washing soda is a hydrate of sodium carbonate. a 2.714 g sample of washing soda is heated until a constant mass of 1.006 of na2co3 is reached. what is the mass of the water evaporated? what is the percent water in the compound?
Na2CO3.xH2O ==> Na2CO3 + xH2O
2.714g.........1.006g.....xg
Now how do you think you can find x g H2O?
Then where do you go for the empirical formula.
To find the mass of water evaporated and the percent water in the compound, we first need to determine the initial mass of water in the hydrate.
1. Calculate the molar mass of sodium carbonate (Na2CO3):
- The atomic mass of sodium (Na) is 22.99 g/mol.
- The atomic mass of carbon (C) is 12.01 g/mol.
- The atomic mass of oxygen (O) is 16.00 g/mol.
- The molar mass of Na2CO3 is 2(22.99) + 12.01 + 3(16.00) = 105.99 g/mol.
2. Determine the number of moles of Na2CO3 in the 2.714 g sample:
- The molar mass of Na2CO3 is 105.99 g/mol.
- The number of moles of Na2CO3 = mass / molar mass = 2.714 g / 105.99 g/mol = 0.025 g/mol.
3. Since washing soda is a hydrate, it contains water molecules. NA2CO3.xH2O represents the formula of washing soda, where "x" represents the number of water molecules per mole of Na2CO3.
4. Calculate the molar mass of the water:
- The molar mass of H2O (water) is 18.02 g/mol.
5. Determine the number of moles of H2O in the 0.025 g of Na2CO3:
- From the balanced chemical formula, we know that for each mole of Na2CO3 (molar mass 105.99 g/mol), there are x moles of H2O (molar mass 18.02 g/mol).
- We can set up a ratio: x moles H2O / 0.025 moles Na2CO3 = 18.02 g/mol / 105.99 g/mol.
- Solving for x: x = (0.025 moles Na2CO3) * (18.02 g/mol / 105.99 g/mol) = 0.0043 moles H2O.
6. Calculate the mass of water evaporated:
- The mass of water evaporated is given by: mass = moles x molar mass = 0.0043 moles H2O x 18.02 g/mol = 0.0778 g.
7. Calculate the percent water in the compound:
- The percent water is given by: (mass of water evaporated / initial mass of the washing soda sample) x 100.
- Using the values we obtained: (0.0778 g / 2.714 g) x 100 = 2.87%.
So, the mass of water evaporated is 0.0778 g, and the compound is 2.87% water by mass.