Can you guys give me a clue in how to approach this problem?
Commercial brass,an alloy of Zn and Cu,reacts with Hydrochloric acid as follows:
Zn+2HCL-->ZnCl2+H2
(Cu does not reacts with HCL)When.0565g of a certain brass alloy is reacted with excess HCL,.0985g ZnCl2 is eventually isolated.
a.What is the composition of the brass by mass?
b.How could this result be checked without changing the above procedure?
I have tried converting .0985g to moles of Zn but then I do not know what to do? To be honest I don't get the question. Thanks in advance for your help.
You need to determine the percent composition of Zn in ZnCl2 based on atomic masses and the formula. Then, you can get the grams of Zn recovered.
This doesn't change Bob Pursley's answer but let me try to help so you will "get the question." The idea in any analytical scheme is to start with a known mass of substance and convert it to something else that is known. You started with brass and converted the Zn in the brass to ZnCl2. Then the ZnCl2 was weighed. Grams ZnCl2 can be converted to mols Zn and to grams Zn and (g Zn/g sample)*100 = %Zn. The idea is to work backwards from what you can weigh to determine how much of a material you MUST have started with. For the second part, think about this as a hint:
What else is produced in addition to the ZnCl2 and how might you use that to determine the amount of Zn in the brass alloy?
I'm sorry to be such a big bother but I just want to make sure I did it the right way.
(.0985gZnCl2)(1molZnCl2)/(136.28gZnCl2)
I got(7.23times10withthe exponent-4 mols)
Then I converted moles of ZnCl2 to mol of Zn using themole to mole ratio. Then I converted moles of Zn to grams, and then I didvided the mass of Zn by the mass of ZnCl and times it by a hundred. And I got .03468 (which I think is a very small number), then I multiply the mass in the reactant side .5065g by the percentage which was (3.4times10exponent-4) (igot this by dividing .03468 by 100).
My final answer was (1.7568times10 exponent-4) I will really appreciate If you tell If I'm right, I'm a little unconfident in regard to the answer because is such a small number. Thank you again in advance. Also thank you very much both bobpursleyand Drbob222, your answers where as you might already know very helpfull.
use stoich to convert into grams of Zn then find percentage like normal
To approach this problem, you need to use the concept of stoichiometry. Stoichiometry is a branch of chemistry that deals with the quantitative relationships between reactants and products in chemical reactions.
We are given that Zn reacts with HCl to form ZnCl2, and that Cu does not react with HCl. We are also given the masses of ZnCl2 and the brass alloy.
a. To determine the composition of the brass alloy by mass, you need to find the mass of Zn and Cu in the alloy. Here's how you can do that:
1. Calculate the moles of ZnCl2 using the molar mass of ZnCl2 (Zn: 65.38 g/mol, Cl: 35.45 g/mol). Divide the mass of ZnCl2 (0.0985 g) by its molar mass to get the number of moles.
2. According to the balanced equation, 1 mole of ZnCl2 is formed from 1 mole of Zn. Therefore, the moles of Zn present in the ZnCl2 is the same as the moles of ZnCl2.
3. Now, using the molar ratio from the balanced equation, determine the moles of Zn in the brass alloy. Multiply the moles of ZnCl2 by the molar ratio of Zn to ZnCl2 (1 mole Zn / 1 mole ZnCl2) to get the moles of Zn in the alloy.
4. Calculate the mass of Zn in the alloy by multiplying the moles of Zn by the molar mass of Zn (65.38 g/mol).
5. To find the mass of Cu in the alloy, subtract the mass of Zn from the total mass of the alloy. The composition of the brass alloy by mass is now determined.
b. To check the result without changing the procedure, you can use a different method to determine the composition of the alloy. One way to do this is by using an analytical technique such as atomic absorption spectroscopy (AAS). AAS can be used to quantitatively determine the concentration of different elements in a sample, including Cu and Zn. By comparing the results obtained from AAS with the composition calculated in part a, you can verify the accuracy of your findings.
By following these steps, you should be able to solve the problem and find the composition of the brass alloy by mass.