this is for a lab - determining the chemical formula of a hydrate.
suppose the hydrate was heated too quickly and some of it was lost of spattered out of the container.
explain how hthis would effect
a) the calculated percent by mass of water in the compound
b) the molecular formula u determined
THX
a). It's easier to explain with an example. Suppose we start with MgSO4.xH2O and we want to determine x.
Suppose we took a 10.000 g sample of MgSO4.xH2O and it lost 5.116 g on heating. So the water content is 5.116 g and the MgSO4 content is 10.000 - 5.116 = 4.884 g.
Here is what we do.
5.116/18.015 = 0.284 = moles H2O.
4.884/120.37 = 0.0406 = moles MgSO4.
Then 0.284/0.0406 = 7 so the formula is
MgSO4.7H2O.
NOW, if we heated too fast and some of the sample spattered, what happens. When you reweigh the sample too much mass has been lost, so the mass H2O is too high and when you subtract from 10.000, the mass of MgSO4 too low. So the percent H2O is too high (70% using the numbers from b part) and the MgSO4 is too low (30% using the numbers from b part).[Percent MgSO4 should be 48.84% and percent H2O should be 51.16%.]
b) Suppose the loss in spattering is 7.0 g just to make things simple. Then mass H2O = 7 g and 10-7 = 3 g MgSO4.
Now 7/18=0.389
and 3/120 = 0.025, then
0.389/0.025 = 15.6 which we might round to 16 and the formula would be MgSO4.16H2O.
I hope this helps.
When a hydrate is heated too quickly, some of the water molecules may be lost or spattered out of the container. This can have two effects on the determination of the chemical formula of the hydrate:
a) Calculated percent by mass of water in the compound: The percent by mass of water in a hydrate is usually determined by measuring the mass loss of the hydrate upon heating. Heating the hydrate too quickly and causing spattering or loss of water molecules can result in an underestimation of the mass loss. This means that the calculated percent by mass of water in the compound would be lower than the actual value. So, the calculated percent by mass of water in the compound would be lower than what it should be.
b) Molecular formula determination: The loss of water molecules from the hydrate during heating can affect the determination of the molecular formula. The molecular formula of a hydrate represents the ratio between the number of water molecules to the other compound in the hydrate. If some of the water molecules are lost, it would lead to an incorrect ratio and subsequently impact the determination of the molecular formula. The calculated molecular formula would likely be inconsistent with the actual molecular formula of the hydrate.
Therefore, it is important to ensure controlled heating and avoid rapid or excessive heating to prevent the loss or spattering of water molecules during the determination of the chemical formula of a hydrate.
When a hydrate is heated too quickly and some of it is lost or spattered out of the container, it can affect both the calculated percent by mass of water in the compound and the determined molecular formula. Here's how:
a) The calculated percent by mass of water in the compound:
The percent by mass of water in a hydrate is calculated by dividing the mass of water lost during heating by the initial mass of the hydrate and multiplying by 100. When some of the hydrate is lost or spattered out, the initial mass of the hydrate that you start with will be smaller. This will result in an underestimation of the mass of water lost, and therefore an underestimated percent by mass of water in the compound.
b) The molecular formula:
The molecular formula of a hydrate represents the ratio of water molecules to the anhydrous compound. When a hydrate is heated too quickly and some of it is lost or spattered out, the ratio of water to the anhydrous compound may be altered. This means that the determined molecular formula may not accurately reflect the true ratio of water to compound. It's important to note that losing some of the hydrate during heating can lead to an incorrect molecular formula if the loss is significant or if it affects the ratio of water to compound in the remaining substance.
To minimize these effects, it is crucial to carefully control the heating process, ensuring that the hydrate is heated gradually and evenly to prevent it from spattering or losing too much mass.