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Elden [556K]
3 years ago
6

How many milligrams of a 20mg sample of cesium-137 remain after 60 years

Chemistry
1 answer:
andrey2020 [161]3 years ago
5 0
Cs -137 has a half life of about 30 years. If 60 years pass, there is two half lives passed so 1/2 * 1/2= 1/4. Take 1/4 and multiply it with the mass given:
(1/4)*20mg=5mg left
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A radio wave travels 186,000 miles per second. How many kilometers will the wave travel in one microsecond? (1 mile = 1.61 km)
Komok [63]
1) 1 second = 1000000 microseconds

2) 186000 / 1.61 = 115527.9503 Km

3) We use the equation:
Speed = distance / time

4) rearrange for distance by multiplying both sides by time to get;

Distance = speed x time


5) plug in the values:

Distance = 115527.9503 x 0.000001
= 0.1155279503 Km
6 0
3 years ago
Liquid nitrogen is cold and can be used to cool objects to -196°C. If you put the bottle of warm air in liquid nitrogen at this
shtirl [24]

Answer:

It will boil.

Literally, every liquid has a boiling point, unless it chemically decomposes before it gets to that point (which liquid nitrogen certainly doesn't). At normal atmospheric pressure, it can be 'heated' to -196 C. At that point, any heat you put into it will go into boiling liquid nitrogen into nitrogen gas. At higher pressures, the same thing will happen at a higher temperature. Once all the liquid is boiled, the gas will continue to rise in temperature as long as heat is being added.

Explanation:

8 0
2 years ago
A student is performing a titration to determine the concentration of a 20.0 mL sample of hydrochloric acid. What did the studen
irakobra [83]

Answer:

0.25M HCl

Explanation:

The reaction of HCl with NaOH is:

HCl + NaOH ⇄ H₂O + NaCl

<em>Where 1 mole of HCl reacts per mole of NaOH</em>

The end point was reached when the student added:

0.0500L × (0.1mol / L) = 0.00500 moles of NaOH

As 1 mole of HCl reacted per mole of NaOH, moles of HCl present are:

<em>0.00500 moles HCl</em>

The volume of the sample of hydrochloric acid was 20.0mL = 0.0200L, and concentration of the sample is:

0.00500 mol HCl / 0.0200L = <em>0.25M HCl</em>

8 0
3 years ago
T/F according to the law of conservation of energy, when you use energy
Bond [772]
I think the answer is false
5 0
3 years ago
An aqueous solution of 1.29 M ethanol, CH3CH2OH, has a density of 0.988 g/mL. The percent by mass of CH3CH2OH in the solution is
anzhelika [568]

Answer:

6%

Explanation:

Hello, for this case, we assume that the volume of the solution is 1L, thus, the mass is given by using the density as follows:

m_{solution}=1L*\frac{1000 mL}{1L}*\frac{0.988g}{1mL} =988g

Now, the mass of the ethanol:

m_{C_2H_5OH}=(1.29molC_2H_5OH/L*1L)*\frac{46gC_2H_5OH}{1molC_2H_5OH} \\m_{C_2H_5OH}=59.34g

Finally, the by mass percent is:

m/m=\frac{59.34g}{988g}*100\\%

%m=6%

Best regards.

4 0
3 years ago
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