CHEMISTRY COMMUNITY

keyaluo4C

The half reactions for 6N.1 (a) are
Mn²⁺ + 2e- = Mn (s) E = -1.18 V
Ti²⁺ + 2e- = Ti (s) E = -1.63 V
Why does the answer key say that Ti is the one being reduced? Shouldn't it be Mn because TI has lower reduction potential?

keyaluo4C

To find the pH you need to first find [H⁺].
To find the concentration of H⁺ use the equation:
$E_{cell}=E_{cell}^{\circ}-\frac{0.0592 V}{n}\textup{logQ}$
Q in the equation is equal to $\frac{[Sn^{2+}]}{[H^{+}]^{2}}$
You would then solve for the concentration of H+ and then calculate pH.

keyaluo4C

You should be able to divide Kw by the concentration of H3O+ to get the same solution for the concentration of OH-. For (i) in the table you get a negative as the answer for pH but that should also be the correct pH. pH for (i) = -0.176.

keyaluo4C

For question 5J.11 we are predicting which way the equilibrium shifts with a temperature increase.
(b)X₂(g)⇌2X(g) where X is a halogen
The answer states that because the reaction is endothermic we know that it shifts towards products. How would we determine that this reaction is endothermic?

keyaluo4C

The question is: A sample of ammonium carbamate, NH4(NH2CO2), of mass 25.0 g was placed in an evacuated flask of volume 0.250 L and kept at 25 °C. At equilibrium, 17.4 mg of CO2 was present. What is the value of Kc for the decomposition of ammonium carbamate into ammonia and carbon dioxide? The reac...

keyaluo4C

I got pH=8.59

keyaluo4C

If K is the equilibrium constant and every species in the reaction is multiplied by n. The new K would be K^n. K1 is the constant of chemical equation 1, K2 of equation 2, K3 of equation 3: If eq1 + eq2 = eq3, K3 = K1 x K2 If (eq1 x n) + eq2 = eq 3, K3 = (K1^n) x K2 Remember to cancel out species th...

keyaluo4C

Yes.
Stotal=Ssys+Ssurr

keyaluo4C

The half-reaction for iron is actually Fe2+ -> Fe3+ + e-. Fe is being oxidized because it has a lower reduction potential.

keyaluo4C

I can't be sure what will appear on the final but we used Kw on the first test. A basic reaction and the pKa was given so you had to use Kb= Kw/Ka to find the Kb to solve the problem.

keyaluo4C

I have a different version of the test but I got the problem right. Could you post the full equation for the problem?

keyaluo4C

The reason you get 0.059 is because for some reason the solutions does not convert kj to j. If you convert kj to j in the beginning, you should get 0.59.

keyaluo4C

The outline doesn't really specify anything on electrolytic cells but since 6O is included in the homework problems I would mostly be concerned with the examples and homework problems.

keyaluo4C

Yes. In each half cell, reactants are first and products are last. Since the cell on the left is oxidizing, H2(g) would be before H+(aq).

keyaluo4C

The definition of an exothermic reaction is one that releases heat.

keyaluo4C

What is the reduction half-reaction for
$\textup{NO}^{-}_{2} \textup{(aq)}+ \textup{Al(s)}\rightarrow \textup{NH}_{3}\textup{(g)}+\textup{AlO}_{2}^{-}\textup{(aq)}$

keyaluo4C

For 6L.7: Write the half-reactions and devise a galvanic cell (write a cell diagram) to study each of the following reactions: (a) \textup{ArBr}_{(s)}\rightleftharpoons \textup{Ag}^{+}_{aq}+\textup{Br}^{-}_{aq} How do we determine which half-reaction is oxidation and which is reduction? Why ...

keyaluo4C

The example is: Engineers designing new piston engines and turbines need to understand how work and heat are involved in various compression and expansion cycles. Suppose that 1.00 mol of ideal gas molecules at an initial pressure of 3.00 atm and 292 K expands against a constant external pressure of...

keyaluo4C

Equation for change in entropy of an ideal gas when it expands isothermally:
$\Delta S = nR\textup{ln}\frac{P_{1}}{P_{2}}$

If initial pressure is greater than final pressure, $\Delta S$ is positive.

keyaluo4C

We are actually only measuring the changes in internal energy rather than the absolute value of the internal energy of the system.

keyaluo4C

1. Start with w: w=-P_{ex}\Delta V 2. Calculate \Delta V \Delta V=1.846L-0.345L=1.501L 3. Convert the given P_{ex} from Torr to atm P_{ex}=750 \textup{ torr } \times \frac{1 \textup{ atm}}{760 \textup{ Torr}}=.99\textup{ atm} 4. Plug into equation for w w=-.99 \times 1.5 =-1.49 \textup{L}\cdot \text...

keyaluo4C

Question 28 is naming the compound
Co(NH2CH2CH2NH2)2(CN)(Cl)]Cl

And the answer posted is chlorocyanobisethylenediamminecobalt (III) chloride.

