can be reversed?
4) Why won't K2ClO3 and KCl ionize? [10-1 #3]
5)[this is from the textbook]What does the reaction of CH3NH2 and HCHO2 look like?
Thanks!
This is H from AP Chemistry. I was wondering why there isn't a box for the students' name in survey 3.
This is A from AP Chemistry. I was also wondering why there isn't a box for the students' name in survey 3.
Would it be okay if I wrote my name in one of the answer boxes?
H & A: a name box has been added. If you have already completed your survey, send me an email that tells me roughly what time you took it, and I will be able to figure out who took each survey.
For J's questions, in order:
1. K2CO3 is a solid, because it is produced out of solution (no water). CoCl2 is right on the line of soluble/not soluble. Different charts may even say different things. NR is the only other option.
2. There is no precipitate, gas, or molecular substance formed that is a net ionic reaction.
3. All reactions can be reversed to some degree. Right now if there is no net reaction, product--> reactant and reactant--> product can be considered to happen in equal amounts. When we study equilibrium later this year, we will learn much more about this topic.
4. In both cases, these substances are solid salts, not in solution, and are thereby written as solids, not ions.
5. This would be a weak-acid/weak-base reaction. The weak acid (HCHO2) would donate an H+ to the base. This is also referred to a Bronsted-Lowry acid-base reaction.
Right, this is R from Chemistry AP and these are kind of odd questions, so sorry if they may not make much sense:
1. When writing ionic equations and breaking down the ions, if the two reactants both donate the same ion (ex. H+), do you still write both ions in the reactants separately?
2. Following up on J's question, how would we be able to distinguish if a molecule is "on the line" of soluble/not soluble? Is there a specific atomic weight? If not, which atoms should we keep in mind?
this is L from AP chemistry
1) does a net ionic equation not exist if there are all aq products and reactants?
2) Why do you write HOH instead of H2O for some of the answers to questions?
3) this is just a minor thing but the worksheets told us to balance the equation but you gave us the answers in net ionic? should we just assume when it says write the equation out it means net ionic?
R, if both reactants donate an H+, it is unlikely that there would be a net ionic reaction, because there would no new product produced. However, if there were some case where both reactants donated the same species and others, and there was a net ionic reaction, then a coefficient in front could take care of that. You wouldn't write the same ion twice. Solubility is determined by many properties. Ultimately, a stronger attraction between the ions than between the ions and water is the cause. We will learn about other strategies, but right now just learn the rules from the document on the website/the book and you will be right 9/10 times.
L, there is no net ionic equation if everything is in solution. It would just be a bunch of ions bouncing around.
It is useful to write water as HOH because it is often formed from H+ and OH- as a metathesis product, so it just helps you remember. Either way is fine, HOH just helps me remember that it can form from two products like that.
That was more a function of me rushing than anything else. The overall sequence is to balance the molecular equation, separate it into a full ionic, then eliminate spectator ions to be left with the balanced net ionic equation.
This is C from AP chem. Why is number 3 on 9-1 no reaction? Aren't compounds with alkali metal supposed to be soluble?
Also, how can you tell whether there is a precipitate? Are there rules like the solubility rules?
C, compounds with alkali metals are soluble. However, chromate is soluble with sodium AND lithium, and likewise with hydroxide. Therefore, there is no net reaction, only ions as reactants & products.
Precipitation is predicted with the solubility rules. If one of the produces is insoluble, where all the reactants were soluble, that insoluble product is a precipitate.
This is A from AP chemistry. Could you explain number 9 from 9.3?
A, oxalic acid, H2C2O4 is diprotic, meaning it donates 2 protons to solution as an acid assuming it ionizes completely:
H2C2O4 --> 2H + + C2O4 2-
cesium hydroxide on the other hand, only has one OH-, so with equal concentrations of 0.1 M, there would only be enough OH- to react with 0.1 M, thus leaving the CsHC2O4 product (or Cs+ + HC2O4- in ionic form). When acids have more than one "acidic proton" you have to pay attention to the concentration of the reactants too!
Hi, this is C from AP Chemistry.
I was wondering why there is no box for our names on survey 4?
this David vyshedsky at 5:31 i just posted my survey and didnt write my name.9/28
There is no name slot on survey 4. Should we just write our names in the answer slots?
This is A from AP Chemistry and I noticed that there was no section for the names on Survey 4, so I wrote my name in the last answer box. Is that okay?
Hi Mr. Balicki, this is Jan from Chem 1. In lesson 14 we had to write the symbol for nickle, and its avg atomic mass is 58.69, do we round up that number when we write the isotope symbol ot does it stay as 58? Thank you!
For all of you who have commented on the lack of the name box for survey 4, thank you. I have added one at 8:25, so half of you will have no issue. If you have not already put your name in a box, as some have indicated, please shoot me an email with the approximate time you took the survey. That will help me figure out the few missing names.
Jan:
For the isotope symbol for Nickel, Ni-58 is in fact the most common isotope. It would also be reasonable to assume that there is a Ni-59, or even a Ni-60. The table in lesson 14 is meant to get you thinking about which isotopes would produce an average atomic mass of 58.69. Some would be higher than 58, others would be lower.
This is K from Ap Chem.
