How to do these CHEMISTRY problems ?!!

Test Preparation AP Sciences
1

<p>1.) What is the OH- concentration (M) of a solution that contains 5.00 x 10^-3 mole of H+ per liter?</p>

<p>2.) Which of the following solutions would show the greatest conductivity at 30 Celsius?
A. 0.20 M Ca(NO3)2
B. 0.25 M HCl
C. 0.30 M NaOH
D. 0.10 M NaCl
E. 0.40 M Ch3OH
(and can you explain your answer. THANKS!)</p>

<p>3.) Given the following compounds, arrange them in order of increasing acid strength:
AsH3 ---- HI ----- NaH ----- H2O</p>

<p>can you explain how??</p>

<p>DOES ANYONE KNOW HOW TO DO ANY OF THESE??</p>

2

<p>For number 2 I guess it’s asking which of the choices forms the strongest electrolyte, with the 30 degrees Celsius being a formality. I would say C, the sodium hydroxide, because it’s a strong base and at the highest concentration of the strong acids and bases, plus it’s soluble.</p>

<p>And for number 3 I think the HI would go at the end, because it’s a strong acid, though I don’t really know about the AsH3 or the NaH</p>

3

<p>Number 1, you are given molarity of H+ ions, which you can use to find the pH by using the formula pH = -log[H+]. From there, you can find pOH by using pH + pOH = 14. Then to find the molarity of OH-, just use pOH = -log[OH-].</p>

4

<p>I think number 2 is A.
Isn’t conductivity based on the vant hoff factor (the number of particles something dissociates into)? A dissolves into the most - 3 particles (1 CA and 2 NO3s).</p>

<p>For 3, I think NaH is first because NaOH would form, which is a strong base?</p>

5

<p>For number 1:</p>

<p>Kw=[H][OH]
1x10^-14=5x10^-3*[OH]
[OH]=2x10^-12</p>

<p>For number 2:</p>

<p>A, dissociates into the most anions</p>

<p>For number 3:</p>

<p>not too sure, sorry :(</p>

6

<p>for three i guess its in this order:
weakest acid to strongest acid
NaH, H2O, AsH3, HI
I’m not 100% sure though…</p>

7

<p>Omgsshh thanks!!!</p>

8

<p>wait so to find the vanhoff factor we just count the amount of molecules or something?</p>

9

<p>Why don’t you also look at the molarity of the total ion solution.</p>

<p>Don’t you have a total of .6 mol of ions in both CA(NO3)2 and .6 mol of ions in NaOH?</p>

10

<p>vant hoff factor (i) is based off the amount of ions that dissociate in aqueous solution. For nonelectrolytes, i = 1. For electrolytes, i = the number of ions that dissociate.</p>

<p>Example: CO2 : i = 1 ; NaCl : i = 2</p>

<p>Sometimes they’ll also ask you to calculate the vant hoff factor, given the other parts of the equation. In this case i will most likely not be a whole number (i is in reality only a whole number for strong electrolytes in small concentrations).</p>

<p>In addition, remember that this is important when raising the boiling point or lowering the freezing point. The larger the value of i, the more the BP is elevated or the FP depressed.</p>

<p>Cheers :).</p>

11

<p>ty bro. that was plain and simple.</p>

12

<p>Hey, you end up having .6 M of ions (.3 Na and .3 OH) for C</p>

<p>but also .6M of ions for A ( .2 Cu, .4 for NO3).</p>

<p>I asked my teacher, and he said to look at the mol of ions.</p>

<p>You have the same amount of mol so wouldn’t A and C be equal?</p>