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sergij07 [2.7K]

2 years ago

11

A sample of a radioactive isotope initially contains 20 x 10^10 atoms. After 16 days, 5 x 10^10 atoms remain. what is the half-l

ife of the isotope?
A)12 days
B)20 days
C)10 days
D)16 days
E)8 days

1 answer:

nekit [7.7K]2 years ago

7 0

I think the answer is A but I could be wrong

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Nickel can be plated from aqueous solution according to the following half reaction. How long would it take (in min) to plate 29

andrey2020 [161]

Answer:

It take 3.5 *10² min

Explanation:

Step 1: Data given

Mass of the nickel = 29.6 grams

4.7A

Step 2: The balanced equation

Ni2+ (aq- +2e- → Ni(s)

Step 3: Calculate time

W = (ItA)/(n*F)

⇒ W = weight of plated metal in grams = 29.6

⇒ I = current in coulombs per second. = 4.7

⇒ t = time in seconds.

⇒ A = atomic weight of the metal in grams per mole. = 58.69

⇒ n = valence of dissolved metal in solution in equivalents per mole. = 2

⇒ F = Faraday's constant in coulombs per equivalent. F = 96,485.309 coulombs/equivalent.

29.6 = (4.7 * t * 58.69)/(2*96485309)

t = 20707 seconds

t =345 minutes = 3.5 * 10² min

It take 3.5 *10² min

7 0

2 years ago

A solution is made by dissolving 58.125 g of sample of an unknown, nonelectrolyte compound in water. The mass of the solution is

e-lub [12.9K]

Answer:

molecular weight (Mb) = 0.42 g/mol

Explanation:

mass sample (solute) (wb) = 58.125 g

mass sln = 750.0 g = mass solute + mass solvent

∴ solute (b) unknown nonelectrolyte compound

∴ solvent (a): water

⇒ mb = mol solute/Kg solvent (nb/wa)

boiling point:

ΔT = K*mb = 100.220°C ≅ 373.22 K

∴ K water = 1.86 K.Kg/mol

⇒ Mb = ? (molecular weight) (wb/nb)

⇒ mb = ΔT / K

⇒ mb = (373.22 K) / (1.86 K.Kg/mol)

⇒ mb = 200.656 mol/Kg

∴ mass solvent = 750.0 g - 58.125 g = 691.875 g = 0.692 Kg

moles solute:

⇒ nb = (200.656 mol/Kg)*(0.692 Kg) = 138.83 mol solute

molecular weight:

⇒ Mb = (58.125 g)/(138.83 mol) = 0.42 g/mol

8 0

2 years ago

Trichloromethane consists of 10.05% carbon. 0.83% hydrogen and 89.12% chlorine. if uts relative molecular mass is 119.5g . find

Delicious77 [7]

Answer:

C24H2CL213

Explanation:

C

(10.05/100)x119.5

=12x2=24

H

(0.083/100)x119.5

=1x2=2

Cl

(89.12/100)x119.5

=106.5x2=213

4 0

2 years ago

A 1.87 L aqueous solution of KOH contains 155 g of KOH . The solution has a density of 1.29 g/mL . Calculate the molarity ( M ),

lbvjy [14]

Answer:

[KOH] = 1.47 M

[KOH] = 1.22 m

KOH = 6.86 % m/m

Explanation:

Let's analyse the data

1.87 L is the volume of solution

Density is 1.29 g/mL → Solution density

155 g of KOH → Mass of solute

Moles of solute is (mass / molar mass) = 2.76 moles.

Molarity is mol/L → 2.76 mol / 1.87 L = 1.47 M

Let's determine, the mass of solvent.

Molality is mol of solute / 1kg of solvent

We can use density to find out the mass of solution

Mass of solution - Mass of solute = Mass of solvent

Density = Mass / volume

1.29 g/mL = Mass / 1870 mL

Notice, we had to convert L to mL, cause the units of density.

1.29 g/mL . 1870 mL = Mass → 2412.3 g

2412.3 g - 155 g = 2257.3 g of solvent

Let's convert the mass of solvent to kg

2257.3 g / 1000 = 2.25kg

2.76 mol / 2.25kg = 1.22 m (molality)

% percent by mass = mass of solute in 100g of solution.

(155 g / 2257.3 g) . 100g = 6.86 % m/m

5 0

2 years ago

Give four different chemical meanings for the word element and an example of each

Naddika [18.5K]

Answer ;

-An element is a substance containing only one type of atom, for example; H2 or 02 (consisting of atoms that all have the same number of protons).

-Microscopic, single atom of that element

-Macroscopic, sample of that element large enough to weigh on a balance

- A substance that cannot be broken down chemically; e.g; sodium metal,

Explanation;

-An element is a substance whose atoms all have the same number of protons: another way of saying this is that all of a particular element's atoms have the same atomic number. Elements are chemically the simplest substances and hence cannot be broken down using chemical reactions.

-An element is uniquely determined by the number of protons in the nuclei of its atoms.

3 0

2 years ago