For a 5.0 g sample of CoCl3·9H2O, what weight of water (in grams) will be lost if the sample is heated to constant weight (all water driven off)?
Here is a worked example of a stoichiometry problem. Just follow the steps.
http://www.jiskha.com/science/chemistry/stoichiometry.html
There is an easier way to do it. Calculate the percent water in CoCl3.9H2O, then (%H2O/100)*5.00 g = mass H2O lost.
To determine the weight of water lost from a sample of CoCl3·9H2O, we first need to understand the chemical formula of the compound. CoCl3·9H2O represents cobalt(III) chloride hexahydrate, which means it contains one cobalt atom (Co), three chlorine atoms (Cl), and nine water molecules (9H2O) bound to it.
Now, we know that the molar mass of water (H2O) is approximately 18.015 g/mol. Since there are 9 water molecules in CoCl3·9H2O, the molar mass of water in CoCl3·9H2O is 9 * 18.015 g/mol = 162.135 g/mol.
Next, we calculate the molar mass of CoCl3, which consists of one cobalt atom and three chlorine atoms. The atomic mass of cobalt (Co) is approximately 58.933 g/mol, and the atomic mass of chlorine (Cl) is approximately 35.453 g/mol. Therefore, the molar mass of CoCl3 is 58.933 g/mol + 3 * 35.453 g/mol = 129.292 g/mol.
Now that we have determined the molar masses, we can calculate the mass of water in the 5.0 g sample of CoCl3·9H2O. We can set up a proportion using the molar mass of water:
(Weight of water in sample)/(molar mass of CoCl3·9H2O) = (Weight of sample)/(molar mass of CoCl3·9H2O)
Replacing the values:
(Weight of water in sample)/(162.135 g/mol) = (5.0 g)/(129.292 g/mol)
Now we can solve for the weight of water in the sample:
Weight of water in sample = (5.0 g) * (162.135 g/mol) / (129.292 g/mol)
Calculating this expression, we find the weight of water in the sample is approximately 6.274 g.
Therefore, if the sample is heated to constant weight and all the water is driven off, approximately 6.274 grams of water will be lost.