For Survey 4 you are asking for the balanced net ionic reaction. Would it be, for example:
Molecular: AgNO3(aq) + KCl(aq) --> AgCl(s) + KNO3(aq)
Ionic: Ag+(aq) + NO3-(aq) + K+(aq) + Cl-(aq) -->AgCl(s) + K+(aq) + NO3-(aq)
Net: Ag+(aq) + Cl-(aq) -->AgCl(s)
or just
Ag+(aq) + Cl-(aq) -->AgCl(s)?
Thanks!
K:
The last one is a balanced net ionic equation.
This is C from Chemistry 1. While we were reviewing isotopes in the workbook in class today, one question asked how many isotopes certain elements have. I understood how to find the number of isotopes in elements with only 1 or 2 isotopes, but is there a way to figure out if an element has 3 or more isotopes (for example H or Ar)?
C:
There is not a way to determine that exactly. Right now you should just be able to predict what the two isotopes would be, assuming there were two. When you work a little further you will learn about the "band of stability", and why certain neutron:proton ratios occur in natural elements and others don't. However, even this cannot provide information to be able to exactly predict all isotopes. For a definitive answers, scientists need to check empirical data (or see which isotopes are ACTUALLY out there).
This is J from chemistry one. One the survey on Thursday I was wondering if there are going to be specific questions on the reading or if we should just try and remember as much as we can. Thanks!
J:
The survey will focus on the things that you have been studying in class. If you understand the worksheets/class work, you should be good.
Hi Mr. Balicki. This is J from chemistry 1 and I was wondering what a d-block element is?
J:
Any element with its outermost electrons in the d-subshell is considered a "d-block" element. This means all the transition elements in the middle of the periodic table.
I read tonight's homework, and in the section about the formation of elements, it said that there is almost no elemental difference between humans and bacteria except that silicon is different by a factor of 6. I thought I had to refer to the chart on the website, but I still don't understand how silicon is different by a factor of 6 and exactly what that means.
Hey Mr.Balicki this is T from Chemistry 1. I was pretty unclear about the effects of alpha particles and beta particles. The whole lesson 16 was a bit blurry.
This is C from Chemistry 1, i'm confused on how you know how many neutrons are in an isotope and how to figure out how many isotopes are in an element, or is it only by using the graph?
No name:
A factor of six refers to the difference in how much of that element is present in humans vs. bacteria.
T:
A bit blurry doesn't really lend itself to any comments. You need to ask specific questions.
C:
Every isotope of a given element will have the same number of protons. Total mass-#protons=#neutrons. To find the number of isotopes of an element, you need to use the graph.
This is L from Chemistry I. I am confused on Beta Decay and do not understand it.
This is C from AP Chemistry. I have a few questions on the Metathesis Reactions worksheet:
1) Why is (NH4)2CO3 not ionized? I thought all NH4 are soluble [D]
2) Why are Sr(OH)2 and HgCl2 ionized? Going by the solubility rules I thought they wouldn't. [H and J]
3) Why does H2PO4 not have a charge of -1? [K]
L:
Beta decay is not an easy thing to understand. The short answer is that changes occur in the nucleus to produce the beta particle. Because protons and neutrons are not fundamental particles, the quarks that build them can undergo changes resulting in beta decay. When beta (in our case, beta minus) decay occurs, the neutron, composed of two down quarks and one up quark, has one down quark spontaneously "flip" to an up quark, with an electron being emitted to conserve mass-energy. This may seem weird, but it happens all the time, even to a very small extent to the atoms in our body. The key thing to be able to do is predict that elements that undergo beta (-) decay will keep their atomic mass, and go up one atomic number, thus changing identity.
C:
(NH4)2CO3 is not ionized because it is in the solid state. If it were (aq) it would be, but it is solid. Remember to check states of matter, that makes a difference for how you write the ionic/net ionic!
HgCl2 and SrOH2 would technically be considered suspensions, in which there are some ions, and some suspended solid. If you have ever seen milk of magnesia, this is an example of a suspension. We will do a lab later in the year that involves substances like this, which will help you understand the idea a little bit better.
H2PO4 should have a charge of - and not 2-. My typeo. Thanks for spotting it!
This is M from AP chemistry.
According to you ionic equations powerpoint, H2SO4 is the only polyprotic acid that can be ionized into H+ + HSO4-.
I'm a little confused because I thought that H2CO3 can also be ionized into H+ + HCO3-, despite its being a weak acid.
M:
H2SO4 is the only STRONG acid that is polyprotic. For our intents and purposes, H2SO4 --> H+ + HSO4- happens 100% of the time, whereas H2CO3 --> H+ + HCO3- happens infrequently because carbonic acid is a WEAK acid.
Are you going to post the answers for the solutions stoichiometry and also the work in the book?
No name:
We can go over that in class when I return Monday. As we return to a more traditional situation, I will not be posting the full solution to every assignment that we do in class online, but we can go over necessary ones during class.
This is N from AP chemistry. In your answer to letter B in the metathesis problems, why are there 8 hydrogens in the reactants and only six in the products?
N:
Interesting, somehow I never noticed that. This makes me thing that the product should be phosphorus acid (H3PO3) as opposed to phosphoric acid (H3PO4), which would have 3 waters on the reactant side to balance.
Hey Mr.Balicki, this is J from chemistry 1. what do you mean by two sources of error?
Sources of error are factors that contribute to things not being accurate in your experiment. For example, if a triple beam balance had a paper clip stuck to the pan, it would artificially read 1 gram high each time.
This is N from Chemistry 1, On the worksheet letter G, does the beginning size of the sample mean the parent isotope?
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