How to make a qualitative analysis for carbonate ions?

"Design a qualitative analysis for carbonate ions, using a reactant that would not precipitate sulphide ions in the sample. Write a net ionic equation for the precipitation reaction."

That's the question from the lab. I think we have two solutions: one with carbonate ions and the other with sulphide ions. We have to add one solution to both of these that would create a precipitate in the Carbonate but not the sulphide. Only I have no idea what the solutions would be.

What are the three solutions, or what could they be?

Answer: 
Calcium carbonate is insoluble but calcium sulfide is soluble. So if you add a solution of, say, calcium chloride to each, you'd precipitate CaCO3 in one solution, but would not ppt CaS in the other. Ca^+2(aq) + CO3^-2(aq) ---> CaCO3(s)

How to solve a mole fraction problem given the example?

A sample of C2H2 (g) has a pressure of 8.2 kPa. After some time a portion of it reacts to form C6H6 (g). The total pressure of the mixture of gases is then 4.4 kPa. Assume the volume and the temperature do not change. Find the mole fraction of C2H2 (g) that has undergone reaction.
If you may please explain your steps in getting to the solution, that would help me understand the problem so I can solve similar ones.
I need the actual percent value of C2H2 that has undergone reaction.

Answer: 
Start with the ideal gas law PV=nRT Initially P1 = 8.2 kPa and n1 = moles of C2H2 (no C6H6) After the reaction P2 = 4.4 kPa and n2 = moles of C2H2 + moles of C6H6 Since T1 = T2 and V1 = V2 and R is R, dividing the 2 equations results in... P2 / P1 = n2 / n1 now we know that 3 moles of C2H2 will react to form 1 mole of C6H6 if we let x = the extent of reaction or the amount of C6H6 produced then we know that the final moles of C2H2 = n1 - 3*x so... the total moles of gas mixture in the final gas (n2) = x + n1 - 3x or simplified to n2 = n1 - 2x substitute back into P2 / P1 = n2 / n1 and assume a basis of n1 = 1 mole (its arbitrary because you are just looking for mole fractions), then simplify the equation and solve for x the resulting fraction of C2H2 that underwent the reaction is (initial C2H2 - final C2H2) / intial C2H2 or (n1 - (n1 - 3x))/n1 or 3x / n1

How to tell if a reaction is exothermic or endothermic?

I know that exothermic reactions are negative and are on the product side, and endothermic are positive and are on the reactant side. But I still can't grasp it, can someone show some examples of this in chemical equations?

Answer: 
exothermic releases heat or energy. endothermic reactions accept heat or energy.

How to tell when a double replacement reaction will occur?

In my beginning chemistry class, I am supposed to predict reactions between aqueous solutions. I know that a reaction occurs if a partially soluble gas forms, a weak electrolyte is formed, or a solid precipitate is formed but I'm still having a hard time determining if a reaction will occur at all. Can anyone help me understand the rules for double replacement reactions?

Answer: 
You've got the principles down--formation of water, a gas, or a precipitate. The next thing is to learn what salts are water-soluble and -insolube.

How to tell if organic chemicals are correctly named?

How do you tell if organic chemicals are correctly named?
For example, "methene" and "2-ethylheptane" are incorrectly named, and they don't exist. How come?

Answer: 
"ene" means a double bond between two carbons. But "meth" means only one carbon. So there can be no methene. You have to use the longest chain. If you draw it out, you will find that "2-ethylheptane" is really 3-methyloctane. 8 is longer than 7.

How to know the order of the elements in a molecular compound and how to write the formula?

For example, given two elements, such as carbon and oxygen, how would you know which order to put the elements in? Regarding the formula, I'm pretty sure there are multiple possibilities, such as CO and CO2.
Thank-you!

Answer: 
The order of the elements depends on the types of elements and their electronegativities. For a simple compound of a metal and nonmetal, the metal always goes first. This follows the more general rule that the element with lower electronegativity is written first, followed by the element with the greater electronegativity. This is applicable to compounds of two nonmetals. C and O are both nonmetals, and O has a greater electronegativity, so it is written second, and the carbon comes first. As for the subscripts in the formulas, those are determined from the oxidation numbers of the elements. Each element exhibits one or more oxidation numbers which give the ratio of the elements in a compound. For instance, O is always assigned an oxidation number of -2. Carbon frequently has oxidation numbers of +2 and +4. The sum of the oxidation numbers for a compound will always add up to zero. So if C is exhibiting an oxidation number of +2 and oxygen is -2, then we need only one of each to make CO. If carbon is exhibiting an oxidation number of +4, then two oxygen atoms are needed to make the sum zero, and we get CO2. You can find a table of common oxidation numbers here: http://www.thecatalyst.org/oxnotabl.html

How to figure out electron configuration by looking at the periodic table?

Yea. My school basically teaches you how to graph and pick your butthole.

Answer: 
I am not trying to be funny - here is your answer: http://en.wikipedia.org/wiki/Aufbau_principle

How to store current in a circuit having electron flow ?

I am making an experiment and the result is flow of electrons.
how can i collect the electric current ?
please give me a detailed explanation....... .

Answer: 
You could charge a battery. You could charge a capacitor. Flash attachments for film cameras used this kind of circuit. The light needed more electricity than a battery could provide instantaneously. So the battery would be used to charge a capacitor over time. The photographer might have to wait 20 seconds between shots for the capacitors to charge up again. Do you need to store the current? or do you just need to measure how much current was produced?

How to know how many significant figures to use in an answer?

If the numbers in the question use 4 sig figs, but the calculation involves a number (in between steps) that is 2 sig fig. Would the answer be 4 or 2 sig figs?

And do you look at the sig figs for ALL the numbers in the calculations? Or just the last calculation?

Answer: 
It really depends on the type of mathematical operation you are performing. If you are multiplying or dividing, then yes, the final answer would be 2 sig figs. However, if you are adding or subtracting then it is likely that you will retain the 4 sig figs and your answer would properly be given in 4 sig figs. Without a problem to see it is not possible to give you a specific answer. Hope this is helpful to you. JIL HIR

How to calculate the volume of a solution?

If 250 grams of magnesium nitrate was used to prepare a 0.550mol/L solution, what is the volume of the resulting solution?

Answer: 
250g x ( 1 mole Mg(NO3)2 / 148.3g Mg(NO3)2) x (1 L / 0.550 mol Mg(NO3)2) = 3.1L solution

Syndicate content