Chemistry needs an exact knowledge when you discuss about molecular weight of a substance. An excellent question is there Students complete the assignments, but they may confuse in some common questions which needs a proper explanation. A nice question is there as â€œ**How many atoms of copper are in an old penny made of pure copper and weighing 2.15 g?â€ **Now, it is very essential to understand a lot of terms here. Let us understand the answer of this properly.

Avogadroâ€™s number is applicable in this.

Weight of Copper for using in a penny = 2.15 gram.

Now, what is the molar mass of the substance here? So, you need to find out the molar mass and it is 63.55 g/mol

You can also say that 63.55 amu is atomic mass.

So, in 2.15 g there are (2.15 g) / (63. 55g/ mol) = 2.15/ 63.55 mol

Next, it is important to know the number of copper atoms in a single mole.

So, in a mole the number of atoms of copper = 6.022 X 10^{23}

Now, atoms in 2.15 g of copper = 2.15/ 63.55 mol X 6.022 X 10^{23} = 2.04 X 10^{22} atoms

Hence it is clear that there are 2.04 X 10^{22} atoms available in a pure coin of copper weighing 2.15 g.

**What a student should understand?**

One thing is essential to discuss here is just about the Avogadroâ€™s Number. If you have knowledge about that it is very much clear to acquire the solution, but in case you are not able to understand it, then you need to know about that. So, let us know about the law which is the prime part of the solution through which weight and mole of an element are related to each other. Moreover, one essential thing here is just about masses of copper.

Copper is known as an isotope. These are known as Cu-63 and another is Cu-65. Atomic mass of Cu-63 is 62.93 and Cu-65 is 64.93. However, the molar mass which is used to prepare the molar mass of copper is 63.546 amu (atomic mass unit). It is taken as 63.55 amu in case of two points from the decimal.

**Avogadroâ€™s number**

According to the scientist Avogadro** â€“**

**â€œ**The number 6.022 Ã— 10^{23} indicates the number of atoms or molecules in a mole of any substance.â€

Now, you can easily relate this exact number with the number of moles of Cu.

Now, the answer of â€œ**How many atoms of copper are in an old penny made of pure copper and weighing 2.15 g?â€ **is completely ready and clear. it is unknown for many people that old pennies were used Â between the year 1793 and 1857and these were made of pure copper. A lot of students are unable to get this answer and at that time they just contact to the experts.

A lot of other questions are just like this where you may confuse but with proper discussion or with contact to the expert you can easily get it in a proper way.