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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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It takes 486.0 kJ/mol to convert sodium atoms to Na+ ions. Sodium atoms absorb and emit light of wavelengths 589.6 and 590.0 nm.
solmaris [256]
We first calculate the energy contained in one photon of this light using Planck's equation:

E = hc/λ

E = 6.63 x 10⁻³⁴ x 3 x 10⁸ / 590 x 10⁻⁹
E = 3.37 x 10⁻²² kJ/photon

Now, one mole of atoms will excite one mole of photons. This means that 6.02 x 10²³ photons will be excited

(3.37 x 10⁻²² kJ/photon) x (6.02 x 10²³ photons / mol)

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8 0
3 years ago
Select all statements that correctly describe the reactions of benzene. A. Benzene typically undergoes reactions in which the ar
Katarina [22]

Answer:Benzene typically undergoes reactions in which the aromatic ring is preserved.B. Benzene typically reacts with electrophiles where an aromatic proton is substituted by the electrophile

Explanation:

The reactions of benzene are such that the aromatic ring is not destroyed. Addition reactions destroy the aromatic ring hence they aren't typical reactions of benzene. Benzene rings are attacked by electrophiles in which reaction a proton is substituted by the electrophile. Alkenes only undergo addition reaction and not electrophilic substitution reaction.

8 0
3 years ago
cylinder contains 250 g of Helium at 200 K. The external pressure is constant at 1 atm. The temperature of the surroundings is l
brilliants [131]

Answer:

The system gains 126100 J

Explanation:

The heat can be calculated by the equation:

Q = nxCxΔT, where Q is the heat, C is the heat capacity,n is the number of moles and ΔT is the variation of temperature (final - initial). The number of moles is the mass divided by the molar mass, so:

n = 250/4 = 62.5 mol.

The system must be in thermal equilibrium with the surroundings, so if the temperature of the surroundings decreased 97 K, the temperature of the system increased by 97 K, so ΔT = 97 K

Q = 62.5x20.8x97

Q = 126100 J

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The recrystallization solvent ought to have a genuinely low breaking point since it makes it simpler for the solvent to vanish out when the arrangement air drys.The breaking point ought to be bring down the softening purpose of the compound.If the breaking point is bigger than the dissolving purpose of the intensify, the crystals will liquefy and turn out as an oil rather than crystals. This would be difficult to examine.
3 0
4 years ago
Can you make an ionic compound with two positive ions? Explain.​
kow [346]
A proper ionic formula has a cation and an anion in it; an ionic compound is never formed between two cations only or two anions only. The key to writing proper ionic formulas is simple: the total positive charge must balance the total negative charge.
8 0
3 years ago
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