Question

how many molecules are in 25. 0
g of H/2SO/4

Answer 1

Mass of $\bf H_2SO_4$ is 25 g and we are asked to find number of molecules present in 25 g of $\bf H_2SO_4$

$\qquad$$\pink{\bf\longrightarrow { Molar \:mass \:of \:H_2SO_4:-} }$

$\qquad$$\bf \longrightarrow 1\times2 +32 +16\times 4$

$\qquad$$\bf \longrightarrow 98$

$\qquad$____________________

Let's calculate the number of moles present in 25 g of $\bf H_2SO_4$

$\qquad$$\purple{\bf\longrightarrow { No \:of \:moles = \dfrac{Given \:mass}{Molar\: mass}}}$

$\qquad$$\bf \longrightarrow \dfrac{25}{98}$

$\qquad$$\bf\longrightarrow 0.2551\: moles$

We know –

• Avogadro number = 6.022×10²³

Number of molecules:-

$\qquad$$\purple{\bf \longrightarrow No \: of \: moles \times Avogadro \: number}$

$\qquad$$\bf \longrightarrow 0.2551×6.022×10²³$

$\qquad$$\bf \longrightarrow 1.54 \times 10^{23}$

.

$\qquad$____________________

Answer 2

Taking into account the definition of Avogadro's number and molar mass, 1.5359×10²³ molecules are in 25 g of H₂SO₄.

Avogadro's Number

Avogadro's Number or Avogadro's Constant is called the number of particles that make up a substance (usually atoms or molecules) and that can be found in the amount of one mole of said substance. Its value is 6.023×10²³ particles per mole. Avogadro's number applies to any substance.

Definition of molar mass

The molar mass of substance is a property defined as its mass per unit quantity of substance, in other words, molar mass is the amount of mass that a substance contains in one mole.

The molar mass of a compound (also called Mass or Molecular Weight) is the sum of the molar mass of the elements that form it (whose value is found in the periodic table) multiplied by the number of times they appear in the compound.

Molar mass of H₂SO₄

In this case, you know the molar mass of the elements is:

• S= 32 g/mole
• O= 16 g/mole
• H= 1 g/mole

So, the molar mass of the compound H₂SO₄ is calculated as:

H₂SO₄= 2× 1 g/mole + 32 g/mole + 4× 16 g/mole=

Solving:

H₂SO₄= 98 g/mole

Amount of moles that contain 25 g of H₂SO₄

You can apply the following rule of three: if 98 grams of the compound are contained in 1 mole, 25 grams are contained in how many moles?

$amount of moles= \frac{25 gramsx1 mole}{98 grams}$

amount of moles= 0.255 moles

25 grams are contained in 0.255 moles of H₂SO₄.

Amount of molecules that contain 25 g of H₂SO₄

Finally you can apply the following rule of three, taking into account the Avogadro's Number: If 1 mole of the compound contains 6.023×10²³ molecules, 0.255 mole of the compound contains how many molecules?

amount of molecules= (6.023×10²³ molecules × 0.255 mole)÷ 1 mole

amount of molecules= 1.5359×10²³

Finally, 1.5359×10²³ molecules are in 25 g of H₂SO₄.

Learn more about

Avogadro's Number:

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Molar mass:

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