The forensic technician at a crime scene has just prepared a luminol stock solution by adding 16.0 g of luminol into a total vol
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Answer:
0.677 moles
Explanation:
Take the atomic mass of K = 39.1, O =16.0, P = 31.0
no. of moles = mass / molar mass
no. of moles of K3PO4 used = 4.79 / (39.1x3 + 31 + 16x4)
= 0.02256 mol
From the equation, the mole ratio of KOH : K3PO4 = 3 :1,
meaning every 3 moles of KOH used, produces 1 mole of K3PO4.
So, using this ratio, let the no. of moles of KOH required to be y.
y = 0.02256 x3
y = 0.0677 mol
If you don't find exactly 0.677 moles as one of the options, go for the closest one. A very slight error may occur because of taking different significant figures of atomic masses when calculating.
Considering the ideal gas law and the definition of molar mass, the molar mass of the sample of gas is 9.17 .
An ideal gas is a theoretical gas that is considered to be composed of randomly moving point particles that do not interact with each other. Gases in general are ideal when they are at high temperatures and low pressures.
The pressure, P, the temperature, T, and the volume, V, of an ideal gas, are related by a simple formula called the ideal gas law:
P×V = n×R×T
where:
- P is the gas pressure.
- V is the volume that occupies.
- T is its temperature.
- R is the ideal gas constant. The universal constant of ideal gases R has the same value for all gaseous substances.
- n is the number of moles of the gas.
The molar mass of substance is a property defined as its mass per unit quantity of substance, in other words, molar mass is the amount of mass that a substance contains in one mole.
<h3>Molar mass of the sample of gas</h3>In this case you know:
- P= 0.980 arm
- V= 1.20 L
- T= 287 K
- R= 0.082
- n= ?
Replacing in the ideal gas law:
0.980 atm× 1.20 L= n× 0.082× 287 K
Solving:
(0.980 atm× 1.20 L)÷ (0.082× 287 K)= n
<u><em>0.04997 moles= n</em></u>
On the other hand, you know that the<u><em> mass of the sample of gas</em></u> is <u><em>0.458 grams</em></u>. Replacing in the definition of molar mass:
Solving:
<u><em>molar mass= 9.17 </em></u>
Finally, the molar mass of the sample of gas is 9.17 .
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