An anhydrate is the molecule after it has been removed from the water molecule.
The test tube must be cooled before finding its mass because a hot substance has a lower density than a cool substance, therefore, when the formula is used, M=DV, the hotter substance will have a lower mass, and the cool substance will have a higher mass. In addition, a hot test tube could damage the scale, as it is electronic.
The mass of the anhydrous salt must be measured immediately on cooling because the anhydrous salt will want to immediately want to start to bond with water molecules again. The quicker it is measured, the less water molecules it has already begun to bond to.
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The molar mass of zinc is 65.39 g/mol. The molar mass of sulfur is 32.07 g/mol. And the molar mass of oxygen is 16.00 g/mol, but there are four of them, so multiply 16.00 by 4 to get 64.00 g/mol. Then, water has a molar mass of 18.02 g/mol, multiplied by seven because of the coefficient results in 126.14 g/mol. Then, add them all up: 65.39 + 32.07 + 64.00 + 126.14 = 287.60 g/mol ZnSO4・7H2O.
To find the molar mass of the anhydrous salt zinc sulfate, follow the same steps as in #6 minus the seven water molecules. So, the formula would be ZnSO4. Zinc has a molar mass of 65.39 g/mol. Sulfur is 32.07 g/mol. And finally oxygen is 16.00 g/mol times four because there are four of them equals 64.00 g/mol. Then, add them all up, and it results in 65.39 + 32.07 + 64.00 = 161.46 g/mol ZnSO4.
To calculate the percent water in ZnSO4・7H2O, the molar mass of the seven H2O divided by the molar mass of the whole thing, times 100%. First, the molar mass of 7H2O seven (because of the coefficient) times the molar mass of water which is 18.02 g/mol. This results in 126.14 g/mol. Then, the molar mass of the whole thing is 287.60 g/mol, as calculated in #6. SO, divide 126.14 by 287.60 and then multiply by 100% to get that the percent water in ZnSO4・7H2O is 43.8595%, but in significant figures, it is