<p>Hey guys I'm new here. I'm taking the SAT Chemistry in 10 days and practicing solving questions right now. Came across these which I simply don't know how to do, although they seem extremely easy once you form the equation.</p>
<p>First one:</p>
<p>For the reaction of sodium with water, the balanced equation using the smallest whole numbers has which of the following coefficients?</p>
<p>I. 1
II. 2
III. 3</p>
<p>(A) I only (B) III only (C) I and II only (D) II and III only (E) I, II, and III</p>
<p>You have to set up the equation for sodium reacting with water to produce sodium hydroxide and hydrogen gas. Question is, you actually have to know how to set these equations up for the test (since, like on this question, it wasn't given)? How exactly do you do that? My book only talks about balancing equations, not setting them up. Yes, I know that a metal reacts with water to produce a base and H gas, but how do you properly plug in the coefficients?</p>
<p>Second one:</p>
<p>If 49 grams of H2SO4 react with 80.0 grams of NaOH, how much reactant will be left over after the reaction is complete?
(A) 24.5 g H2SO4 (B) none of either compound (C) 20. g NaOH (D) 40. g NaOH (E) 60. g NaOH</p>
<p>Once again, this problem requires you to set up an equation of H2SO4 reacting with sodium hydroxide to get water and sodium sulfate. The rest makes sense...but how do you form these equations?? :(
Thanks to anyone who tries to help!</p>
<ol>
<li><p>2Na + 2H2O -------------> 2Na(OH) + H2</p></li>
<li><p>H2(SO4) + 2Na(OH)--------------------> Na2(SO4) + 2H2O</p></li>
</ol>
<p>2nd reaction is called Neutralization Reaction. Remember, whenever acid and base react, salt and water are produced. </p>
<p>1st reaction is simple Redox reaction. </p>
<p>To form equations you need to remember the valencies of all ions which will form. just remember the electronic configuration.</p>
<p>Na - 1s2 2s2 2p6 3s1 - clearly only 1 electron can be removed from outer most shell (priciple qantum number, n, = 3) </p>
<p>SO4 goes to SO4 (-2) in ionic form and H -----> to H(+) similiarly, Na—>Na+ and OH-----> OH(-1). Remember OH is a complex radical and cannot be seperated into O and H respectively
Same goes for SO4</p>
<p>still doubt…ask me anytime.</p>
<p>Best of Luck</p>
<p>Thanks friend, I understand everything perfectly now. I really appreciate it.
Yeah, it makes sense, with those questions you need to know about the basics of acids/bases and redox reactions. </p>
<p>What I still don’t really understand about the first one is that how would I know the exact products formed? The products are sodium sulfate and hydrogen gas. Is this also basic knowledge of how bases form?</p>
<p>One other question: there were several other problems on the practice test and in the book where again, you have to write out the equations to begin solving the problem. Do you simply have to memorize specific chemical formulas for the test?</p>
<p>Find the weight of CaCO3 needed to produce 11.2 L CO2 when the calcium carbonate is reacted with hydrochloric acid. </p>
<p>When you write the formula, the products are CaCl2, H2O, and CO2. I know how to write the reactants, but how would I know what the products are? What am I supposed to do with these types of questions on the test? :(</p>
<p>H2(SO4) + 2Na(OH)--------------------> Na2(SO4) + 2H2O</p>
<p>Look, Hydrogen Sulphate dissociates into, 2H+ ions and 1 SO4(2-) ions. </p>
<p>Na(OH) ----> Na+ and (OH)-</p>
<p>now pairing the ions, H+ won’t go with Na+ as both have +ve charge on them. So only possible product for H+ is to react with (OH)- —> 2H and 1O ----> H20</p>
<p>Now, SO4 (2-) has 2 negative charge and to make it neutral, 2 positive charges are required.</p>
<p>Only 1 Na+ can’t be sufficient as still 1 -ve charge will be left so 2 Na+ will react with SO4 (2-) -----------> Na2(SO4).</p>
<p>CaCO3 + HCl -----------> CaCl2 + CO2 + H20</p>
<p>this is a acid+salt reaction.
always in this reaction, CO2 and H20 will be formed. Remember this.</p>
<p>If you know this then pair the remaining ions i.e - Ca and Cl. Ca----> Ca 2+ and Cl----> Cl-</p>
<p>therefore 2 Cl- will react to fullfill the electronic configuration of Ca.</p>
<p>:. CaCl2 will also be formed</p>
<p>These are very basic reactions and yo ought to have learned them by know.
Complex reactions like Redox reactions, Coordination Compound reactions will kill you if you have so much problem in these simple ones.</p>
<p>There are many reactions in transition elements (d-block) in which octets are expanded to allow anions than it may seem. Same goes for p block i.e PCl3, PCl5, PBr5, PBr7 are all formed. You can’t explain all of them on just formation of ions etc.</p>
<p>Also, organic chemistry reactions are also quite complex and you need to have understanding of co-ordinate reactions, inductive effect, Mesomeric effect, resonance, back bonding, hydrogen bonding, shifting of lone pairs, carbnanion, carbocation etc to understand them. </p>
<p>Many reactions take up whole of pages to understand. For example, procedure of Haloform reaction (CX3) is quite long if i remember correctly.</p>
<p>You have to study a lot more chemistry from now on. Organic chemistry is understanding based and you can’t cram all the reactions there. </p>
<p>I think that unless you are in class 8th, you are much behind your syllabus. So please study more not just for SAT but for you school clases, APs, IBs, Honourss.</p>
<p>Best of Luck for you SAT by the way.</p>