When 2.47 g of chromium is reacted with an excess of sulphur, the compound Cr2S3 results. Treating the Cr2S3 so formed with strontium metal converts all of the sulphur to SrS. Reacting the SrS with sodium metal then converts all the SrS to Na2S. What mass in grams of Na2S is produced?
1. First you must write the equations and balance them.
2. Convert 2.47 g Cr to mols remembering that mols = grams/atomic mass.
3. Convert mols Cr to mols Na2S using the coefficients in the balanced equations.
4. Convert mols Na2S to grams using grams = mols x molar mass.
Note: You CAN simply do this as three or four problem and determine the mols Cr2S3 formed, then mols SrS formed, then mols Na2S formed but that is the long way of doing it. Post your work if you get stuck.
To determine the mass of Na2S produced, we need to follow the given reactions and apply stoichiometry to calculate the amount of Na2S formed.
First, let's write out the balanced equations for the reactions:
1) Chromium (Cr) reacts with sulfur (S) to form chromium(III) sulfide (Cr2S3):
4 Cr + 3 S --> 2 Cr2S3
2) Chromium(III) sulfide (Cr2S3) reacts with strontium (Sr) to form strontium sulfide (SrS):
Cr2S3 + 3 Sr --> 2 Cr + 3 SrS
3) Strontium sulfide (SrS) reacts with sodium (Na) to form sodium sulfide (Na2S):
SrS + 2 Na --> Sr + Na2S
Now, let's calculate the amount of Na2S produced step by step:
Step 1: Calculate the number of moles of Cr2S3 formed:
Given mass of Cr = 2.47 g
Molar mass of Cr = 52 g/mol
Moles of Cr = (2.47 g) / (52 g/mol)
From the balanced equation, the mole ratio between Cr and Cr2S3 is 4:2, so:
Moles of Cr2S3 formed = 0.5 * Moles of Cr
Step 2: Calculate the number of moles of SrS formed:
From the balanced equation, the mole ratio between Cr2S3 and SrS is 1:3, so:
Moles of SrS formed = 3 * Moles of Cr2S3 formed
Step 3: Calculate the number of moles of Na2S formed:
From the balanced equation, the mole ratio between SrS and Na2S is 1:1, so:
Moles of Na2S formed = Moles of SrS formed
Step 4: Calculate the mass of Na2S formed:
Molar mass of Na2S = (22.99 g/mol * 2) + 32.06 g/mol = 87.04 g/mol
Mass of Na2S formed = Moles of Na2S formed * Molar mass of Na2S
Now you can plug in the values and solve for the mass of Na2S formed.