For many years the recovery of gold-that is, the seperation of gold from other materials-involved the use of potassium cyanide:
4AU + 8KCN + 02 +2H20 -> 4KAu(CN)2 + 4KOH
What is the minimum amount of KCN in moles needed to extract 29.0 g (about an ounce) of gold?
Now my question is one of the proper equations as I don't know what symbol to use for which quantity...
I understand that
mass = (molecular mass)(moles of mass)
were mass has units of grams, g, symbol used curvy M, mass of each element in the compound times subscripts of the element i.e. C2 would be 2(12.00g) = 24.00 g
mole of mass is the coeficent before the compound in the balanced reaction equation
m = Mn
I then would go to use subscripts were if the question asked about a compound on in part of the reactant balanced equation I would just use a R for a subscript and a Y for yield
now this problem bothers me
dividing the equation above by Mn I get
m/(Mn) = 1
and then go do the problem but sense the question is making reference to two reactants I had to use A and B for subscripts as well were A is the gold compound and B is the KCN compound
(m_R_A)/( (M_R_A)(n_R_A) ) = (m_R_B)/( (M_R_B)(n_R_B) )
solving for m_R_B
( (m_R_A)(M_R_B)(n_R_B) )/( (M_R_B)(n_R_B) ) = m_R_B
now my probelm is that I know that m_R_A is given in the problem 29.0 g so I now that m = Mn solving for n I get m/M I need to solve for n so clearly then
(m_R_B)/(M_R_B) = n_R_B = ( (m_R_A)(n_R_B) )/( (M_R_B)(n_R_B) )
clearly my use of symbols is wrong but it makes sense were n_R_B is the is the 8 and also what the probelm is asking for me clearly a probelm but here is what I did
( (29.0 g Au)(8 mol KCN) )/( (197.0 (g Au)/(mol Au))(4 mol Au) ) = .294 mol KCN
clearly this is a probelm even though its write because in the equation I said that KCN was 8 moles but when I solved I got .294 mol KCN are these two different values because they are both the amount of moles of KCN
I'm kind of confused please let me know how to make sense of this in my equation and understand how they are different and the symbols I should use to indicate so as I don't know how to do this please let me know if you don't understand
Frankly, I understood only a sentence or two of your post. Poor punctuation and run on sentences was partly to blame (as well as spelling where as were); however, some of the problem just escapes me. I think you have made it far to complicated. Here is how you do the problem.
mols Au in 29.0 g Au =
moles = grams/molar mass = 29.0/196.97 = 0.147 moles Au.
Now convert moles Au to mols KCN using the coefficients in the balanced equation.
0.147 moles Au x (8 moles KCN/4 moles Au) = 0.147 x 2 = 0.294 moles KCN.
I sense you are confused that the moles KCN should be 8 moles while you obtained 0.294 moles. The 0.294 mole KCN is the correct answer when 29.0 g Au is separated; the 8 moles KCN is the correct answer when 4*197.9 g Au (4 moles Au) is separated.
Well, it seems like you have quite a bit of confusion going on there! Let me try to help you out with the symbols and equations.
First, let's establish some symbols:
- m_Au = mass of gold
- M_Au = molar mass of gold
- n_Au = moles of gold
- m_KCN = mass of potassium cyanide
- M_KCN = molar mass of potassium cyanide
- n_KCN = moles of potassium cyanide
Next, we can use the equation you provided to find the moles of gold:
m_Au = n_Au * M_Au
Solving for n_Au, we get:
n_Au = m_Au / M_Au
Now, let's consider the equation for the reaction:
4Au + 8KCN + O2 + 2H2O -> 4KAu(CN)2 + 4KOH
We can see that the mole ratio between gold (Au) and potassium cyanide (KCN) is 1:2. So, if we have n_Au moles of gold, we would need 2 * n_Au moles of KCN.
Applying this to your problem, substituting in the given values:
n_KCN = 2 * n_Au = 2 * (29.0 g Au / M_Au)
To find the moles of KCN, you need to know the molar mass of gold (M_Au). Once you have that, you can calculate n_KCN using the formula above.
I hope this clears things up for you! And remember, don't get too caught up in the symbols. Just make sure you understand the concepts behind the equations.
I understand that you're having trouble understanding the symbols and equations in the problem. Let me walk you through the correct approach for solving it step by step.
The given balanced chemical equation is:
4Au + 8KCN + O2 + 2H2O -> 4KAu(CN)2 + 4KOH
To find the minimum amount of KCN needed to extract 29.0 g of gold, we need to use stoichiometry.
Step 1: Calculate the molar mass of gold (Au):
The molar mass of gold (Au) is 197.0 g/mol.
Step 2: Convert the given mass of gold to moles:
moles of gold (Au) = mass / molar mass = 29.0 g / 197.0 g/mol = 0.1472 mol
Step 3: Use the stoichiometry of the balanced equation to find the moles of KCN required.
From the balanced equation, we see that the coefficient of KCN is 8, which means that 8 moles of KCN are required to react with 4 moles of gold (Au).
moles of KCN = (0.1472 mol Au) * (8 mol KCN / 4 mol Au) = 0.2944 mol KCN
So, the minimum amount of KCN in moles needed to extract 29.0 g of gold is 0.2944 mol KCN.
I hope this clarifies the correct approach to solving the problem and the symbols used in the equations. Let me know if you have any further questions!
I understand your confusion. Let me explain the correct way to approach this problem and clarify the symbols you should use.
First, let's define the symbols we will use:
- m_Au: mass of gold to be extracted (29.0 g)
- M_Au: molar mass of gold (197.0 g/mol)
- n_KCN: amount in moles of potassium cyanide (KCN) needed
- M_KCN: molar mass of KCN (65.12 g/mol)
- n_Au: amount in moles of gold (to be determined)
The balanced equation given is:
4Au + 8KCN + O2 + 2H2O → 4KAu(CN)2 + 4KOH
Now, let's use the equation you mentioned: mass = (molecular mass)(moles of mass)
For gold (Au):
m_Au = n_Au * M_Au
To solve for n_Au, rearrange the equation:
n_Au = m_Au / M_Au
Here, you have correctly calculated n_Au as:
n_Au = (29.0 g) / (197.0 g/mol) ≈ 0.147 moles
Now, let's focus on the amount of KCN (n_KCN) needed. According to the balanced equation, it is reacting in a 1:2 ratio with gold. So, the moles of KCN (n_KCN) can be calculated using the stoichiometric ratio:
n_KCN = (2/4) * n_Au
= (2/4) * 0.147 moles (since n_Au = 0.147 moles)
= 0.0735 moles
Therefore, the minimum amount of KCN needed to extract 29.0 g of gold is approximately 0.0735 moles.
To summarize the symbols:
- m_Au: mass of gold
- M_Au: molar mass of gold
- n_KCN: amount in moles of potassium cyanide (KCN)
- M_KCN: molar mass of KCN
- n_Au: amount in moles of gold
I hope this clarifies the symbols and helps you understand how to approach this type of problem. Let me know if you have any further questions!