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MA_775_DIABLO [31]
3 years ago
12

A worker is exposed to the following airborne concentrations of ethylbenzene: 8:00 – 10:00 125 ppm 10:15 – 12:15 88 ppm 12:45 –

3:15 112 ppm 3:30 – 5:00 70 ppm What is the 8-hour TWA exposure for the employee (calculate the exposure)? Does it exceed the OSHA PEL?
Chemistry
1 answer:
postnew [5]3 years ago
8 0

Answer:

The 8-hour TWA exposure for the employee is 101 ppm and it exceeds the OSHA PEL of 100 ppm for ethylbenzene.

Explanation:

The TWA for 8 hours is calculated by the sum of airbone concentrations multiplied by the time it has been exposed to that period. The total is divided by 8 which refers to the 8 hours total the employee has been exposed.

TWA = (125x2+88x2+112x2.5+70x1.5)/8.

The OSHA PEL is a known number for every compound and it can be find in PEL tables. In the case of ethylbenezene, it is 100 ppm.

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Molten gallium reacts with arsenic to form the semiconductor, gallium arsenide, GaAs, used in light-emitting diodes and solar ce
Vsevolod [243]

Answer:

a) 1.2g of arsenic b) 0.64g of arsenic c) 3.481g of gallium d) 3.806g of gallium e) 2.61g arsenic

Explanation:

The balanced equation is:

Ga + As = GaAs, 1:1 mole ratio

a) mass (gallium)/ molar mass of Ga = 4/ 69.723 = 0.0574mol

Mass (arsenic)/ molar mass of As = 5.5/74.9216 = 0.0734, subtracting the moles from each other (knowing already that the ratio is 1:1), arsenic is in excess by 1.2g

b) repeating the procedure (changing the values)

It will be 0.0574 to 0.06593

Arsenic is in excess by 0.00854

0.00854* mass of arsenic (such must be done for the first remaining mole) = 0.64g

c) the mole ratio is 0.0574: 0.00747

Gallium is in excess by 0.05

Mass of excess gallium = 0.05* 69.723 = 3.481g

d) using the mass given, the new ratio is

0.128: 0.0734

Gallium is in excess by 0.054mol

Mass of excess gallium = 0.054*69.723 = 3.806g

e) using the mass again, the new ratio is 0.0574: 0.02,

Gallium is in excess by 0.0374*69.723 = 2.61g

7 0
3 years ago
"What is the change of entropy for 3.0 kg of water when the 3.0 kg of water is changed to ice at 0"
Artyom0805 [142]

Q: What is the change of entropy for 3.0 kg of water when the 3.0 kg of water is changed to ice at 0 °C? (Lf = 3.34 x 105 J/kg)

Answer:

-3670.33 J/K

Explanation:

Entropy: This can be defined as the degree of randomness or disorderliness of a substance. The S.I unit of Entropy is J/K.

Mathematically,  change of Entropy can be expressed as,

ΔS = ΔH/T ....................................... Equation 1

Where ΔS = Change of entropy, ΔH = heat change, T = temperature.

ΔH = -(Lf×m).................................... Equation 2

Note: ΔH is negative because heat is lost.

Where Lf = latent heat of ice = 3.34×10⁵ J/kg, m = 3.0 kg, m = mass of water = 3.0 kg

Substitute into equation

ΔH = -(3.34×10⁵×3.0)

ΔH = - 1002000 J.

But T = 0 °C = (0+273) K = 273 K.

Substitute into equation 1

ΔS = -1002000/273

ΔS = -3670.33 J/K

Note: The negative value of ΔS shows that the entropy of water decreases when it is changed to ice at 0 °C

4 0
3 years ago
Explain how to convert a mass of compound A to a mass of compound D in words with no equations using the following reaction 2A +
leonid [27]

Answer:

Explanation:

The given reaction equation is:

                2A + 4B → C + 3D

We know the mass of compound A in the reaction above. We are to find the mass of compound D.

We simply work from the known mass to calculate the mass of the unkown compound D

Using the mole concept, we can find the unknown mass.

Procedures

  • We first find the molar mass of the compound A from the atomic units of the constituent elements.
  • We then use the molar mass of A to calculate its number of moles using the expression below:  

            Number of moles of A = \frac{mass of A}{molar mass of A}

  • Using the known number of moles of A, we can work out the number of moles of D.

           From the balanced equation of the reaction, it is shown that:

         2 moles of compound A was used up to produced 3 moles of D

  Then \frac{3}{2} x number of moles of A would give the number of moles of D

  • Now that we know the number of moles of D, we can find its mass using the expression below:

             Mass of D = number of moles of D x molar mass of D

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