<p>^ I normally use two decimal places in my calculations.
The table they give you gives two decimal places.</p>
<p>How do sig figs work with logs and ph and stuff like that?</p>
<p>And if i calculate the number of moles of something, and i know need to use that in the pv =nrt equation, so i round the moles to sig figs then plug it in the gas law, or do i use exact value from my calculatr</p>
<p>Also, how much work do you have to show? Is setup of equation and then final answer enough? Or do i have to show the actual manipulation, even though my calculator does it for me.</p>
<p>is -log([H])= 4.5 [H] = .000032 sufficient</p>
<p>or do i have to show [H] = 10^-4.5</p>
<p><a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board; (2005 Form B)</p>
<p>7.c)
I don’t understand this at all.
What happened to the equation listed in 7.b)?</p>
<p>When do you drop the variable if the difference is very small? </p>
<p>Like if the ICE chart says: 1.0x10^-14= (x)^2/(.01-x)</p>
<p>If you didn’t drop it, you would get a quadratic equation.
To simplify it you drop it.</p>
<p>Edit; Sorry, misread.
Someone earlier posted that their teacher said only drop it if the number is less than 10^-4.
I just assume that they want it dropped every time. . . so I just always drop it.</p>
<p>@Godzilla -
One has O2 and one has H20.
@ Abrayo - I think they call it that 5% rule?
Idk the details since I always just factor in everything.</p>
<p>Determine the empirical formula of a hydrocarbon that contains 85.7% carbon by mass…</p>
<p>could someone show me how they would do it? cause i did it right but i think i used up too much time the way i did it. thanks.</p>
<p>85.7 g of C, and 100-85.7g=14.3 g of H.
Divide both by their molar masses,
85.7/12.01 = about 7 moles.
14.3/1.008 = about 14.
This is a 1:2 ratio, so it’s CH2.</p>
<p>Did you get that?</p>
<p>@echoyjeff222: Thanks for writing that all up, but that wasn’t the part I was confused on (though it probably helped someone else). I just always second guess myself when I’m finding the pH in the various sections.</p>
<p>@guargum: Pretend then that you have 85.7 grams of carbon and 14.3 grams of hydrogen. You would then find the moles of each, and then divide both of them by the smaller number to get the subscripts. There is a chance that one of them will not be close enough to a whole number to round up (I’m not exactly sure what the rules are for that, I should look it up) and in that case you may have to multiply both of them by something.
Edit: You only round to whole numbers if it’s less than .1 or greater than .9</p>
<p>Does it matter how we draw the Lewis structures? I mean, can the bond angles be different from each other? </p>
<p>I always draw them correctly but my angles are always 20/30 degrees off</p>
<p>yeah i got CH2, but for some reason the way i did it is ridiculously long. i didn’t assume 87.5% to be 87.5g so that makes life easier. thanks a lot!</p>
<p>Also, what do you guys to for balancing the equations in Multiple Choice? I always get them wrong :(</p>
<p>I heard that most people use the matrix method. Not sure if that works by hand.</p>
<p>^ don’t even know what that is . . .
I balance it like normal? Not sure how to explain.</p>
<p>Solid calcium carbonate is added to a solution of ethanoic acid:
Why are the products CO2 + H2O? I put H+ + HCO3^1- (because in the past I saw not to put it as H2CO3 - unless that’s only for sulfuric acid?)</p>
<p>edit;
Sulfur trioxide gas is bubbled in sodium hydroxide.
Is it a rule of thumb that when you bubble a gas in a base, it produces H2O?</p>
<p><a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
5.c) is a mystery to me. . .
AgCl is a precipitate, right? What colour is it? White?</p>
<p>Anyone have any idea how to do this?
How can 100. mL of sodium hydroxide solution with a pH of 13.00 be converted to a sodium hydroxide solution with a pH of 12.00?</p>
<p>A) By diluting the solution with distilled water to a total volume of 108 mL
B) By diluting the solution with distilled water to a total volume of 200 mL
C) By diluting the solution with distilled water to a total volume of 1.00 L
D) By adding 100. mL of 0.10 M HCl
E) By adding 100. mL of 0.10 M NaOH</p>
<p>pH is logarithmic. Going from 13.00 to 12.00 is a difference of 1, but really a factor of 10.
So 10 times 100 ml = 1 L gives you what it has to turn out to be, which is C.</p>
<p>Can someone explain formal charge?</p>
<p>Formal charges are not tested.</p>
<p>It’s the number of valence electrons an atom should have (for example, 6 for oxygen) minus the number of electrons it has in the lewis dot diagram, but for each bond you only count 1 electron. You want it to be 0, or as small as possible, and if faced with two choices, the more negative formal charge should be on the more electronegative element.</p>