<p>They’re usually a couple in multiple choice and not more than once in Question 4 in MC.</p>
<p>I haven’t done any outside prep so I don’t know any about review books; only past exams.</p>
<p>Gee, I wish I was as confident about this test as you Niquii77! “Haven’t done any outside prep…” I can only dream of being like that in chemistry XD</p>
<p>I just took a practice multiple choice and got 62% of the questions… Hopefully this is a good sign! I would love to be able to work my way up to a 5 by the end of this week.</p>
<p>@thelemonisinplay My teacher told me today that if you get approximately 67 percent of the multiple choice right, you will most likely get a 3 or better. That doesnt include free response, so if you do really well on that part and get 2/3 of the mc correct, you can probably get a 4 or a 5.</p>
<p>@lemon You’re making me blush! Lol. I’m confident through the practice that my teacher has put my class through. Once you get comfortable, you’re able to see where your strengths and weaknesses lie. It’s great that you were able to take a multiple choice and a 62% is definitely within the four range if you do as well or better on the free response! Don’t doubt yourself!</p>
<p>thelemonisinplay, 5 steps to a 5 is great. I used barron’s at first because it’s really comprehensive and my teacher tends to skip over things without knowing it so i used that. Now i’m using 5 steps to a 5 as a review for this week and it’s really good! I really recommend it… especially the last chapter, where it has an outline of all 22 AP recommended labs. It also covered some things that barron’s didnt go over in a less formal fashion, and I liked that cause it was easier to understand</p>
<p>Can anyone help me out with this question?
Sodium sulfate forms a number of hydrates. A sample of a hydrate is heated until all the water is removed. What is the formula of the original hydrate if it loses 56% of its mass when heated?
Na2SO4 10 H20
NA2SO4 1 H20
NA2SO4 3 H20
NA2SO4 6 H20
NA2SO4 8 H20</p>
<p>Explaination would be great, thanks!</p>
<p>The sample loses 56% of its mass. Assume you start with 100 g of the sample (this assumption is useful for many stoich problems when you’re given a percentage). Therefore, it loses 56 g of water.
Convert grams to moles for water: 56 g / 18.016 g/mol = 3.1083 mol water
If the sample lost 56g, the remaining 100-56 = 44 g must be the sodium sulfate by itself.
Convert grams to moles for Na2SO4: 44 g / 142.04 g/mol = 0.30977 mol Na2SO4
Then determine the formula by simplifying the mole ratio:
3.1083 mol H2O / 0.30977 mol = ~10 mol H2O
0.30977 mol Na2SO4 / 0.30977 mol = 1 mol Na2SO4
Therefore, the formula is Na2SO4*10H2O.</p>
<p>Background info:
Hydrates are compounds that contain water as a part of their structure in a certain ratio (for example, glucose molecules have carbon and water in a 1:1 ratio). If you get rid of the water (heating it up) the substance is known as anhydrous. It must be kept in something called a desiccator or else water will go back in.</p>
<p>So for this problem it looks like you need to find the molar mass of the various hydrates (the 5 answer choices) and the molar mass of the anhydrous compound (sodium sulfate without any H2Os attached). 56% of the hydrate’s molar mass is eliminated so the original anhydrous compound must have a molar mass of 44% of the hydrate’s. So calculate 44% of the molar mass of the various hydrates. The hydrate in which 44% of its molar mass is equal to the molar mass of anhydrous sodium sulfate will be the answer.</p>
<p>edit: fixed error.</p>
<p>Helpful hint for the MC:
If you’re struggling with doing the calculations without a calculator, the key to this section is estimation. For example, if you’re given 52 grams, or 1013 kJ/mol, why use those when you can use 50 grams or 1000 kJ/mol? This will make the math immensely less annoying. The answer choices tend to be sufficiently far apart such that your estimations won’t cause you to lose much accuracy.</p>
<p>You should also review how to do scientific notation calculations by hand if you aren’t sure on those.</p>
<p>Can someone explain to me how to determine relative density of each phase from the phase diagram? thanks!</p>
<p>Solids are the most dense, then liquids, and last, gases. If that’s what you mean…?</p>
<p>Unless you mean specific gravity and density…but those are with numbers…</p>
<p>Do we have to know specific gravity for the test? Also, do we need to memorize the equations for freezing point depression and boiling point?</p>
<p>So what are your/your teachers predictions on FR?
Mine says solutions and kinetics and she wants electro but says probably not</p>
<p>My teacher keeps saying kinetics and equilibrium but that’s already guaranteed. I just really hope it’s electro/kinetics/equilibrium and not something like molecular structure because that’s all memorizing and annoying and ugh</p>
<p>Yeah, my teacher’s been saying the same thing. The 1st free response will be some form of an equilibrium question. Apparently one of the calculator FRQ’s is going to be a lab data question… I really really hope we have an electrochem question!! And please no bonding. I can’t do bonding to save my life…</p>
<p>i’m spending this entire weekend memorizing molecular geometry and bond angles ugh. if we have an electrochem question that’s just like “find this Ecell” or “is this reaction spontaneous” i will cry of happiness</p>
<p>I hope we have IMF and gases like PV=nRT! That stuff is great. I have to memorize all my molecular geometry too. I think I can do fine on kinetics, but if we have acid/base and buffers I will cry.</p>
<p>Oh and if anyone’s nervous, we had a student who took AP Chem last year talk to us. He did all the problems, but only had enough time to fill in 35ish onto his scantron. He ended up getting a 4.</p>
<p>I’m not trying to be that guy…but</p>
<p>Let’s say that he did get 100% out of the 35 that he did answer correct. That’s a 46% which is only worth 45% of your overall grade. I can guarantee you that he did not get a 46% on the rest of his exam. You cannot “bomb” your MC and go into FRQ with the same mentality and get a 4. </p>
<p>Just sayin’.</p>
<p>If we have buffers, I will literally burst into tears during the exam. I still don’t completely understand partial pressures. How exactly do you solve for a specific partial pressure? I always miss MC questions involving pressure.</p>