Answer:
B. pour the reagent into a small beaker before using it
Explanation:
Let's explore all the mentioned practice
A. Leftover reagents should not be discarded in the sink but discarded according to the disposal method present in the safety data sheet (SDS) of the chemical.
B. Reagents should be poured in a clean beaker for use to avoid contamination in the original reagent bottle
C. This is not a good practice, as the plastic pipet tends to contain some impurity in its tip.
D. This is also a bad practice. Firstly, a reagent should be taken according to the need. If there is leftover, it should be discarded as it most probably contains contamination in it
You need to use the formula--> P1V1= P2V2 (Boyles's law)
P1= 14 bar
V1= 312 mL
P2= ?
V2= 652 mL
now we plug the values into the formula.
(14 x 312) = (P2x 652)
P2= (14 x 312)/ 652= <span>6.70 bar</span>
Answer:
6 moles of oxygen are needed to make 12 moles of magnesium oxide.
Explanation:
First of all you should know that the balanced chemical equation is:
2 Mg + O₂ → 2 MgO
The rule of three or is a way of solving problems of proportionality between three known values and an unknown value, establishing a relationship of proportionality between all of them. That is, what is intended with it is to find the fourth term of a proportion knowing the other three. Remember that proportionality is a constant relationship or ratio between different magnitudes.
If the relationship between the magnitudes is direct, that is, when one magnitude increases, so does the other (or when one magnitude decreases, so does the other) , the direct rule of three must be applied. To solve a direct rule of three, the following formula must be followed:
a ⇒ b
c ⇒ x
So:

In this case the rule of three applies as follows: if 2 moles of magnesium oxide are produced from 1 mole of oxygen, 12 moles of magnesium oxide from how many moles of oxygen is produced?

moles of oxygen= 6
<u><em>6 moles of oxygen are needed to make 12 moles of magnesium oxide.</em></u>