Example 2 –
 Calculate the percentage of copper present in the copper ore malachite ()
 1. Firstly, we must find the relative atomic masses (RFM):
 Cu = 64gmol 1
 C = 12gmol 1
 O =16gmol 1
 H = 1gmol 1
 2. Then we calculate the M r of :
3. Now we have the RFM, we need to work out the amount of copper (Cu) in the formula. Cu has a mass of 64 and there are two atoms giving a total mass of 128 gmol 1
4. Finally, we can work out the percentage of copper in malachite by using our formula:
: Relative formula mass
Contents
 0.1 What is the relative formula mass RFM?
 0.2 Why do we calculate relative atomic mass?
 0.3 Is RFM and RAM the same?
 0.4 What is the relative formula mass of NaOH?
 1 What is MgCl 2 relative formula mass?
 2 How to calculate atomic mass?
 3 How is relative atomic mass of an atom measure?
 4 What is relative atomic mass with example?
 5 What is the relative of mass?
What is the relative formula mass RFM?
How to calculate relative formula mass relative molecular mass calculating RFM RMM of compound formula gcse chemistry calculations igcse KS4 science A level GCE AS A2 O Level practice questions exercises How to calculate relative formula mass or relative molecular mass RFM/RMM or just M r
 How do I calculate relative molecular mass? RMM
 How to calculate relative formula mass? RFM
 Is there any difference between RMM and RFM?
 Does it matter whether the compound is ionic or covalent?
 The relative molecular mass/relative formula mass is defined as the sum of all the individual atomic masses of ALL the atoms in the formula (M r ).
 If the individual atomic masses of all the atoms in a formula are added together you have calculated the relative formula mass
 Atomic masses are listed at the bottom of the page
e.g. for ionic compounds e.g. NaCl = 23 + 35.5 58.5) or molecular mass for covalent elements or compounds,e.g. M r of N 2 = 28 from (2 x 14) or compounds e.g. M r of C 6 H 12 O 6 = 180 from,
 and more examples of how to calculate relative formula mass are further down the page, you get atomic masses from your periodic table.
 In a balanced chemical symbol equation, the total of relative formula masses of the reactants is equal to the total relative formula masses of the products (see ).
 To be honest, the term relative formula mass can be used with any compound whether it be ionic or covalent – it just seems NOT correct to talk about the molecular mass of an ionic compound when it doesn’t consist of molecules, but is that one for the purists!
 The shorthand M r can be used for the formula of any element or compound and to repeat, ‘it doesn’t matter whether a compound is ionic or covalent ‘.
Numerically M r = Relative formula mass = relative molecular mass = the sum of all the atomic masses for ALL the atoms in a given formula BUT, note, The term relative formula mass is usually applied to ionic compounds. The term relative molecular mass is usually applied to covalent compounds i.e.
 Whereas relative atomic mass (section ) only applies to a single atom, anything with at least two atoms in the formula requires the term relative formula mass or relative molecular mass to be used.
 WARNING: The most common error is to use atomic/proton numbers instead of atomic masses, unfortunately, except for hydrogen, they are different !
 Examples of relative formula mass or relative molecular mass calculations:
 How to calculate relative molecular mass = How to calculate relative formula mass
 Molecular/formula mass = total of all the atomic masses of ALL the atoms in the molecule/compound.
Watch out for brackets e.g. (OH) 2 means two OH groups to add up!
 Relative molecular mass calculation Example 2.1
 The diatomic molecules of the elements hydrogen H 2 and chlorine Cl 2
 relative atomic masses, Ar : H = 1, Cl = 35.5
 Formula masses, RMM or M r
 relative molecular mass for hydrogen H 2 = 2 x 1 = 2
 relative molecular mass for chlorine Cl 2 = 2 x 35.5 = 71 respectively.
