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Brilliant_brown [7]
3 years ago
12

The starting amount of radioactive iodine-131 was 250 g. The half-life is 8 days. When Leslie measured the amount, she measured

15.625 g of radioactive iodine. How many days have elapsed between measurements
Chemistry
1 answer:
love history [14]3 years ago
3 0

Answer:

32 days

Explanation:

Half life is the amount of time it takes to get to half of the starting concentration / amount.

Starting amount = 250 g

Half life = 8 days

Amount left = 15.625 g

How many days ? That is, how many half lives....

After first Half life;

Amount left = 250 / 2 = 125 g

After second half life;

Amount left = 125 / 2 = 62.5 g

After third half life;

Amount left = 62.5 / 2 = 31.25 g

After fourth half life;

Amount left = 31.25 g / 2 = 15.625 g

That is the radioactive iodine - 131 went though four half lives.

How many days = Number of half lives * Half life

How many days = 4 * 8 = 32 days

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Vikentia [17]

Answer:

A compressed spring

Explanation:

A compressed spring has potential energy only and no kinetic energy.

This is because kinetic energy is only possessed by particles in motion.

Energy in a compressed spring= -1/2kx² where x is the displacement.

In this equation there is no velocity so there is no kinetic energy.

3 0
3 years ago
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How many milliliters of 0.1 m hcl is required to react with 0.15g sodium carbonate (na2co3?
docker41 [41]
1) Write the balanced chemical equation

     2HCl + Na2 CO3 ----------> 2NaCl + H2CO3

2) Write the molar ratios:

    2 mol HCl : 1 mol Na2CO3 : 2 mol NaCl : 1 mol H2CO3

3) Convert 0.15g of sodium carbonate to number of moles

3a) Calculate the molar mass of Na2CO3

Na: 2 * 23 g/mol = 46 g/mol

C: 12 g/mol =

O: 3 * 16 g/mol = 48 g/mol

molar mass = 46g/mol + 12g/mol + 48g/mol = 106 g/mol

3b.- Calculate the number of moles of Na2CO3

# moles = grams / molar mass = 0.15 g / 106 g/mol = 0.0014 mol Na2CO3

4) Calculate the number of moles of HCl from the molar proportion:

[0.0014 mol Na2CO3] * [2 mol HCl / 1 mol Na2CO3] = 0.0028 mol HCl

5) Calculate the volume of HCl from the definition of Molarity

Molarity, M = # moles / volume in liters

=> Volume in liters = # moles / M = 0.0028 mol / 0.1 M = 0.028 liters

0.028 liters * 1000 ml / liter = 28 ml.

Answer: 28 mililiters of 0.1 M HCl.
7 0
3 years ago
The following two compounds are constitutional isomers. Identify which of these is expected to be more acidic, and explain your
Vladimir [108]

Answer:

c. Compound 2 is more acidic because its conjugate base is more resonance stabilized

Explanation:

You haven't told us what the compounds are, so let's assume that the formula of Compound 1 is HCOCH₂OH and that of Compound 2 is CH₃COOH.

The conjugate base of 2 is CH₃COO⁻. It has two important resonance contributors, and the negative charge is evenly distributed between the two oxygen atoms.

CH₃COOH + H₂O ⇌ CH₃COO⁻ + H₃O⁺

The stabilization of the conjugate base pulls the position of equilibrium to the right, so the compound is more acidic than 1.

6 0
3 years ago
Given the following data:N2(g) + O2(g)→ 2NO(g), ΔH=+180.7kJ2NO(g) + O2(g)→ 2NO2(g), ΔH=−113.1kJ2N2O(g) → 2N2(g) + O2(g), ΔH=−163
statuscvo [17]

Answer:

ΔH = +155.6 kJ

Explanation:

The Hess' Law states that the enthalpy of the overall reaction is the sum of the enthalpy of the step reactions. To do the addition of the reaction, we first must reorganize them, to disappear with the intermediaries (substances that are not presented in the overall reaction).

If the reaction is inverted, the signal of the enthalpy changes, and if its multiplied by a constant, the enthalpy must be multiplied by the same constant. Thus:

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The intermediares are N₂ and O₂, thus, reorganizing the reactions:

N₂(g) + O₂(g) → 2NO(g) ΔH = +180.7 kJ

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N₂O(g) → N₂(g) + (1/2)O₂(g) ΔH = -81.6 kJ (multiplied by 1/2)

------------------------------------------------------------------------------------

N₂O(g) + NO₂(g) → 3NO(g)

ΔH = +180.7 + 56.55 - 81.6

ΔH = +155.6 kJ

5 0
3 years ago
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