# Chemical calulations

This will give you all the chemical calulations that are needed in unit 2 Chemistry higher tier

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## Relative fomula mass (Mr)

The relative formula mass is the mass of a compouns, It is calulated by adding up the masses of all the atoms.

Eg1)  LiF
Mass of Li=  7
Mass of F=19

7+19=26 <- relative fomula mass

Eg2) H20
Mass of H2= 2
Mass of O= 16

2+16= 26 <- relative formula mass.

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## Percentage mass

Percentage mass is a way to describe what proportians of the different element there are in a compound

Step 1) Work out the total mass of the compound
Step 2) Divide the mass of the element by the total mass of the compound.
Step 3) Express percentage by multiplying it by 100.

Eg1) What is the percentage mass of H in H20?

Step 1) H2= 2 O=16   2+16=18

Step 2)  Mass of H2=2.  Mass of H20 is 18
2/18

Step 3) 2/18 x 100= 11.11% <-- percentage mass!

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## Percentage mass continued

Eg2) What is the percentage mass of O in NaOH?

Step 1) Na= 23 O= 16 H=1
23+16+1= 40

Step 2) Mass of O=16. Mass of NaOH= 40
16 / 40

Step 3) 16 / 40 x 100 = 40% <-- percentage yeild

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## Moles

A mole is an expression that tells us how many ions or atoms or molecules we have,

The mass of a mole of any substance is equivalent to its atomic mass.
It is expressed in grams

eg1) the mole is 1 sodium is 23 grams.

eg2) The mole of 10 Chlorine is 35 grams.

eg3) The mole of 0.1 Ionine atoms is 12.7 grams.

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