 Relative molecular mass calculation Example 2.2
 T he element phosphorus consists of P 4 molecules. (atomic mass of P = 31)
 relative molecular mass or M r of phosphorus = 4 x its atomic mass = 4 x 31 = 124
 Relative molecular mass calculation Example 2.3: The compound water H 2 O
 relative atomic masses are H=1 and O=16
 relative molecular mass or M r = (1×2) + 16 = 18 (molecular mass of water)
 Relative molecular mass calculation Example 2.4
 The compound sulphuric acid H 2 SO 4 when pure, is a covalent compound
 relative atomic masses are H = 1, S = 32 and O = 16
 relative molecular mass or M r = (1 x 2) + 32 + (4 x 16) = 98 (molecular mass of sulphuric acid )
 Relative formula mass calculation Example 2.5
 The ionic compound magnesium hydroxide Mg(OH) 2 (ionic)
 relative atomic masses are Mg = 24, H = 1 and O = 16
 relative formula mass or M r = 24 + 2 x (16+1) = 58
 Important note on terminology
 The term relative formula mass is also best applied to giant structure compounds
 e.g. silicon dioxide SiO 2 (RFM = 28 + 16 + 16 = 60, a 3D giant covalent lattice compound.
 The term relative formula mass is also best applied to giant structure compounds
 Relative formula mass calculation Example 2.6
 The ionic compound aluminium oxide (Al 3+ ) 2 (O 2 ) 3 or just the plain formula Al 2 O 3
 but it makes no difference to the calculation of relative formula mass or relative molecular mass.
 relative atomic masses are Al = 27 and O = 16
 so the relative formula mass RFM or M r = (2 x 27) + (3 x 16) = 102
 Relative formula mass calculation Example 2.7
 Calcium phosphate is also ionic but a more tricky formula to work out!
 (Ca 2+ ) 3 (PO 4 3 ) 2 or Ca 3 (PO 4 ) 2, but it makes no difference to the calculation of relative formula mass or relative molecular mass.
 atomic masses: Ca = 40, P = 31, O =16
 relative formula mass or M r = (3 x 40) + 2 x = (120) + (2 x 95) = 310
 Relative molecular mass calculation Example 2.8
 Glucose C 6 H 12 O 6 a covalent compound
 atomic masses: C = 12, O= 16, H = 1
 relative molecular mass of glucose M r ( C 6 H 12 O 6 ) = (6 x 12) + (12 x 1) + (6 x 16) = 180
 Relative molecular mass calculation Example 2.9
 butane C 4 H 10
 relative atomic masses: C = 12, H=1
 M r = (4 x 12) + (10 x 1) = 58
 Relative formula mass calculation Example 2.10
 copper(II) sulfate (copper sulfate, CuSO 4, ionic)
 relative atomic masses: Cu = 63.5, S = 32, O = 16
 M r = 63.5 + 32 + (4 x 16) = 159.5 (its 160 is you use Cu = 64)
 Relative molecular mass calculation Example 2.11
 propanol, C 3 H 8 O, CH 3 CH 2 CH 2 OH (the same formula can be expressed in different ways!)
 relative atomic masses: C = 12, H=1, O = 16
 M r = (3 x 12) + (8 x 1) + 16 = 60
 Relative formula mass calculation Example 2.12
 magnesium nitrate, Mg(NO 3 ) 2
 relative atomic masses: Mg = 24, N = 14, O = 16
 M r = 24 + (2 x 14) + (6 x 16) = 24 + 28 + 96 = 148
 Relative formula mass calculation Example 2.13
 blue hydrated copper sulfate crystals CuSO 4,5H 2 O, again a bit more tricky!
 Cu = 63.5, S = 32, H = 1, O =16
 Just do this carefully in parts eg
 CuSO 4 = 63.5 + 32 + (4 x 16) = 159.5 (160 if you use Cu = 64)
 H 2 O = (2 x 1) + 16 = 18, 5 x 18 = 90
 Formula mass = 159.5 + 90 = 249.5 (250 if Cu = 64)
Selfassessment Quizzes on relative formula mass or relative molecular mass
 Above is typical periodic table used in GCSE sciencechemistry specifications in calculating relative formula mass or calculating relative molecular mass, and I’ve ‘usually’ used these values in my exemplar calculations to cover most syllabuses
OTHER CALCULATION PAGES
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Is Mr and RFM the same?
C) Relative Formula Mass, Mr – The relative formula mass of an ionic compound is the average mass of one unit of that ionic compound compared to 1/12 of the mass of one carbon12 atom. Ionic compounds such as sodium chloride and magnesium oxide do no exist as molecules.
