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Artyom0805 [142]
2 years ago
6

WHICH ELEMENT HAS ATOMIC NUMBER 78?

Chemistry
1 answer:
inn [45]2 years ago
3 0

Answer:

platinum

Explanation:

it's atomic number is 78

You might be interested in
B. What useful functions do oxidation numbers
disa [49]

Explanation:

b. What useful functions do oxidation numbers  serve?

It is used to show oxidation and reduction (loss and gain of electrons)

b. How many molecules are in 1 mole of  molecules?

1 mole = 6.022 * 10^23 molecules

c. What is the name given to the number of  molecules in 1 mole?

Avogadro's Number of molecules

21. a. What is the molar mass of an element?

This is the mass of an element divided by the number of moles.

Molar mass = Mass / Number of moles

b. Write the molar mass rounded to two  decimal places of carbon, neon, iron and  uranium.

amu = Atomic Mass Unit

Carbon = 12.01 amu

Neon = 20.18 amu

Iron = 55.85 amu

Uranium = 238.03 amu

7 0
3 years ago
6.75 L of carbon dioxide gas are stored at a pressure of 175 atm. If the temperature and number of gas particles do not change,
I am Lyosha [343]

Answer:

4.24 L

Explanation:

  • 6.75 L - 175 atm

x. - 110 atm

  • <u>175atm </u><u>x</u>=<u>742.5L /atm</u>

175atm 175atm

  • therefore x=4.24 L
3 0
3 years ago
How is an atomic mass unit defined?
rusak2 [61]
A unit of mass used to express atomic and molecular weights, equal to one-twelfth of the mass of an atom of carbon-12. It is equal to approximately 1.66 x 10-27<span> kg.</span>
6 0
3 years ago
Determine the root-mean square speed of CO2 molecules that have an average kinetic energy of 4.2 x10-21 J per molecule.
strojnjashka [21]
<span>Determine the root-mean-square sped of CO2 molecules that have an average Kinetic Energy of 4.21x10^-21 J per molecule. Write your answer to 3 sig figs.
</span><span>
E = 1/2 m v^2 

If you substitute into this formula, you will get out the root-mean-square speed. 

If energy is Joules, the mass should be in kg, and the speed will be in m/s. 

1 mol of CO2 is 44.0 g, or 4.40 x 10^1 g or 4.40 x 10^-2 kg. 

If you divide this by Avagadro's constant, you will get the average mass of a CO2 molecule. 

4.40 x 10^-2 kg / 6.02 x 10^23 = 7.31 x 10^-26 kg 

So, if E = 1/2 mv^2 

</span>v^2 = 2E/m = 2 (4.21x10^-21 J)/7.31 x 10^-26 kg = 115184.68 
Take the square root of that, and you get the answer 339 m/s.
8 0
3 years ago
Dr. I. M. A. Brightguy adds 0.1727 g of an unknown gas to a 125-mL flask. If Dr. B finds the pressure to be 736 torr at 20.0°C,
AlladinOne [14]

Answer:

The gas that Dr. Brightguy added was O₂

Explanation:

Ideal Gases Law to solve this:

P . V = n . R . T

Firstly, let's convert 736 Torr in atm

736 Torr is atmospheric pressure = 1 atm

20°C = 273 + 20 = 293 T°K

125 mL = 0.125L

0.125 L . 1 atm = n . 0.082 L.atm / mol.K . 293K

(0.125L .1atm) / (0.082 mol.K /L.atm . 293K) = n

5.20x10⁻³ mol = n

mass / mol = molar mass

0.1727 g / 5.20x10⁻³ mol = 33.2 g/m

This molar mass corresponds nearly to O₂

7 0
3 years ago
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