A 0.9000g sample of a mixture NaCl and KCl is dissolved in water and the solution is then treated with an excess of AgNO3 to yield 1.933g of AgCl. Calculate the percent by mass of each compound in the mixture
Ag = 108 g/mol
Cl = 35.5 g/mol
AgCl = 108 + 35.5 = 143.5 g/mol
1.933/143.5 = .0135 mols of AgCl so used .0135 mols of Cl
.0135 * 35.5 = .478 grams of Cl used
Na = 23 g/mol so NaCl = 58.5 g/mol
K = 39 g / mol so KCl = 74.5 g/mol
say used x grams NaCl and (.9 - x) grams of KCl
x grams NaCl --> x/58.5 mols NaCl
(.9-x)grams KCl --->(.9-x)/74.5 mols KCl
BUT we know that .0135 mols Cl were used
SO x/23 + (.9-x)/74.5 = .0135
solve for x, the grams of NaCl, .9-x the grams of KCl etc
100 (x/.9) = percent Na
To calculate the percent by mass of each compound in the mixture, we first need to determine the masses of NaCl and KCl in the sample.
1. Calculate the mass of AgCl formed:
Mass of AgCl = 1.933 g
2. Determine the mass of Cl in AgCl:
The molar mass of Cl is 35.45 g/mol.
Number of moles of Cl = Mass of AgCl / Molar mass of Cl
= 1.933 g / 35.45 g/mol
3. Determine the number of moles of NaCl and KCl:
Since AgNO3 reacts with Cl to form AgCl, we know that the moles of Cl come from NaCl and KCl in the mixture. The ratio of moles of Cl to moles of NaCl is 1:1 and to moles of KCl is also 1:1.
4. Calculate the mass of NaCl and KCl:
Mass of NaCl = Moles of NaCl * Molar mass of NaCl
Mass of KCl = Moles of KCl * Molar mass of KCl
5. Calculate the percent by mass of NaCl and KCl:
Percent by mass of NaCl = (Mass of NaCl / Total mass of the mixture) * 100
Percent by mass of KCl = (Mass of KCl / Total mass of the mixture) * 100
By following these steps, you should be able to calculate the percent by mass of each compound in the mixture.