Why do we calculate relative atomic mass?
Calculating Relative Atomic Mass – In order to perform accurate chemical calculations, relative atomic mass must be used rather than an individual mass number. As a result, relative atomic mass takes into account all of the naturally occurring stable isotopes of an element.
 The mass numbers of its isotopes
 The abundance of these isotopes
 The formula that can be used to calculate the relative atomic mass:
 \(\begin A_ = \frac \end \)
 Question.
 Based on the
 \(\begin _ ^ \textrm \ and\ _ ^ \textrm \end \)
 Calculate the relative atomic mass of chlorine.
 Solution –
 Chlorine is made up of two isotopes, 75 % chlorine – 35 and 25 %chlorine – 37.
 The average mass is calculated as
 \(\begin A_ = \frac \end \)
 \(\begin A_ = \frac = 35.5\end \)
isotopes, As a result, the relative atomic mass of chlorine is 35.5, also known as RAM or A r (Cl) = 35.5.
 Question.
 Based on the
 \(\begin _ ^ \textrm \ and\ _ ^ \textrm \end \)
 Solution.
 Bromine is made up of two isotopes, 50 % 79 Br and 50 % 81 Br.
 The average mass / relative atomic mass is calculated as
 \(\begin A_ = \frac \end \)
 \(\begin A_ = \frac = 80\end \)
 As a result, the relative atomic mass of bromine is 80.
, calculate the relative atomic mass of bromine.
Is RFM and RAM the same?
RFM – RFM stands for relative formula mass (Mr). This is the sum of the RAMs of all the elements in a molecule.I.e. it is the mass of the molecule. These two measurements are used in Chemistry because it is more accurate.
How to calculate relative molecular mass from mass spectrum?
Finding the relative formula mass (relative molecular mass) from a mass spectrum is therefore trivial. Look for the peak with the highest value for m/z, and that value is the relative formula mass of the compound. There are, however, complications which arise because of the possibility of different isotopes (either of carbon or of chlorine or bromine) in the molecular ion. These cases are dealt with on separate pages.What is the relative formula mass of NaOH?
Relative formula mass calculations – The table shows some more examples of relative formula mass calculations, using the relative atomic mass values listed beneath it.
Compound  Formula  Calculation  Relative formula mass 

Water  H 2 O  1 + 1 + 16 =  18 
Sodium hydroxide  NaOH  23 + 16 + 1 =  40 
Magnesium hydroxide  Mg(OH) 2  24 + 16 + 16 + 1 + 1 = (remember that there are two of each atom inside the brackets)  58 
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What is MgCl 2 relative formula mass?
Amounts of Substances – GCSE Chemistry (Combined Science) AQA Revision – Study Rocket
 Calculating relative formula mass
 The relative formula mass is JUST the relative atomic mass of all of the atoms in the molecule added up.
 Example 1 : Magnesium Chloride
MgCl2 has a relative formula mass of 95 since there is one Magnesium (atomic mass 24) and two chloines (each with atomic mass of 35.5). Relative Formula Mass of MgCl2 = 24 + 35.5 + 35.5 = 95
 Example 2 : Dihydrogen Monoxide (Water)
 H2O has a relative formula mass of 18 since there is one Oxygen (atomic mass 16) and two Hydrogen atoms (each with atomic mass of 1).
 Relative Formula Mass of H2O = 1 + 1 + 16 = 18
What is relative mass of an atom?
Publisher Summary – This chapter discusses the relative atomic masses, molecular masses, and the mole concept. The relative atomic mass of an element is defined as the weight in grams of the number of atoms of the element contained in 12.00 g of carbon12.
 To calculate the relative atomic mass of chlorine, the average mass of one atom of chlorine is found by considering 100 atoms of chlorine.75.53 of these atoms each have a mass of 35 atomic mass units (AMU), and 24.47 atoms each have a mass of 37 AMU.
 The word mole has been adopted to represent the Avagadro number of atoms of an element, that is, the relative atomic mass of an element.
Thus, one mole of sodium weighs 23.0 g or one tenth of a mole of sodium weighs 2.3 g. Read full chapter URL: https://www.sciencedirect.com/science/article/pii/B9780750616836500564
How to calculate atomic mass?
