Chem. Help, pretty please?

<p>Ok, I'm not asking you to do my homework for me. In-fact, I have no homework. I just have a test tomorrow and I have absolutely no idea what I'm doing. </p>

<p>It's on predicting reaction products. Anyone know how to do this? Like, I need step by step sort of thing. </p>

<p>Here's just an example:</p>

<p>____ NaOH + ____ H2SO4 ---> ?</p>

<p>And also, the diff. types of a reactions. Anyone got a clue? Maybe some of you AP Chem'ers out there care to help out a struggling honors chem. student that already has an 86% in the class and can't afford to have it go any lower?</p>

<p>Thanks a bunch.</p>

<p>uh used your notes lol. And the periodic table.</p>

<p>khanacademy will tell you everything you need to know about this stuff.</p>

<p>well thanks, I found videos on balancing equations on khanacademy but not predicting reactions and the different types of reactions. God, I am so lost.</p>

<p>I haven’t taken chem in a year so I’m pretty rusty, but I’m attempting to be of some help since your test is tomorrow.</p>

<p>I definitely find that knowing the different types of reactions helps, such as combustion reactions vs single-replacement reactions vs double-replacement reactions. The example you gave above is a double-replacement reaction that results in H20 plus another substance because a base is reacting with an acid. The anions replace each other, and then you must balance out that equation. Studying the different types of reactions should be somewhat helpful, because you’ll be able to recognize them and predict the outcomes of chemical reactions.</p>

<p>I…don’t know how helpful that was since I didn’t just want to make it apply to that one example, but yeah. Being able to recognize the types of reactions, acids/bases, ionic compounds, etc. as well as being able to balance equations. will be helpful.</p>

<p>I PMed you, but I don’t know if it went through.</p>

<p>Unless I’m just completely screwing this up:</p>

<p>With NaOH and H2SO4 as products, you have a base and an acid. When these two things come together, they will form water and whatever is left over.</p>

<p>So…
NaOH + H2SO4 ----> H2O + Na2SO4 (unbalanced)
Keep in mind that the hydrogens typically stick to the water in the products. Also, make sure that your products’ (namely the sodium sulfate) charges are negated.</p>

<p>Then, balance the equation:
2NaOH + H2SO4 ----> 2H2O + Na2SO4</p>

<p>Wow, seriously? 5 posts on CC and no one helps out with a basic problem? </p>

<p>This is a strong acid- strong base
So you end up with
OH- + H+ ----> H2O</p>

<p>^ for net ionic</p>

<p>But there 3 H and 6 O… so it should be —> 2H2O that all i can remember.
Apperently you just organize the amount and try to balance it off</p>

<p>Edit:I didn’t see #7 post but he got it.</p>

<p>thanks guys. I just have one more question. When I’m doing a problem such as this:</p>

<p>____ PbSO4 + ____ AgNO3 -----> ?</p>

<p>Ok, I see that it’s a double replacement reaction. So for the first part of the product, I got </p>

<p>PbAg + …</p>

<p>What happens with the other part? Does it become SNO7 or something, because you’re supposed to combine the two anions…and in this case they happen to be polyatomic…??</p>

<p>EDIT: I just realised that I was doing that wrong. So would it be </p>

<p>PbNO3 + AgSO4</p>

<p>as the product?? How do I know which one to put first, the Ag or the SO (is this where the activity series comes into the picture?)…and since I’m supposed to change up the whole thing to their original “ionic properties” or whatever, how do I know which one to use? sulfite or sulfate?</p>

<p>PbNO3 + AgSO4</p>

<p>No. You combine cations with anions in reactions like this (and in almost all reactions you will probably do in your class). Just try thinking if your products even make any sense realistically when you’re doing problem as well. Do metals in real life usually just combine together? Only when you make special alloys and whatnot.</p>

<p>Yeah PbAg can’t be a product (fairly certain). It’s basically just switching the first element in the first compound with the first element in the second compound for a double replacement. I know there’s something you have to do with the charges, but I can’t remember that <.<. It’s been a few months or so since Chem.</p>

<p>Cation before anion in all cases I can think of</p>

<p>thanks!! so I was right? </p>

<p>PbSO4 + AgNO3 ----> PbNO3 + AgSO4?</p>

<p>Also, what about this case:</p>

<p>_____ HBr + ____ Fe -----> ?</p>

<p>I think I remember my teacher telling me that since this is a single replacement reaction, and one element has to be “kicked out”, this reaction is impossible, because Hydrogen and Bromine are in two different activity series (Br2 being in the activity of halogens and H2 being in the activity of metals)? Or is that not true for this particular problem because the H doesn’t have a subscript of 2 and the Br doesn’t have a subscript of 2? </p>

<p>So the product would be like HFe + Br?</p>

<p>That doesn’t really look right…</p>

<p>You combines the two cations again (All metals are positive ions when they are no longer just by themselves in a solid form). Also, as a general rule, adding an acid to a metal creates a metal salt (the metal cation bonded to an anion) and hydrogen gas (H2). Looking at this from a real life viewpoint again, acids are corrosive and if you think of any times in movies or something, pouring acids on metals makes a hissing noise and there is some bubbling or gas as the metal corrodes away. That is the hydrogen gas.</p>

<p>mmm…lol I’m still a little confused. So when I see a double replacement, and the anions are polyatomic ions, what am I supposed to do?</p>

<p>You usually just bond the poly atomic ions with the other cations. Polyatomic ions don’t usually change throughout the reaction. A nitrate or a sulfate will most likely still be a nitrate or sulfate at the end of the reaction.</p>

<p>You need an activity series chart to figure out single displacement. Which you could probably find on google images.</p>