Why would the Cl and CN ligands be put before the ethylenediamine ligand? Would en not be first by alphabetical order?

keyaluo4C

(From UA Lyndon Bui's Review)

Why is the oxidation state of the iron 2+? Shouldn't it be 4+?

keyaluo4C

You don't add -ate when naming. When anions end with -ate, you change the ending from -ate to -ato to name the complex (sulfate->sulfato).

keyaluo4C

Assume that the pH of the initial concentration of HCl is 1.0 mol/L. Since HCl is a strong acid the concentration of H3O+ is also 1.0 mol/L pH of initial concentration = - log (1.0) = 0.00. A dilution to 12% of the initial value would make the concentration of HCl and, in turn H3O+, 0.12 mol/L. pH o...

keyaluo4C

For sp2, when there are more than 3 valence electrons in the outer shell, three will hybridize and the rest will form pi bonds. This happens because it causes no leftover elections and is optimal.

keyaluo4C

Sig figs for pH are only calculated after the decimal. For example, a ph of 4.52 would have 2 sig figs.

keyaluo4C

They are put alphabetical order.

keyaluo4C

Yes, the acid is related to the conjugate base and the base is related to the conjugate acid.

keyaluo4C

How are electron affinity and electronegativity the same thing? I am having a hard time understanding how the energy gained from adding an electron is related to the tendency to attract electrons.

keyaluo4C

In the lecture guidelines, it says "Explain why lone pairs are more likely to be found in certain locations around a central atom." Is this actually referring to their location or is it just referring to how they affect bond angles?

keyaluo4C

What is the difference between angular nodes and radial nodes? When a question asks for how many nodal planes exist in a certain orbital should we be answering with angular nodes?

keyaluo4C

I find it easiest to think of it as shell, subshells, and orbitals.
Ex: n=2, l= 1
n = 2 means it is in the 2nd shell and l = 1 means it must be in the p orbital. There are 6 possible electrons in the 2p orbital.

keyaluo4C

There is a nodal plane in that area and the probability of finding an election in the nodal plane is 0.

keyaluo4C

Even when the molarity of a substance is given, sometimes the molarity used to calculate pH will be different because it is based on molarity of H3O+ and not the given molarity.

keyaluo4C

Yes, but it has to be the energy released after adding an electron to a neutral atom.

keyaluo4C

n- principal, represents the shell
l- orbital angular momentum, represents subshell in each shell
ml- magnetic, represents orbitals in subshell
ms- spin magnetic, spin state

keyaluo4C

If water is used as a solvent it can act as the base. Some strong acids in water can be weak in another solvent and vice versa.

keyaluo4C

You can't tell by the formula unless you memorize the strong acids and bases. If the Ka value is given, a larger Ka means a stronger acid.

keyaluo4C

How do you know what the ideal Lewis Structure is when there are many different ways of calculating the formal charge? Is it mostly trial and error?

keyaluo4C

Could someone explain the question #6 to me in UA Mr Ronald Yang's review problems and how he got to his solution again?

keyaluo4C

I can only get the answer to this question of 1.78E-31 m when I don't convert 92 miles to meters. Is this a mistake?

keyaluo4C

How would we write the shorthand electron configuration for noble gases?

keyaluo4C

1D.9 asks for the number of radial nodes and angular nodal surfaces. What is the difference between these two and aren't they the same number?

keyaluo4C

What is the difference between electronic transitions in atomic orbitals and molecular orbitals?

keyaluo4C

It is also important to keep in mind the kinetic energy of the ejected electron increases linearly with the frequency of the radiation.

keyaluo4C

The energy would be the kinetic energy of the electron (1/2mv^2).

keyaluo4C

In example 1B.3 on the textbook vers 7 the step 1 to the question is
E = 1/2 * (9.109E-31 kg) * (6.68E5 ms^-1)^2

Where did they get 9.109E-31? I understand 9.109E-31 kg is the mass but I don't know where the number is from.

keyaluo4C

Can someone explain this portion of the textbook to me? "When an electric current is passed through a low-pressure sample of hydrogen gas, the gas emits light. Hydrogen gas itself does not conduct electricity, but a strong electric field strips off electrons from the H2 molecules. As a result, ...

keyaluo4C

Yes, you would first have to convert nm to m which would make it v=(3x10^8 ms^-1)/(2.5x10^-9 m).

keyaluo4C

Yes, some of the particles would scatter because of the nucleus making the experiments significant because it was experimental evidence that all atoms have a nucleus.

keyaluo4C

The question is basically asking whether extremely dilute solutions can affect a person. To figure this out, it asks you to double the volume 90 times and see how many molecules are left in the final solution. We start by figuring out how many molecules are in 10 ml of solution. 10ml x .10mol/1000 m...

keyaluo4C

When I solve out G5 (b) I always end with 62.5 ml instead of 62.6 ml. Can someone explain why I can't seem to get the correct significant figures for this problem and what exactly you did to get it?

keyaluo4C

To expand, you would find the moles of Cl- by adding the moles of Cl from each of the compounds. To do this you would just divide the mass of each compound by the molar mass and you would not have to multiply by anything because there is only one in each.

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