Fundamental properties of atoms including atomic number and atomic mass. The atomic number is the number of protons in an atom, and isotopes have the same atomic number but differ in the number of neutrons. Radioactivity pops up fairly often in the news.
 For instance, you might have read about it in discussions of nuclear energy, the Fukushima reactor tragedy, or the development of nuclear weapons.
 It also shows up in popular culture: many superheroes’ origin stories involve radiation exposure, for instance—or, in the case of SpiderMan, a bite from a radioactive spider.
But what exactly does it mean for something to be radioactive? Radioactivity is actually a property of an atom. Radioactive atoms have unstable nuclei, and they will eventually release subatomic particles to become more stable, giving off energy—radiation—in the process.
 Often, elements come in both radioactive and nonradioactive versions that differ in the number of neutrons they contain.
 These different versions of elements are called isotopes, and small quantities of radioactive isotopes often occur in nature.
 For instance, a small amount of carbon exists in the atmosphere as radioactive carbon14, and the amount of carbon14 found in fossils allows paleontologists to determine their age.
In this article, we’ll look in more detail at the subatomic particles that different atoms contain as well as what makes an isotope radioactive. Atoms of each element contain a characteristic number of protons. In fact, the number of protons determines what atom we are looking at (e.g., all atoms with six protons are carbon atoms); the number of protons in an atom is called the atomic number,
In contrast, the number of neutrons for a given element can vary. Forms of the same atom that differ only in their number of neutrons are called isotopes, Together, the number of protons and the number of neutrons determine an element’s mass number : mass number = protons + neutrons. If you want to calculate how many neutrons an atom has, you can simply subtract the number of protons, or atomic number, from the mass number.
A property closely related to an atom’s mass number is its atomic mass, The atomic mass of a single atom is simply its total mass and is typically expressed in atomic mass units or amu. By definition, an atom of carbon with six neutrons, carbon12, has an atomic mass of 12 amu.
 Other atoms don’t generally have roundnumber atomic masses for reasons that are a little beyond the scope of this article.
 In general, though, an atom’s atomic mass will be very close to its mass number, but will have some deviation in the decimal places.
 Since an element’s isotopes have different atomic masses, scientists may also determine the relative atomic mass —sometimes called the atomic weight —for an element.
The relative atomic mass is an average of the atomic masses of all the different isotopes in a sample, with each isotope’s contribution to the average determined by how big a fraction of the sample it makes up. The relative atomic masses given in periodic table entries—like the one for hydrogen, below—are calculated for all the naturally occurring isotopes of each element, weighted by the abundance of those isotopes on earth.
Extraterrestrial objects, like asteroids or meteors, might have very different isotope abundances. As mentioned above, isotopes are different forms of an element that have the same number of protons but different numbers of neutrons. Many elements—such as carbon, potassium, and uranium—have multiple naturally occurring isotopes.
A neutral atom of Carbon12 contains six protons, six neutrons, and six electrons; therefore, it has a mass number of 12 (six protons plus six neutrons). Neutral carbon14 contains six protons, eight neutrons, and six electrons; its mass number is 14 (six protons plus eight neutrons).
 These two alternate forms of carbon are isotopes.
 Some isotopes are stable, but others can emit, or kick out, subatomic particles to reach a more stable, lowerenergy, configuration.
 Such isotopes are called radioisotopes, and the process in which they release particles and energy is known as decay,
Radioactive decay can cause a change in the number of protons in the nucleus; when this happens, the identity of the atom changes (e.g., carbon14 decaying to nitrogen14). Radioactive decay is a random but exponential process, and an isotope’s halflife is the period over which half of the material will decay to a different, relatively stable product.
The ratio of the original isotope to its decay product and to stable isotopes changes in a predictable way; this predictability allows the relative abundance of the isotope to be used as a clock that measures the time from the incorporation of the isotope (e.g., into a fossil) to the present. For example, carbon is normally present in the atmosphere in the form of gases like carbon dioxide, and it exists in three isotopic forms: carbon12 and carbon13, which are stable, and carbon14, which is radioactive.
