I did a lab where I had to decompose the compund patassium cholorate (KClO3)by heating,I had to weight the test tube then the test tube with the potassium chlorate to get the weight. I then had to heat it for several minutes and letting it cool down before weighing it again. Why must the test tube be cool before you weight it? I know because you can't touch it when it's hot, but I am sure there is another reason as well and I am not sure of it. Thank You
Two reasons.
1. The "cold" test tube and contents won't weigh the same as the "hot" test tube and contents.
2. The hot tube will cause air currents to swirl around the balance or whatever weighing mechanism you are using and that will cause uncertainties in the weight of the tube and contents.
How to find the mass of Oxygen that displaces water from the in the decomposition reaction of potassium chlorate using manganese 4 oxide as a catalyst. Am I to use stoichiometry or the combined gas law equation P1V1/T1=P2V2/T2
Yes, you are correct that not being able to touch the test tube when it's hot is indeed one reason for letting it cool down before weighing it again. However, there is another important reason as well.
When you heat the potassium chlorate, it undergoes a chemical reaction known as decomposition, where it breaks down into potassium chloride (KCl) and oxygen gas (O2). The oxygen gas is released into the air while the potassium chloride remains in the test tube.
During the heating process, the potassium chlorate undergoes a chemical change and may also experience physical changes such as expansion or contraction. These changes can affect the weight of the substance in the test tube.
If you were to weigh the test tube while it's still hot, the substances inside might still be undergoing some changes, such as releasing or absorbing gases. This could lead to inaccurate measurements of the weight because the substances in the test tube may not have fully stabilized.
By allowing the test tube to cool down, you ensure that any ongoing chemical reactions or physical changes have ceased, and the substances inside have reached a stable state. This allows for more accurate measurements of the weight of the potassium chloride and any remaining residue in the test tube.