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zhannawk [14.2K]
3 years ago
11

A student determined that the weight-percent recovery for his isolated caffeine proved to be 1.5%. The student was concerned, ex

pecting a yield of at least 50% as in many of the previous experiments. Was his concern legitimate? Explain.
Chemistry
1 answer:
Salsk061 [2.6K]3 years ago
6 0

Yes. Percent yield shows how efficient one's method is. If his isolated caffeine proved to be at only 1.5%, compared to least 50% as in many of the previous experiments, the student should be very concerned as it shows that something caused the yield to sharply drop.

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What is the ph of a solution that has a poh of 11.24
galina1969 [7]
Always remember that pH + pOH = 14 
Here, you have a pOH of 11.24, so  you replace it in the equation, and u get:
pH + 11.24 = 14

Then, You move 11.24 to the other part. and moving from a part to another change the sign of the equation. And you get:
pH = 14 - 11.24 = 2.76

So, the pH of a solution that has a pOH of 11.24 is pH = 2.76

Hope this Helps :)
7 0
3 years ago
How long does it take for a 12.62g sample of ammonia to heat from 209K to 367K if heated at a constant rate of 6.0kj/min? The me
Georgia [21]
First, consider the steps to heat the sample from 209 K to 367K.

1) Heating in liquid state from 209 K to 239.82 K

2) Vaporaizing at 239.82 K

3) Heating in gaseous state from 239.82 K to 367 K.


Second, calculate the amount of heat required for each step.

1) Liquid heating

Ammonia = NH3 => molar mass = 14.0 g/mol + 3*1g/mol = 17g/mol

=> number of moles = 12.62 g / 17 g/mol = 0.742 mol

Heat1 = #moles * heat capacity * ΔT

Heat1 = 0.742 mol * 80.8 J/mol*K * (239.82K - 209K) = 1,847.77 J

2) Vaporization

Heat2 = # moles * H vap

Heat2 = 0.742 mol * 23.33 kJ/mol = 17.31 kJ = 17310 J

3) Vapor heating

Heat3 = #moles * heat capacity * ΔT

Heat3 = 0.742 mol * 35.06 J / (mol*K) * (367K - 239.82K) = 3,308.53 J

Third, add up the heats for every steps:

Total heat = 1,847.77 J + 17,310 J + 3,308.53 J = 22,466.3 J

Fourth, divide the total heat by the heat rate:

Time = 22,466.3 J / (6000.0 J/min) = 3.7 min

Answer: 3.7 min


3 0
3 years ago
6. dissolving ice tea mix in water
Cloud [144]

Answer:

Dissolving ice tea mix in water is a chemical change

Explanation:

It is a chemical change because you can not bring back the ice tea mix back if you mix it in water.

Hope it helps

6 0
3 years ago
Rank the compounds in each set in order of increasing acid strength.
Viktor [21]

Answer:

See explanation

Explanation:

For this question, we have to remember the effect of an atom with high <u>electronegativity</u> as "Br". If the "Br" atom is closer to the carboxylic acid group (COOH) we will have an <u>inductive effect</u>. Due to the electronegativity of Br, the electrons of the C-H bond would be to the Br, then this bond would be <u>weaker</u> and the compound will be more acid (because is easier to produce the hydronium ion H^+).

With this in mind, for A in the last compound, we have <u>2 Br atoms</u> near to the acid carboxylic group, so, we will have a high inductive effect, then the C-H would be weaker and we will have <u>more acidity</u>. Then we will have the compound with only 1 Br atom and finally, the last compound would be the one without Br atoms.

In B, the difference between the molecules is the <u>position</u> of the "Br" atom in the molecule. If the Br atom is closer to the acid group we will have a <u>higher inductive effect</u> and more <u>acidity</u>.

See figure 1

I hope it helps!

5 0
4 years ago
What is the correct scientific notation for 640,000,000? Question 5 options: 6.4X10^8 6.4X10^10 64X10^10 640X10^8
N76 [4]
For very large numbers, it is much more convenient to use scientific notation. To do this, detect first the position of the decimal point. For whole numbers, the decimal point is place implicitly after the very last digit. Then, move this decimal point to the left until you reach to the last digit. In this case, you moved 8 places until you reach 6.4. Because the number is more than 1, the exponent would have a positive sign. Hence, the scientific notation would be 6.4×10⁸.
5 0
4 years ago
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