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koban [17]
3 years ago
9

Define atomic numberand mass number. Which can vary without changing the identity of the element?

Chemistry
1 answer:
Volgvan3 years ago
8 0

Explanation:

Atomic number is defined as the number of an element which represents total number of protons.

When an atom is neutral then it means it contains same number of protons and electrons.

On the other hand, atomic mass is defined as the sum of total number of protons and neutrons present in an atom.

Protons of every element remains fixed because it shows the identity of each element but if we change the number of neutrons then also identity of the atom will remain fixed. This is because changing the number of neutrons will not show any change in number of protons.

For example, ^{2}_{1}H and ^{3}_{1}H are isotopes of hydrogen and they have same number of protons but different number of neutrons.

Thus, we can conclude that number of neutrons can vary without changing the identity of the element.

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A lithium flame has a characteristic red color due to emissions of wavelength 671 nm. What is the mass equivalence of 1 mol of p
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Answer:

1.98x10⁻¹² kg

Explanation:

The <em>energy of a photon</em> is given by:

  • E= hc/λ

h is Planck's constant, 6.626x10⁻³⁴ J·s

c is the speed of light, 3x10⁸ m/s

and λ is the wavelenght, 671 nm (or 6.71x10⁻⁷m)

  • E = 6.626x10⁻³⁴ J·s * 3x10⁸ m/s ÷ 6.71x10⁻⁷m = 2.96x10⁻¹⁹ J

Now we multiply that value by <em>Avogadro's number</em>, to <u>calculate the energy of 1 mol of such protons</u>:

  • 1 mol =  6.023x10²³ photons
  • 2.96x10⁻¹⁹ J *  6.023x10²³ = 1.78x10⁵ J

Finally we <u>calculate the mass equivalence</u> using the equation:

  • E=m*c²
  • m=E/c²
  • m =  1.78x10⁵ J / (3x10⁸ m/s)² = 1.98x10⁻¹² kg

6 0
3 years ago
Ammonium hydroxide is _____.<br> an acid<br> a base<br> a neutral
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5. 16.3 g of NaCl is dissolved in water to make 1.75 L of solution. What is the molarity of this solution? A 0.159 M B 0.278 M C
ira [324]

Answer: The molarity of this solution is 0.159 M.

Explanation:

Given: Mass of solute = 16.3 g

Volume = 1.75 L

Number of moles is defined as the mass of substance divided by its molar mass.

Hence, moles of NaCl (molar mass = 58.44 g/mol) ar calculated as follows.

Moles = \frac{mass}{molar mass}\\= \frac{16.3 g}{58.44 g/mol}\\= 0.278 mol

Molarity is the number of moles of a substance present in a liter of solution.

So, molarity of the given solution is calculated as follows.

Molarity = \frac{no. of moles}{Volume (in L)}\\= \frac{0.278 mol}{1.75}\\= 0.159 M

Thus, we can conclude that the molarity of this solution is 0.159 M.

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