MYTUTOR SUBJECT ANSWERS

171 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...

3 months ago

Answered by Kristina, a GCSE Chemistry tutor with MyTutor


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

211 SUBJECT SPECIALISTS

£30 /hr

Beth S.

Degree: Biosciences (Masters) - Durham University

Subjects offered: Chemistry, Biology

Chemistry
Biology

“Hi, I'm Beth and I'm a first year undergraduate at Durham University studying Biosciences! I have an interest in all things science and would love to share my passion and understanding with others. I like to think I can take ideas from...”

MyTutor guarantee

£20 /hr

Effie H.

Degree: Geography (Bachelors) - Durham University

Subjects offered: Chemistry, Geography+ 1 more

Chemistry
Geography
Biology

“About Me:I am a Geography student at Durham University. I have always loved Geography, and this was encouraged by some amazing teachers at school and now lecturers at University. I hope I can get you as excited about the subject!I ...”

£18 /hr

Charles W.

Degree: Chemistry (Bachelors) - University College London University

Subjects offered: Chemistry, Maths+ 1 more

Chemistry
Maths
Biology

“Friendly approachable tutor with well thought out tutorials combined with excellent exam techniques”

MyTutor guarantee

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 ...”

You may also like...

Other GCSE Chemistry questions

Why does HCl dissociate in water but not in methylbenzene?

Explain the atomic structure of an Atom?

What is the volume of carbon dioxide released at room temperature and pressure when 6.2 g of copper carbonate reacts with excess dilute sulfuric acid?

Describe and explain the trend in reactivity of the alkali metals (Group 1)

View GCSE Chemistry tutors

Cookies:

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

mtw:mercury1:status:ok