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3 years ago

Why was helium absent from mendeleev's original periodic table of 1871?

1 answer:

34kurt3 years ago

6 0

This is because it was not yet discovered during that time. Helium (noble gases) was extremely difficult to discover that time because it does not react with other elements. And now since Mendeleev had based his table on the similar properties of known elements he could not have included Helium in his table.

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Hey plz don't report but what if someone lked my girlhood did I lose my vrginty . I really want someone to eat me. A really good

BARSIC [14]

U got kik?
lets talk first before we go any further

8 0

3 years ago

The basic building blocks of a protein are

snow_lady [41]

The building blocks of protein are amino acids.

Amino acids are a class of organic compounds that contain at least one amino group, -NH2, and carboxyl group, -COOH.

Alpha amino acids , RCH(NH2)COOH, are the building blocks from which proteins are constructed.

The NH group of one amino acid and the COOH group of the other amino acid are joined together and a peptide bond -CONH- is formed between the two amino acids and the product is called a dipeptide.

5 0

2 years ago

Look at the equation CO2 + H2 = CO + H20.

sergejj [24]

Answer:

CO is considered as a product.

Explanation:

A general chemical equation for a combination reaction follows:

To write a chemical equation, we must follow some of the rules:

The reactants must be written on the left side of the direction arrow.

A '+' sign is written between the reactants, when more than one reactants are present.

An arrow is added after all the reactants are written in the direction where reaction is taking place. Here, the reaction is taking place in forward direction.

The products must be written on the right side of the direction arrow.

A '+' sign is written between the products, when more than one products are present.

For the given chemical equation:

are the reactants in the reaction and are the products in the reaction.

Hence, CO is considered as a product.

3 0

2 years ago

Read that From picture and tell me the answer please

Dafna11 [192]

Answer:

1g Hydrogen

Explanation:

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

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

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

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

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

Looking into the equation more carefully, we see:

1 atom of Calcium reacts with 2 molecules of water to give 1 molecule of Calcium Hydroxide alongwith 1 molecule of Hydrogen gas.

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

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

Mass of one atom of Calcium = it's gram atomic mass

= 40 g

Mass of one "molecule" of Hydrogen

= 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 (during the particular reaction)

=> 40g of Calcium gives = 2g of Hydrogen

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

= $\frac{1}{20}$ g Hydrogen

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

<h3>Answer:</h3>

We're provided with 20g of Calcium,

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

= 1 g H2

_______________

Hope this helps!

6 0

2 years ago

The substance that waves travel though?

Sedaia [141]

C) medium.

The medium of a wave is any substance that carries the wave, or through which the wave travels.Ocean waves are carried by water, sound waves are carried by air, and. the seismic waves of an earthquake are carried by rock and soil.

5 0

3 years ago