These forms of carbon are found in the atmosphere in relatively constant proportions, with carbon12 as the major form at about 99%, carbon13 as a minor form at about 1%, and carbon14 present only in tiny amounts start superscript, 1, end superscript,
 As plants pull carbon dioxide from the air to make sugars, the relative amount of carbon14 in their tissues will be equal to the concentration of carbon14 in the atmosphere.
 As animals eat the plants, or eat other animals that ate plants, the concentrations of carbon14 in their bodies will also match the atmospheric concentration.
When an organism dies, it stops taking in carbon14, so the ratio of carbon14 to carbon12 in its remains, such as fossilized bones, will decline as carbon14 decays gradually to nitrogen14 squared, After a halflife of approximately 5,730 years, half of the carbon14 that was initially present will have been converted to nitrogen14.
This property can be used to date formerly living objects such as old bones or wood. By comparing the ratio of carbon14 to carbon12 concentrations in an object to the same ratio in the atmosphere, equivalent to the starting concentration for the object, the fraction of the isotope that has not yet decayed can be determined.
On the basis of this fraction, the age of the material can be calculated with accuracy if it is not much older than about 50,000 years. Other elements have isotopes with different half lives, and can thus be used to measure age on different timescales.
How is relative atomic mass of an atom measure?
Definition. Relative atomic mass is determined by the average atomic mass, or the weighted mean of the atomic masses of all the atoms of a particular chemical element found in a particular sample, which is then compared to the atomic mass of carbon12.
What is relative atomic mass with example?
Conclusion – The “fundamental building blocks of matter” are described as atoms. It is the lowest component of matter that possesses chemical elemental characteristics. Single or more atoms are joined together by covalent (chemical) bonds to form molecules.
Atoms can be represented by circle shapes, each of which has a nucleus at the center.Relative atomic mass (RAM or Ar) is the weighted average of an element’s isotopes’ masses in relation to the mass of a carbon12 atom. For example, the relative atomic mass of oxygen is 15.999 u. Here we discussed how to calculate the relative atomic mass of elements, and the relative atomic mass formula for calculating it was also discussed.
It is a unitless quantity as it is a ratio. : Relative Atomic Mass and Its Calculation – Important Concepts and Tips for JEE
What is the simple definition of relative formula mass?
Be careful with things which contain water of crystallisation like the copper(II) sulfate crystals in this example. Add the water up first and then multiply it by 5 (or whatever other number you need). If you try to do it as hydrogen and oxygen separately, you stand a good chance of getting it wrong. Students usually remember to multiply the 2 hydrogens by 5, but forget to multiply the oxygen by 5. If you add the water up as a whole, that can’t happen. Defining the relative formula mass I find it hard to imagine an exam question in which you were asked to define relative formula mass rather then just work it out, but just in case,, Either:The relative formula mass of a substance is the weighted average of the masses of the formula units on a scale on which a carbon12 atom has a mass of exactly 12 units.
Or:
The relative formula mass of a substance is the weighted average of the masses of the formula units relative to 1/12 of the mass of a carbon12 atom.
The “formula unit” is just the formula as you have written it. Go to the Section 1 Menu,, To return to the list of learning outcomes in Section 1 Go to the CIE Main Menu,, To return to the list of all the CIE sections Go to Chemguide Main Menu,, This will take you to the main part of Chemguide.
What is the relative mass scale?
RELATIVE ATOMIC MASS A relative scale is one in which all measurements are compared to one standard or reference measure. The advantage of a relative scale is that very large or very small numbers can be compared relatively easy. Carbon is not toxic in any way.
What is the relative of mass?
What does relative mass indicate? A relative atomic mass (also known as atomic weight; symbol: A r ) indicates how many times an average atom of an element in a given sample is heavier than onetwelfth of an atom of carbon12.
What is the definition of Mr in chemistry?
Calculating relative formula mass – Relative formula mass has the symbol, M r, To calculate M r for a substance:
 work out how many atoms of each element are in the chemical formula
 add together the A r values for all the atoms of each element
For example, the formula for carbon dioxide is CO 2, It has one carbon atom ( A r = 12) and two oxygen atoms ( A r = 16): M r of CO 2 = 12 + 16 + 16 = 44 It could also be calculated this way: N r of CO 2 = (1 × 12) + (2 × 16) = 12 + 32 = 44 Like A r values, M r values also have no units.