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3 years ago

After 11.5 days, 12.5% of a sample of radon-222 that originally weighed 42g remains. What is the half-life of this isotope?

1 answer:

5 0

Half-life is defined as the amount of time it takes a given quantity to decrease to half of its initial value. The equation to describe the decay is
Nt=N0(1/2) $^{t/t(1/2)}$ where N0 is the initial quantity, Nt is the remaining quantity after time t, t1/2 is the half-time. So work out the equation, t1/2 = t (-ln2)/ln(Nt/N0) = 11.5*(-ln2)/ln(12.5/100) = 3.83 days

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A chemistry student must write down in her lab notebook the concentration of a solution of sodium hydroxide. The concentration o

taurus [48]

Answer:

The concentration the student should write down in her lab is 2.2 mol/L

Explanation:

Atomic mass of the elements are:

Na: 22.989 u

S: 32.065 u

O: 15.999 u

Molar mass of sodium thiosulfate, Na2S2O3 = (2*22.989 + 2*32.065 + 3*15.999) g/mol = 158.105 g/mol.

Mass of Na2S2O3 taken = (19.440 - 2.2) g = 17.240 g.

For mole(s) of Na2S2O3 = (mass taken)/(molar mass)

= (17.240 g)/(158.105 g/mol) = 0.1090 mole.

Volume of the solution = 50.29 mL = (50.29 mL)*(1 L)/(1000 mL)

= 0.05029 L.

To find the molar concentration of the sodium thiosulfate solution prepared we use the formula:

= (moles of sodium thiosulfate)/(volume of solution in L)

= (0.1090 mole)/(0.05029 L)

= 2.1674 mol/L

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3 years ago

How do the isotopes hydrogen-1 and hydrogen-2 differ?

g100num [7]

<span>Hydrogen-2 has one neutron; hydrogen-1 has none</span>

4 0

3 years ago

Read 2 more answers

How many kilocalories are required to increase the temperature of 15.6 g of iron from 122 °c to 355 °c. the specific heat of iro

Dmitriy789 [7]

Heat require to boil 15.6 g iron from 122 C0to 355 C0 whereas,

$Q = m s dT$

Where, m is mass of iron

s is specific heat of iron

d T is change in temperature in celcius

$= 15.6 g * 0.45 J /g /C * (355 - 122) = 1.63 * 10^3 J$

1 cal = 4.2 J

Then,

$Q = (1.63 * 10^3) /4.2 = 0.389 K cal$

Thus 0.389 k cal of enrgy is required by a 15.6 g Fe to reach to 355 C^0

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3 years ago

Why alkali metals easly ionize

Dmitriy789 [7]

Here’s what I found:

It takes very little energy to remove that outermost electron from an alkali metal. Thus, alkali metals easily lose their outermost electron to become a +1 ion. ... In fact, as you go down the 1A column, the first ionization energies get lower and lower, making cesium the most easily ionized element on the periodic table.

So basically it’s because part of what makes alkali metals so reactive is that they have one electron in their outermost electron layer.

7 0

3 years ago

URGENT: What is different between an ionic bond and a covalent bond?

Fantom [35]

Ionic bond (electrovalent bond) is the exchange of ions between atoms of different element while covalent bond is the sharing electron between atoms

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3 years ago