MYTUTOR SUBJECT ANSWERS

697 views

What does Avogadro's number mean?

Avogadro's number is simply used as a way of telling us how much of a substance we have. 

The number is 6.022 x 1023, and if we have that number of particles, we can make it easier by saying we have one mole of particles. The particles could be atoms of an element, molecules of a compound, or even sweets in a jar (but in Chemistry you'll only really be dealing with compounds and elements!)

For example, instead of saying we have 1.044 x 1024 atoms, its easier to say that we have 2 moles of atoms ([1.044 x 1024 ] / [6.022 x 1023] = 2), because the number is smaller and more manageable.

The reason Avogadro's number is so important is because it is the number of atoms in one mole of atoms- and the definition of a mole is the number of Carbon-12 atoms present in 12 grams of Carbon-12

This means if we have one mole of carbon-12 atoms (which have a relative atomic mass of 12), we have 12 grams of it. So Avogadro's number is used primarlily to convert between mass of a substance in grams, and the mass of a substance in terms of relative atomic mass (Ar), or relative molecular mass (Mr) if it's a compund.

The relationship is: number of moles = mass (g) / Ar

If we plug in the values from the definition, we see that the definition is consistent with the equation:

number of moles = 12 / 12 

                          = 1 mole

We can use this equation for any solid substance with a known atomic (or molecular) mass. For example:

Calculating the number of moles in 85g of Magnesium solid-

number of moles (n)= mass / Ar of magnesium

                          n = 85 / 24

                             = 3.5 mol (to 1 decimal place)

We can also use the equation for compounds, but we need to add up the Ars of each component to find the overall Mr.

E.g. 20g of NaOH(s). [NB: Mr of NaOH  = 23 + 16 + 1 = 40]

n = 20 / 40

   = 0.5 mol

Kristina F. GCSE Chemistry tutor, GCSE Maths tutor, A Level Chemistry...

10 months ago

Answered by Kristina, a GCSE Chemistry tutor with MyTutor


Still stuck? Get one-to-one help from a personally interviewed subject specialist

358 SUBJECT SPECIALISTS

£18 /hr

Rhiannon M.

Degree: Environmental Geoscience (Bachelors) - Durham University

Subjects offered:Chemistry, Maths+ 2 more

Chemistry
Maths
Geology
Geography

“Third year Earth Sciences student at Durham; specialise in geochemistry and tutor in Earth sciences, Chemistry and Maths”

Trusted by schools

|  4 completed tutorials

Vijay G. GCSE Biology tutor, A Level Extended Project Qualification t...
£20 /hr

Vijay G.

Degree: Medicine (Bachelors) - Queen Mary, London University

Subjects offered:Chemistry, Extended Project Qualification+ 3 more

Chemistry
Extended Project Qualification
Biology
-Personal Statements-
-Medical School Preparation-

“Enthusiastic 4th year Medical student with a background of tutoring for GCSE, A level and University applications including entrance exams.”

£22 /hr

Eleanor H.

Degree: Biochemistry (Bachelors) - Bristol University

Subjects offered:Chemistry, Maths+ 1 more

Chemistry
Maths
Biology

“ABOUT ME: I am a biochemistry student, currently studying at the University of Bristol, and have had a passion for the natural sciences from a very young age. I am patient, hardworking and experienced, having tutored students in Maths...”

About the author

Kristina F.

Currently unavailable: for new students

Degree: Chemistry (Masters) - Durham University

Subjects offered:Chemistry, Maths

Chemistry
Maths

“Hi! I'm Kristina, and I've just started studying my favourite subject, Chemistry, at Durham University. I'm passionate about science and maths as I enjoy challenges and problem-solving, and I love to learn about how amazing our world ...”

MyTutor guarantee

|  2 completed tutorials

You may also like...

Other GCSE Chemistry questions

When chlorine is bubbled through potassium bromide solution, the solution turns orange. Explain this.

How is crude oil separated into fractions?

What exactly is a mole of something?

What is the difference between the atomic number and the mass of an element?

View GCSE Chemistry tutors

We use cookies to improve your site experience. By continuing to use this website, we'll assume that you're OK with this. Dismiss

mtw:mercury1:status:ok