Table of Contents
- 1 Why should the empty crucible be heated to constant weight before using?
- 2 Why is it necessary to heat and mass the crucible before adding the hydrated salt?
- 3 Why do you need to heat the hydrate sample until a constant mass is obtained?
- 4 Why is it important to heat the empty crucible at the beginning of the lab?
- 5 Why does the mass of a crucible decrease when heated?
- 6 Why are the empty crucible and cover fired to red heat?
- 7 Why is it important to heat the hydrate thoroughly?
- 8 Why is it important to leave the lid partly open when first heating the crucible and lid?
- 9 Why was the crucible heated before beginning the hydrated salt lab?
- 10 Why does the empty Crucible need to be heated?
- 11 How do you prevent a false reading in a crucible?
Why should the empty crucible be heated to constant weight before using?
Firstly, preheating of a crucible before use is important for reducing thermal stress on the crucible. A second reason to preheat a crucible is to ensure accurate measurements. If a crucible is weighed cold, or below room temperature, it is possible that moisture may become trapped in the material of the crucible.
Why is it necessary to heat and mass the crucible before adding the hydrated salt?
A 2.914 g sample of gypsum, a hydrated salt of calcium sulfate (CaSO4) is heated at a temperature greater than 170C in a crucible until a constant mass is reaced. During the cooling of the fired crucible, water vapor condensed on the crucible wall before its mass measurement.
Why did we heat the crucible at the beginning of the experiment before we weighed it the first time?
The crucible and lid are heated at the beginning of the experiment before being weighed so that any moisture in the crucible is burned away. Moisture is heavy, and thus it can change the results of the experiment, as we only want the weight of magnesium and the magnesium oxide.
Why do you need to heat the hydrate sample until a constant mass is obtained?
Heating to constant mass ensures that all of the water of hydration has been driven off and we are massing only the anhydrous salt.
Why is it important to heat the empty crucible at the beginning of the lab?
The empty crucible is heated to remove moisture and ensure that the crucible is completely dry as any water present may affect the reading.
Why is it important to heat to a constant mass?
A hydrated compound loses water of crystallisation when it is heated. As it loses water of crystallisation, it loses mass. When it has lost all of its water of crystallisation it is anhydrous . Heat to constant mass to ensure all of the water of crystallisation is removed.
Why does the mass of a crucible decrease when heated?
If it is hotter the weight will be slightly less, if colder slightly more owing to the production of convection currents which affect the apparent mass.
Why are the empty crucible and cover fired to red heat?
The empty crucible and cover are fired to red heat in order to burn off impurities in the crucible and to establish a constant weight.
Why is it important to heat a constant mass?
Why is it important to heat the hydrate thoroughly?
It is important to heat the hydrate thoroughly. If the heating is not enough, the water molecules will not be evaporated. There will be some water that is left in the anhydrous form of the hydrate. The amount of water lost is calculated by subtracting the mass of anhydrous from the mass of hydrate.
Why is it important to leave the lid partly open when first heating the crucible and lid?
While heating the crucible, you must have the lid partially ajar to allow water to escape. You will want a gentle blue flame. Orange flame produces carbon soot which will coat your crucible and alter the weight. Adjust your Bunsen burner away from the crucible then move it into position.
What does it mean to dry to constant mass?
The term constant mass is used to define when a sample is dry. Constant mass – the state at which a mass does not change more than a given percent, after additional drying for a defined time interval, at a required temperature.
Why was the crucible heated before beginning the hydrated salt lab?
1) Which of the following would best explain why the crucible was heated before beginning the Hydrated Salt lab. Heating removes any solid contaminants that would be in the crucible. Heating removes excess moisture from the crucible. Heating activates the protective coating of the crucible.
Why does the empty Crucible need to be heated?
The empty crucible is heated to remove moisture and ensure that the crucible is completely dry as any water present may affect the reading.
What is the purpose of removing the salt from the Crucible?
To drive off any moisture or any volatile impurities from the surface of the crucible. If you are trying to find the percent hydration of your salt, you want your change in mass to correspond only to the mass change of your salt as its water of hydration is lost.
How do you prevent a false reading in a crucible?
Only by heating and reheating to a consistent weight (recommend 3 consecutive identical results – within experimental accuracy) can you be sure that contamination of the crucible itself will not give false readings. “Why was it important to heat the empty crucible to a constant mass before adding the hydrated salt?”