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3 years ago

In 36 hours the amount of radioactive substance has reduced from 80 mg to 10 mg. What is the half-life of this isotope?

1 answer:

6 0

Half-life refers to the time taken for half of the atoms in a radioactive substance to decay. Therefore in 1 half-life the 80 mg of substance will reduce to 40 mg. In another half-life it will reduce from 40 mg to 20 mg, then in a third half-life from 20 mg to 10 mg. Therefore the half-life is equal to the total time taken to decay from 80 mg to 10 mg divided by 3:
t(1/2) = 36 hours / 3 = 12 hours.

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A weak monoprotic acid is titrated with 0.100 MNaOH. It requires 50.0 mL of the NaOH solution to reach the equivalence point. Af

larisa86 [58]

Explanation:

The given reaction is as follows.

$HA(aq) + NaOH (aq) \rightleftharpoons NaA(aq) + H_{2}O(l)$

Hence, number of moles of NaOH are as follows.

n = $0.05 L \times 0.1 M$

= 0.005 mol

After the addition of 25 ml of base, the pH of a solution is 3.62. Hence, moles of NaOH is 25 ml base are as follows.

n = $0.025 L \times 0.1 M$

= 0.0025 mol

According to ICE table,

$HA(aq) + NaOH (aq) \rightleftharpoons NaA(aq) + H_{2}O(l)$

Initial: 0.005 mol 0.0025 mol 0 0

Change: -0.0025 mol -0.0025 mol +0.0025 mol

Equibm: 0.0025 mol 0 0.0025 mol

Hence, concentrations of HA and NaA are calculated as follows.

[HA] = $\frac{0.0025 mol}{V}$

[NaA] = $\frac{0.0025 mol}{V}$

$[A^{-}] = [NaA] = \frac{0.0025 mol}{V}$

Now, we will calculate the $pK_{a}$ value as follows.

pH = $pK_{a} + log \frac{A^{-}}{HA}$

$pK_{a} = pH - log \frac{[A^{-}]}{[HA]}$

= $3.42 - log \frac{\frac{0.0025 mol}{V}}{\frac{0.0025}{V}}$

= 3.42

Thus, we can conclude that $pK_{a}$ of the weak acid is 3.42.

8 0

3 years ago

I need help wit this can someone pls explain???

Crazy boy [7]

Based on the nature of the sub-atomic particles, the correct answers are:

5. No Charge

6. Negative

7. Neutrons and Protons

8. 35 electrons

9. atomic number is 5

10. atomic mass is 11

11. number of protons is 15

12. number of electrons is 20

13. number of neutrons is 30 (55 -25)

14. mass number is 7

15. number of neutrons is 11 (36 - 25)

<h3>What are the sub-atomic particles?</h3>

The sub-atomic particles are the electrons, protons, and neutrons.

The electron is negatively-charged, the proton is positively-charged, whereas, the neutron is neutral and has no charge.

The number of electrons in a neutral atom is equal to the number of protons.

The sum of protons and neutrons gives the mass number of the atom.

Considering the given questions:

5. What type of charge does a neutron have?

Answer = No Charge

6. What type of charge does an electron have?

Answer = Negative

7. Which two subatomic particles are located in the nucleus of an

Answer = Neutrons and Protons

8. If an atom has 35 protons in the nucleus, how many electrons will it have orbiting the nucleus?

Answer = 35 electrons

9. What is the atomic number of the atom in the diagram above?

Answer = atomic number is 5

10. What is the atomic mass/mass number of the atom in the diagram above?

Answer = atomic mass is 11

11. How many protons are in the nucleus of an atom with an atomic number of 15?

Answer = number of protons is 15

12. How many electrons are in the nucleus of an atom with an atomic number of 20?

Answer = number of electrons is 20

13. How many neutrons are in the nucleus of an atom with an atomic number of 25?

Answer = number of neutrons is 30 (55 -25)

14. What is the mass number of an atom with 3 protons, 4 neutrons, and 3 electrons?

Answer = mass number is 7

15. How many neutrons are in the nucleus of an atom that has an atomic mass of 36 and an atomic number of 25?

Answer = number of neutrons is 11 (36 - 25)

In conclusion, the mass number of an atom is the number of protons and neutrons in the nucleus of the an atom.

Learn more about atomic number and mass number at: brainly.com/question/487717

#SPJ1

7 0

2 years ago

Imagine that instead of balls, you were rolling positively charged ions of the same element).

Ghella [55]

The ion with a +3 charge would be deflected the most by the magnet because it has the strongest positive charge therefore it will be the one being the most repelled. and the ion that would be deflected the least would be the ion with a +1 charge because it has the least amount of charge so the magnet will still repel it but just not as much as it will repel the ion with a +3 charge.

hope that helps

8 0

2 years ago

1 C8H10(l) +21/2O2(g) → 8CO2(g) + 5H2O(g), Hcomb= ? Hf for C8H10(l) = +49.0kJ/mol C8H10(l) Use the balanced combustion reaction

nikklg [1K]

Answer:

$H_{comb}=-4406kJ/mol$

Explanation:

Hello,

In this case, the enthalpy of combustion is understood as the energy released when one mole of fuel, in this case octene, is burned in the presence of oxygen and is computed with the enthalpies of formation of the fuel, carbon dioxide and water as shown below (oxygen is circumvented as it is a pure element):

$H_{comb}=8*\Delta _fH_{CO_2}+5\Delta _fH_{H_2O}-\Delta _fH_{C_8H_{10}}$

Thus, since we already know the enthalpy of combustion of the fuel, for carbon and water we have -393.5 and -241.8 kJ/mol respectively, thereby, the enthalpy of combustion turns out:

$H_{comb}=8*(-393.5kJ/mol)+5(-241.8kJ/mol)-49.0kJ/mol\\\\H_{comb}=-4406kJ/mol$

Best regards.

4 0

3 years ago

Consider these elements: p, ca, si, s, ga. a. write the electron configuration for each element

dimulka [17.4K]

Method:

1) Find the atomic number in a periodic table: the number of electrons equal the atomic number

2) Use Aufbau rule

Element atomic number electron configuration

P 15 1s2 2s2 2p6 3s2 3p3

Ca 20 1s2 2s2 2p6 3s2 3p6 4s2

Si 14 1s2 2s2 2p6 3s2 3p2

S 16 1s2 2s2 2p6 3s2 3p4

Ga 31. 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p

7 0

4 years ago