rasen58

Can I connect my DC motor straight to a 9V battery? or do I need a resistor in between? I've tried it and the motor spins, but will having no resistor ruin the motor? Also, when I connect the two wires to complete the circuit, I see small sparks, is that normal?

Oh, that makes sense now. But do you only look at the relative amounts of the anion? Because for #5, there are 3 mol of the Na ion and 3 mol of the CrO4 ion right? So do you only consider the anion because there is only 1 mol of the Pb to make PbCrO4?

So I did #4 correctly because I predicted that they would mix and produce PbCrO4 and NaNO3. So that means that an insoluble yellow solid and a soluble white solid would be produced. So I picked A - Yellow solid and colorless solution, which is correct. But for #5 and 6, I don't understand how to use the amount of moles to determine which is produced. I made the balanced equation for 5, but the coefficients for each product and reactant are 1, so I don't see how the moles change.

The pH of a 0.10 M solution of an aqueous weak acid (HA) is 4.00. The Ka for the weak acid is..... I know the expression for Ka is [H+][A-]/[HA] But I don't know what to do next.

The question is find the temperature for the normal boiling point in the phase diagram of the pure substance above. I thought the answer would be 90 C because that is where the liquid/gas line hits 1 atm. But apparently the answer is 44 C. Why?

But even if I did Cu2+ + 3I- -> CuI + I2 it would still be wrong, but why is it wrong?

So are ion pairs not bonded?

What is the structure of NH4OH? The only google image result I got was this, but that doens't seem possible because the H has two bonds.

The question was to balance this equation What I did was Cu2+ + 2I- -> CuI + I2 But the answer is 2 Cu2+ + 4I- -> 2CuI + I2 So do 2 moles of ions of an element combine to make 1 mole of that element? Is that what I was missing?

Wow. I totally forgot about the VCC. That was stupid of me. Thank you.

If a digital inverter (like the 7404 chip) can turn a 0 into a 1, why can't that be used to make infinite energy? Why can't you just have it always outputting a digital high? Also, how is it possible for something to create energy like that?

Sorry, I worded my question wrong. I meant the actual answer is +5, but I thought it was just -1 So why is it +5?

What is the oxidation state of the polyatomic ion in the compound Mg(NO3)2 A. +2 B -2 C -1 D +5 E +6 The polyatomic ion is NO3, and I already knew the oxidation state of that nitrate is -1, so I thought the answer was actually +5. How is the oxidation state even a positive number and how is it +5 because NO3 is an anion, so it should be negative anyway.

The volume of a sample of oxygen is 300 mL when the pressure is 1 atm and the temperature is 27 C. At what Celsius temperature is the volume 1 L and the pressure .500 atm? a. 22 C b. 45 C c. .5 K d. 227 C I used the combined gas law and set up the proportion of PV/T (1 x 300 m)/27 = (.5 x 1000 m)/x I solved for x (the temperature) and got 45, but the answer is 227. What did I do wrong?

Oh I see now. I did the calculation wrong. The molar mass is actually 78, which is the same as D. Thank you!

The molar heat of vaporization for a certain compound is 30.8 kJ/mol. If 0.770 kJ were required to vaporize 1.95 g of the compound, its molecular formula could be a. C3H6 b. C4H10 c. C5H10 d. C6H6 e. C7H14 I tried using the formula q = Hvap x (mass/molar mass) and plugged in the numbers so .770 kJ = 30.8 kJ/mol x 1.95 g/molar mass Solving for the molar mass, I got .0128. What should I do after that?

1. A discharged lithium-ion battery is constructed using a thin slice of graphite as anode, a piece of porous polypropylene sheet as separator, and a thin piece of lithium cobalt oxide as cathode. The dimensions of the anode, separator, and cathode are 1 cm x 2 cm x 50 microns, 1 cm x 2 cm x 25 microns, and 1 cm x 2 cm x 50 microns, respectively. When charging the battery, lithium ions deintercalate from the cathode and intercalate into the anode. Once the battery is fully charged, the anode has expanded by 10% in volume, and the cathode has expanded by 20% in volume. Assuming the overall volume of the battery is held constant, calculate the percentage in volume change for the separator. Since the separator is porous, what does this mean to the pores and the ability for lithium ions to pass through these pores? So the anode is 100 x 10-10 and separator is 50 x 10-10 and cathode is 100 x 10-10 Total Volume = 250 x 10-10 Anode becomes 110, cathode becomes 120, so separator has to decrease to 20, so it decreases by 60% I'm just not sure about the question about what happens to the pores and the lithium ions. Do the pores become smaller and the ions cannot pass through anymore? But that wouldn't make sense because they need to pass through to discharge. 2. Due to space constraints, one of the battery packs is placed next to the internal combustion engine and separated by 2 cm of foam insulation. During maximum power, the outside surface temperature of the engine can reach 220°C. If the highest temperature that the battery can experience is 120°C before going unstable, are the current placements of the battery pack and the engine safe? The heat transfer rate through the insulation is 720 W/m2, and the thermal conductivity of the insulation is 0.12 W/m °C I think the answer is no because 220 is a lot more than 120, but how do I use the heat transfer rate and thermal conductivity to help me do the problem?

I found 2 ATP + glucose + 4 ADP + 2 Pi + 2 NAD+ 2 ADP + 2 pyruvate + 4 ATP + 2 NADH Then I tried plugging in the numbers from the problem, but I'm not sure what to do after that

A yeast extract contains all the enzymes required for alcohol production. The extract is incubated under anaerobic conditions in 1 liter of media containing: 200 mM glucose, 20 mM ADP, 40 mM ATP, 2 mM NADH, 2mM NAD+, and 20 mM Pi (inorganic phosphates). What is the max amount of ethanol that can be produced in these conditions? I have no idea what to do at all for this problem. Is there an equation for ethanol production?

10.0 g of Zn powder is added into a solution of silver nitrate, AgNO3. The total mass of the metallic solid recovered at the end of the reaction is 12.32 g. Assuming that the reaction did not go to completion, how many grams of Zn did react? So the equation I got what Zn (s) + 2AgNO3 (aq) -> 2Ag (s) + Zn(NO3)2 (s) I think the zinc nitrate is solid because the question asks about a metallic solid. Then, 12.32 g X 1 mol/189.41 g Zn(NO3)2 = .065 mol Zn(NO3)2 Then to find the original Zn, .065 mol X 1 mol Zn/1mol Zn(NO3)2 = .065 mol Zn .065 mol Zn X 65.39 g/1 mol = 4.25 g Zn But the answer should be 1 g Zn. What did I do wrong?

I got it now. Thanks everyone!

Sensei, it actually helped a lot! It helped me to figure out the way to do it without molecules. Thanks a lot! hypervalent_iodine, I'm still not sure what to do next. How would I find the molar mass from 1 g and .0367 moles?

Thanks Sensei! hypervalent_iodine How would I do it while in staying in moles? So I did 3.9 g Cl x 1 mol Cl/35.45 g Cl = .11 mol Cl Because the formula unit is MCl3, .11 mol Cl x 1 mol M/3 mol Cl = .0367 mol M But then what do I do from there to get the mass of M?

So M bonds to 3 cloride ions (MCl3), but how do I figure out how many moles of M are in the 1 g?

Ohh, I see! Thank you!