anthropos

(I am a 9th grade student. ) Acidified potassium dichromate (VI) is used to test for the presence of reducing agents. How do I derive the 6 electrons in the following ionic equation during which the test of a reducing agent like sulphur dioxide is carried out? Cr2 O7 2- (aq) + 14H+ (aq) +6e- ==> 2Cr3+ (aq) + 7H2O (l) How is dichromate (VI) ion reduced to chromium (III) ion? Cr2 O7 2- ---> 2Cr 3+ How can reduction result in a negative charge changed to a positive charge?

I was reading my Maths textbook for fun when I came across the chapter on combinations and permutations. The textbook states that the number of permutations of n different objects is n! = n(n-1) (n-2) x...x 3 x 2 x 1 Then how should we define 0! so that the above result would stilll hold?? I checked 0! = 1. Hmm... can somebody enlighten me how this works?

Thanks, yggdrasil. Now I have a better understanding of energy changes.

I have just learnt about endothermic and exothermic reactions. Um...since endothermic reactions absorb heat from the surroundings, why do the temperature of the solution drop after the reaction? Is evaporation endothermic or exothermic? Sorry, I really don't know...Itry to Google for it but I have people saying it is exothermic while the others say it's endothermic. SIGH

um...anyway...ignore the second question. I have asked my teacher about it and she said that there was something wrong with it...haha...

The following shows two stages in which the raw materials, zinc blende, ZnS, is converted to the metal zinc. 2ZnS (s) + 3O2 (g) --> 2ZnO (s) + 2SO2 (g) ZnO (s) +C (s) --> Zn (l) + CO (g) 194g of znc blend is used for this extraction process. The mass of zinc recovered from it is 125g. Write the overall reaction equation, with state symbols of this extraction process. --- 11.1 g of calcim chloride is added to 100cm3 of water. Calculate its concentration in a) g/dm3 and b) mol/dm3. The thing i want to ask is : Concentration (g/dm3) = Mass of solute (g) / Volume of solution in dm3 Therefore, do we use the volume of water only or use the volume of the CaCl2 + H20?

OMG O_O, thx Metafrizzics...and all the great guys in this thread

I mean at first I sent a message to Dave saying I don't understand, then later I seemed to grasp it (and not really at that same time...that ambiguity was horrible) and later with my teacher's aid, I totally grasp it!

Please read the attachments. Thanks, dudes. The teacher just started on this topic, and I am still very unfamiliar with the chapter.

oh...ok...thx...

AHA!!! I finally understand what's going on because we got back our papers and our dear teacher explained to us why! Aha, he was kind of frustrated because we only understood what was going on during his third attempt of explanation. Anyway, thanks Dave!

I think the first one is the best one, it has the most meaning. The second and third ones are empty of meaning and are just packed with special effects.

During fifth grade, our class had a heated discussion, and my friend said something really stupid. We laughed and the teacher said without thinking, "Oh, don't bullsh*t!" We all stared at her O_O. There was an uneasy silence.

Oh...great!!! Thx, primarygun!

oh...i see...thanks...^^

My textbook states that I can deduce the type of acid used to make a salt by analysing its negative ions. Calcium Chloride - CaCl2-----Ca-base ion Cl2-acid ion so you know that by CaO + HCL --> CaCl2 + H2O Then I saw the following: Ammonium sulphate - (NH4)2 S04-----(NH4)-base ion SO4-acid ion 2NH3 + H2O + H2SO4 --> (NH4)2 SO4 +H2O Um...is the 2NH3 dissolved in H2O to give NH3 (aq) [aqueous ammonia] and then added to H2SO4 for neutralisation? I mean, the 2NH3 + H2O is actually mere dissolving but not neutralisation, right? Sorry, guys, I don't know how to write subscripts on the forum....so it is rather hard to see what I am writing. Thanks, Anthropos

Oh...thanks...but I don't think I will do any more spoilers here...better be safe than sorry...

hmmm...okay...**batting my eyelids**

Teachers and parents never like their children say vulgarities because it will be very rude and uncivilised for them to do so, and some of them have sexual meanings. Is saying vulgarities totally, completely bad? (My phrasing sucks, but I think you know what I mean.)

Anyway, I also think that the Harry Potter series are getting more boring...the contents seem to be the same for every book!

I have made the necessary changes...(But I can't change the title...**sobs**...Thanks, Ollie! **Beaming** Bleh, anyway, I think Richard Harris is better at portraying Dumby than Michael Gambon... I read that Richard Harris at first refused but later wanted the role because his granddaughter (hmm...if I have remembered it correctly...i have a bad memory u_u") threatened not to speak to him anymore if he didn't...

That's why I wrote "HP spoiler" for the title! Unless there are crazy people who read the article though they know they haven't finished the book! Anyway, all articles on the Net which spoils books, movies, etc. all say "WARNING>>>Spoilers" So i thought it would be okay...O_O **Looks at coquina with wide, innocent eyes**

HARRY POTTER SPOILER...PLS DON"T READ IT IF YOU HAVEN FINISH THE BOOK!!! I don't know why J.K. Rowling always has to kill a character from book four onwards. After reading the book, my friends and I were going "ERM...we were like, so happy that they got the Horcrux and then, TADA, Dumby's dead, and the locket's gone." I know death is inevitable, but...why must there always be a guy who will die at the end of each book? It's like a death ritual or something. o_0

I don't know what you really mean by "strict", but if you are refering to the laws, then I think Singapore has the strictest laws. No gum allowed, no protests allowed, no smoking (in public places), no durians and gas cylinders on the train (each SG$5000), no indecent exposure (?!)... that's why Singapore is a fine city.

oh my god...i am sorry...! Didn't know he was called jacques......Didn't mean it, don't stare at me like that o_0