Answer: On heating, Magnesium forms its oxide; while potassium manganate(VII) decomposes
Explanation:
Magnesium Mg, on heating forms Magnesium oxide
2Mg(s) + O2(g) --> 2MgO
Potassium permanganate KMnO4, on heating decomposes to potassium manganate K2MnO4, manganese dioxide MnO2, and Oxygen gas O2.
2KMnO4 --> K2MnO4 + MnO2 + O2
The difference in observation is that, on heating, Magnesium forms its OXIDE as product; while potassium manganate(VII) decomposes, giving OFF most of its constituents and reducing its weight.
The reaction equation is:
Li + Br → LiBr
39 grams of Li = 39 / 7 = 5.57 moles of lithium
41.5 grams of Br = 41.5 / 80 = 0.52 mole of bromine
<u>Answer: </u>
A sample initially contained 150 mg of radon-222. After 11.4 days only 18.75mg of the radon-222 in the sample remained where 3 half-lives have passed
<u>Explanation:</u>
Given, the initial value of the sample,
= 150mg
Final value of the sample or the quantity left, A = 18.75mg
Time = 11.4 days
The amount left after first half life will be ½.
The number of half-life is calculated by the formula

where N is the no. of half life
Substituting the values,


On equating, we get, N = 3
Therefore, 3 half-lives have passed.