SAT II Chem. questions??

Test Preparation SAT Subject Test Preparation
1

<p>Hello, I'm going to take the November Chemistry SAT Subject Test in a few days, and I'm taking practice tests. I'm using the Barron's Chem 11th Edition, and I was wondering about a few things:</p>

<ol>
<li><p>How can I write out an equation given only the reactants?
For example, for the question, “What mass of aluminum will be completely oxidized by 2 moles of oxygen at STP?”
You need the equation for the reaction, 4Al + 3O2 > 2Al2O3
Why not 'AlO2'? Is there a rule I'm missing?</p></li>
<li><p>For the question with: <a href="http://s27.postimg.org/dzurhma83/Screen_Shot_2014_11_04_at_4_07_42_pm.png"&gt;http://s27.postimg.org/dzurhma83/Screen_Shot_2014_11_04_at_4_07_42_pm.png&lt;/a>
as a reference, how do I identify the anode/cathode? Is Zinc commonly used as an anode?</p></li>
<li><p>For the question with: <a href="http://s10.postimg.org/ogx0p83rt/Screen_Shot_2014_11_04_at_4_11_46_pm.png"&gt;http://s10.postimg.org/ogx0p83rt/Screen_Shot_2014_11_04_at_4_11_46_pm.png&lt;/a> as a reference, and description:
“Recorded data:
Weight of U-tube................................ 20.36 g
Weight of U-tube and calcium chloride before................................................... 39.32 g
Weight of U-tube and calcium chloride after................................................... 57.32 g
Weight of boat and contents (copper oxide) before................................................... 30.23 g
Weight of boat and contents after................................................... 14.23 g
Weight of boat...................................................5.00 g
"
How would I solve this? (How could I come to a conclusion based upon this data?)</p></li>
<li><p>Final question:
If acetylene is a linear molecule with a triple bond between two carbons, wouldn't the hybrid orbital be sp2? C2H2 has no lone pairs, either, so wouldn't it be a trigonal planar with bond angles of 120?</p></li>
</ol>

<p>Thank you so much!!!</p>

2

<p>1: Valency. Al is +3 and O is -2 so the normal product would be Al2O3.</p>

<ol>
<li>AnOx, RedCat.
Anode = Oxidation.
Cathode = Reduction.
^Those are by definition. Write out the half reaction and see if it’s oxidation or reduction, which in turn will decide if it’s the anode or cathode.</li>
</ol>

<p>To determine that you’ll probably need to know the reactivity series (Zn is more reactive than CU so Zn will reduce Cu). If Cu was replaced by something more reactive than Zn, then Zn would be reduced.</p>

<ol>
<li>That setup is pretty easy to figure out just by looking at it.
-Zn displaces H in HCl, evolving H2.
-H2 (and some air in the flask) move through the drying tube, the CaCl2 removes any moisture in the air.
-H2 reaches the boat and reacts with O2 (H displaces Cu) forming H2O.
-H2O gets absorbed by the CaCl2 in the u-tube, accounting for the additional mass.</li>
</ol>

<p>The change in mass of the boat will give you moles of oxygen. u-tube data gives you mass of water. Plenty of ways to figure out the mass ratio between H and O in water.</p>

<ol>
<li>Triple bonds are sp hybridized (double bonds are sp2). As you said, there are only 2 things about one of the carbon atoms: the other carbon atom and a hydrogen atom (no lone pairs) so naturally they’d align themselves as far away from each other as possible. ie: Linear, 180 degrees.</li>
</ol>

3

<p>Thanks lostint!</p>