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lina2011 [118]
1 year ago
12

A new student is planning to use thin layer chromatography (TLC) for his research project. After setting up the apparatus the st

udent forgets to place a lid on the TLC jar. He obtains poor results after running the TLC experiment. Which of the following can best explain his bad results?
A. The open system evaporates the solvent on the TLC plate
B. The open system prevents the evaporation of the solvent in the solution
C. The open system prevents the evaporation of the solvent on the TLC plate
D. The open system evaporates the solvent in the solution
Chemistry
1 answer:
tamaranim1 [39]1 year ago
7 0

Answer:

The open system evaporates the solvent in the solution

Explanation:

An open system is a system in which exchange of materials and energy can occur. If a TLC set up is left open, then the set up constitutes an open system.

During TLC, the sample is dotted on the plate and inserted into a suitable solvent. The solvent moves up the plate and achieves the required separation of the mixture.

Most of these solvents used used TLC are volatile organic compounds. Therefore, if the TLC set up is left open, the solvent will evaporate leading to poor results after running the TLC experiment.

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B5H9(l) is a colorless liquid that will explode when exposed to oxygen. How much heat is released when 0.211 mol of B5H9 reacts
n200080 [17]

Answer:

Heat realesed is - 2192.7 kJ

Explanation:

First lets have the chemical equation balanced, and then solve the question based on the fact that the enthalpy change for a reaction is the sum of the enthalpies of formation of products minus reactants.

    B₅H₉ (l) +     O₂ (g) ⇒       B₂O₃ (s) +      H₂O(l)

B atoms we have 5 reactants and 2 products, so the common mltiple is 10 and we have

  2  B₅H₉ (l) +     O₂ (g) ⇒      5 B₂O₃ (s) +      H₂O(l)

Now balance H  by multiplying by 9 the H₂O

  2  B₅H₉ (l) +     O₂ (g) ⇒      5 B₂O₃ (s) +    9 H₂O(l)

Finally, balance the O since we have 24 in products by multiplying by 12 the

O₂ ,

        2  B₅H₉ (l) +  12 O₂ (g) ⇒      5 B₂O₃ (s) +    9 H₂O

ΔHrxn = 5 x ΔHºf B₂O₃  + 9 x   ΔHºf H₂O  -  ( 2 x ΔHºf  B₅H₉ + 12 x  ΔHºf O₂  )

We have all the  ΔHºf s except oxygen but remember the enthalpy of formation of a pure element in its standard estate is cero.

ΔHrxn =  5 mol x ( -1272 kJ/mol )+ 9 mol  x ( -285.4 kJ/mol )   - (  2mol x 732 kJ/mol )

= -8928.6 kJ - 1464  kJ = -10,392 kJ

Now this enthalpy change was based in 2 mol  reacted according to the balanced equation, so for 0.211 mol of  B₅H₉  we will have:

-10,392 kJ/ 2 mol B₅H₉   x 0.211 mol B₅H₉ = - 2192.7 kJ

8 0
1 year ago
Read 2 more answers
Activity 7: Crossword Puzzle
Ivenika [448]

Answer:

Across

2. Conduction.

3. Plates

4. Convection

5. Subduction

7. Earthquake

Down

1. Radioactive

6. Radiation

8. Sink

9. Slabpull

The clues are;

Across:

2. air molecules come in contact with warmer molecules

3. crust are made up of puzzle - like landmass called_____

4. rising and falling movement of material in the mantle

5. when tectonic plates push with each other

7. it is the result of movement of earth's plate

Down:

1. elements that play a vital role in Earth's internal heat

6. least important mode of heat transport

8. warm material rise; cool material______

9. heats build up underneath the crust

4 0
1 year ago
THESE QUESTIONS ARE ELECTRICIAN REALATED
Vladimir [108]

<span>1.      </span>A.

It is a technique typically engaged in electrical power and electronic devices, wherein the devices are run at less than their rated maximum power degeneracy, taking into account the case or body temperature, the ambient temperature and the type of cooling mechanism used.

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In order to answer the question, you need to know the area of a circle.<span>
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Area = 3.14 * (100/2) ^ 2
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<span>3.      </span>A.

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<span>5.      </span>D.

This is a type of electrical connector used to fasten two or more low-voltage (or extra-low-voltage) electrical conductors.

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<span>7.      </span>D.

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<span>9.      </span>D.

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<span>10.  </span>A.

<span>NEC 310.15(B)(1) and (2), table 310.15(B)(2)(a), and table 310.15(B)(17).
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</span>

<span>11.  </span>A.

<span>12.  </span>B.

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<span>13.  </span>C.

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<span>14.  </span>D.

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<span>15.  </span>A.

<span>16.  </span>D.

<span>17.  </span>C.

Table 310-16 NEC

<span>18.  </span>A <span>
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4 0
2 years ago
Read 2 more answers
Naomi is investigating the properties of a solid material. It takes 120 joules to raise the temperature of 10 grams of the mater
MrRissso [65]
When heat energy is supplied to a material it can raise the temperature of mass of the material.
Specific heat is the amount of energy required by 1 g of material to raise the temperature by 1 °C.
equation is 
H = mcΔt
H - heat energy 
m - mass of material 
c - specific heat of the material 
Δt - change in temperature
substituting the values in the equation 
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c = 2.4 Jg⁻¹°C⁻¹
3 0
2 years ago
A balance measures mass to 0.001 g. If you determine the mass of an object that weighs about 30 g, would you record the mass as
solong [7]

Answer:

The mass is recorded as 32.075 g

Explanation:

"The first digit of uncertainty is taken as the last significant digit", this is the rule for significant figures in the analysis. The balance measures the mass up to three decimal places, so it makes the most sense to note the  whole figure.

8 0
2 years ago
Read 2 more answers
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