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Ivahew [28]
3 years ago
10

An element has atomic number 10 and an atomic mass of 20. How many neutrons are in the atom of this element? A. 10 B. 20 C. 30 D

. 0 E. 200
Chemistry
1 answer:
MariettaO [177]3 years ago
3 0

Answer : The correct option is, (A) 10

Explanation :

Atomic number : It is defined as the number of protons or number of electrons.  That means,

Atomic number = number of protons = number of electrons

Atomic mass : It is defined as the sum of number of protons and number of neutrons.

Atomic mass = Number of neutrons + Number of protons

As we are given that,

The atomic number of an element = 10

The atomic mass of an element = 20

Now we have to determine the number of neutrons.

Atomic number = number of protons = 10

Atomic mass = Number of neutrons + Number of protons

Number of neutrons = Atomic mass - Number of protons

Number of neutrons = 20 - 10 = 10

Therefore, the number of neutrons are, 10

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1g Hydrogen

Explanation:

<h3><u>Getting</u><u> </u><u>to</u><u> </u><u>the</u><u> </u><u>equation</u><u>:</u></h3>

Calcium in water reacts vigorously to give a cloudy white <em>Precipitate</em><em> </em>(compound) called Calcium hydroxide alongwith the evolution of Hydrogen gas.

\boxed{ \mathsf{Ca + H_2O \rightarrow Ca(OH)_2 + H_2}}

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

<h3><u>Balancing</u><u> </u><u>the</u><u> </u><u>equation</u><u>:</u><u> </u></h3>

This reaction is not in it's balanced form! The number of atoms of Hydrogen on the left is 2 while that on the right is 4,I.e.,they're not equal.

Adding a 2 in front of H2O solves the problem by making the number of atoms of each element on both the sides equal.

\mathsf{Ca +2 H_2O \rightarrow Ca(OH)_2 + H_2}

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

<h3><u>Observations</u><u>:</u></h3>

Looking into the equation more carefully, we see:

<u><em>1</em><em> </em></u><em>atom</em><em> </em><em>of</em><em> </em><em>Calcium</em><em> </em><em>reacts</em><em> </em><em>with</em><em> </em><em><u>2</u></em><em> </em><em>molecules</em><em> </em><em>of</em><em> </em><em>water</em><em> </em><em>to</em><em> </em><em>give</em><em> </em><u><em>1</em><em> </em></u><em>molecule</em><em> </em><em>of</em><em> </em><em>Calcium</em><em> </em><em>Hydroxide</em><em> </em><em>alongwith</em><em> </em><em><u>1</u></em><em> </em><em>molecule</em><em> </em><em>of</em><em> </em><em>Hydrogen</em><em> </em><em>gas</em><em>.</em>

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

<h3><u>Gram</u><u> </u><u>atomic</u><u> </u><u>and</u><u> </u><u>molecular</u><u> </u><u>masses</u><u> </u></h3>

<u>Mass</u><u> </u><u>of</u><u> </u><u>one</u><u> </u><u>atom</u><u> </u><u>of</u><u> </u><u>Calcium</u><u> </u>= it's gram atomic mass

= 40 g

<u>Mass of one "molecule" of Hydrogen</u>

= it's Gram molecular mass

= gram mass of one atom × number of atoms in one molecule

= 1 × 2

= 2 g

So,

according to our observation:

One atoms of Calcium gives one molecule of Hydrogen <em>(during the particular reaction)</em>

=><u> 40g of Calcium gives = 2g of Hydrogen</u>

•°• 1 g of Calcium gives = \frac{2}{40}

= \frac{1}{20} g Hydrogen

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

<h3><u>Answer</u><u>:</u></h3>

We're provided with 20g of Calcium,

=> 20g of Calcium gives = 20 × \frac{1}{20} g H2

<u>= 1 g H2</u>

_______________

Hope this helps!

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