Pure platinum is too soft to be used in jewelry because it scratches easily. To increase the hardness so that it can be used in jewelry, platinum is combined with other metals to form an alloy. To determine the amount of platinum in an alloy, a 7.804 g sample of an alloy containing platinum and cobalt is reacted with excess nitric acid to form 2.03 g of cobalt (II) nitrate. Calculate the mass percent of platinum in the alloy.
Please help!!
find the moles of cobalt nitrate ... divide 2.03 g by the molar mass (182.9 g)
... this is also the moles of cobalt
find the mass of cobalt ... multiply the moles by the molar mass (58.93 g)
find % of cobalt in alloy ... divide mass of cobalt by mass of alloy
mass % of platinum is ... 100% minus % of cobalt
There is nothing particularly wrong with what you wrote but you don't need all of that work. You already have the mass Co. Your step 1 converts g Co to mols and step 2 converts back to grams so you're back to where you started. Then you find %Co, which the problem doesn't ask for and subtract from 100 to find %Pt. Why not find % Pt directly?
Hi,
So I calculated 7.804g - 2.03g which equals to 5.774g. (Is that what you meant by a better answer?) Would it be correct if I used that (5.774g) and divide by the total mass (7.804g) so that it would become ~0.7399? And the answer would be 73.99%? I'm just unsure because in the question, it says cobalt nitrate, not just cobalt. Sorry if this is confusing.
To calculate the mass percent of platinum in the alloy, we need to determine the amount of platinum and cobalt in the given sample.
Let's start by getting the amount of cobalt (II) nitrate produced from the reaction. We know that the reaction is between cobalt and nitric acid, which results in cobalt (II) nitrate. The balanced equation for the reaction is:
Co + 2HNO3 → Co(NO3)2 + H2O
From the equation, we can see that one mole of cobalt (Co) reacts to form one mole of cobalt (II) nitrate (Co(NO3)2). We can use the molar mass of cobalt (II) nitrate (Co(NO3)2) to convert the given mass of cobalt (II) nitrate (2.03 g) to moles.
The molar mass of cobalt (II) nitrate (Co(NO3)2) is calculated as follows:
Cobalt (Co) has a molar mass of 58.93 g/mol.
Nitrogen (N) has a molar mass of 14.01 g/mol, and there are two nitrogen atoms in cobalt (II) nitrate.
Oxygen (O) has a molar mass of 16.00 g/mol, and there are six oxygen atoms in cobalt (II) nitrate.
Molar mass of cobalt (II) nitrate (Co(NO3)2) = (58.93 g/mol) + 2[(14.01 g/mol) + 3(16.00 g/mol)]
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 58.93 g/mol + 2(14.01 g/mol + 48.00 g/mol)
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 58.93 g/mol + 2(14.01 g/mol + 48.00 g/mol)
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 58.93 g/mol + 2(14.01 g/mol + 48.00 g/mol)
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 58.93 g/mol + 2(62.01 g/mol)
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 58.93 g/mol + 124.02 g/mol
Molar mass of cobalt (II) nitrate (Co(NO3)2) = 182.95 g/mol
Now, we can convert the mass of cobalt (II) nitrate (2.03 g) to moles using its molar mass:
Moles of cobalt (II) nitrate = mass / molar mass
Moles of cobalt (II) nitrate = 2.03 g / 182.95 g/mol
Next, we need to determine the ratio of platinum to cobalt in the alloy. Since the reaction resulted in the production of cobalt (II) nitrate, we can infer that the cobalt came from the alloy. Therefore, the number of moles of cobalt (II) nitrate is equal to the number of moles of cobalt in the alloy.
Now, we can calculate the moles of cobalt in the alloy.
Moles of cobalt in the alloy = moles of cobalt (II) nitrate
Next, we need to find the moles of platinum in the alloy. Since the platinum is combined with cobalt to form an alloy, we can subtract the moles of cobalt from the total moles of the alloy to get the moles of platinum.
Moles of platinum in the alloy = total moles of alloy - moles of cobalt in the alloy
Finally, we can find the mass percent of platinum in the alloy.
Mass percent of platinum in the alloy = (mass of platinum / mass of alloy) × 100
Substituting in the values we've calculated, we can solve the equation to get the mass percent of platinum in the alloy.
Please provide the mass of the alloy so that we can proceed with the calculation.
7.804 g = mass Co + Pt
-2.03 g = mass Co
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about 5.8 g = mass Pt but you need a better answer
%Pt = (mass Pt/mass sample)*100 = ?