Question

How many chromium atoms in a $5.67.g$ mass of chromium metal?

Answer 1

One mole of anything, including atoms, is $6.022 \times {10^{23}}$ which is known as Avogadro’s number of them. To find the number of atoms we will multiply the given mass by the reciprocal of the molar mass.

Complete Step By Step Answer:
Number of atoms is calculated using a number known as “Avogadro’s Number”. First we will find the atomic mass of chromium it can get from the periodic table. So, the atomic mass of chromium is: ${52_{}}{g_{}}mo{l^{ - 1}}$ , this atomic mass is numerically equal to the molar mass in grams/mole, and this means chromium is ${52_{}}{g_{}}mo{l^{ - 1}}$ .
Another property of Avogadro’s number is that the mass of one mole of a substance is equal to that substance’s molecular weight.
Now, we will change into moles using the molar mass of chromium, the Number of moles will be:
${5.67_{}}o{f_{}}Cr \times \dfrac{{{1_{}}mol{e_{}}Cr}}{{52.0}} = 0.109mol$ Of chromium.
Once the amount of moles is known, the number of atoms in the formula may be calculated using Avogadro’s number. Thus, $0.10mol \times 6.022 \times {10^{23}} = 0.65 \times {10^{23}}$ atoms.
So, there are $0.65 \times {10^{23}}$ atoms in ${52_{}}{g_{}}mo{l^{ - 1}}$ of chromium.
This can be written without a fraction in the denominator by multiplying the number of atoms by the reciprocal of Avogadro’s number if we know the number of atoms and need to change in moles.

Note:
To convert moles to molecules, we need to know the weight of the sample, the sum of its atomic masses from the periodic table and a constant known as Avogadro’s number. Avogadro’s number is named after Amedeo Avogadro. An Italian scientist hypothesized that equal volumes of gases at the same temperature and pressure will have the same number of particles.