SAT Chemistry questions help please

Test Preparation SAT Subject Test Preparation
1

<p>so…i am confused</p>

<p>Which of the following does NOT react with a dilute sulfuric acid solution H2SO4?</p>

<li>NaNO3, Na2S, Na3PO4, Na2CO3, NaOH.
The answer is NaNO3; please give an explanation why, and explanations for the other ones.</li>
</ol>

<p>…AlCl3(aq)+…NH3(aq)+…H20 —></p>

<p>Which of the following is one of the products obtained from the reaction above?

  1. AlN, AlH3, Al, Al(NO3)3, Al(OH)3. The answer is Al(OH)3. Why?</p>

<p>I haven’t taken a real chemistry class so I have trouble with reactions.
Thanks!</p>

2

<p>1.) NaNO3 is a neutral salt, (a combination of two weak conjugate acids/bases). Therefore, it won't react to an acidic solution like the other salts will.</p>

<p>not too sure about the reaction one actually :( sorry...</p>

3

<p>Na2S forms Na+ and S2- ions. S2- ions react with H+ ions to form H2 gas.
Na3PO4 forms Na+ and PO43- ions. PO43- reacts with H+ to form H3PO4, which is a weak electrolyte (doesn't fully dissociate).
Na2CO3 forms Na+ and CO32-. CO32- reacts with H+ to form H2CO3, which then decomposes into H20 and CO2.
NaOH is a base, which reacts with an acid to form water, releasing energy.</p>

4

<p>Forizzlejdl's reasoning is not correct. Both products of the reaction between H2SO4 and NaNO3 are soluble (HNO3 + Na2SO4), which means that your reactants are the same as your products. No reaction has occurred.</p>

<p>Hebrewhammer is correct with the remaining explanations, except that in the reaction with Na2S, it forms H2S gas, not H2 gas.</p>

<p>For the second part, you have to recognize that in this reaction, NH3 acts as a base and H2O as an acid. The NH3 will react with water to produce OH- and NH4+. The OH- will react with the Al(3+) in solution, giving Al(OH)3. Al(OH)3, aka aluminum hydroxide, is insoluble. The other product of this reaction would be NH4Cl, which is a soluble salt. The net ionic equation would be:</p>

<p>Al(3+) + 3NH3 + 3H2O --> Al(OH)3 + 3NH4(+)</p>

5

<p>But goldshadow what about naoh, if u r right then naoh+h2so4 gives na2so4 and h20 which r both soluble and they disassociate.? then it should mean the rxn should not take place??</p>

6

<p>The reaction does take place; H2O is what the reaction is taking place in and does not dissociate. In other words, the net ionic equation is:</p>

<p>OH(-) + H(+)--> H2O</p>

<p>I think I understand what you're saying... that H2O should "dissociate" into H+ and OH-. However, you have to realize that only a tiny fraction of water is in that form at any one time; it is not an ionic salt that "fully dissociates". In fact, the vast majority of it won't dissociate because the reaction itself is taking place in water. Unlike an ionic salt such as NaCl, or NaOH, which will completely dissociate (for SAT chemistry purposes) in water.</p>

<p>So in other words, only a tiny fraction of water is found as hydronium and hydroxide, while nearly all of it is found as H2O.</p>

7

<p>ok that was great explanation. Thankx</p>

8

<p>Well put, goldshadow. That explanation was really interesting.</p>