# Relative atomic mass and relative atomic formula Watch

• Slides: 15

Relative atomic mass and relative atomic formula

Watch the video and answer the questions 1. Where will you find the relative atomic mass for an element? 2. How do you work out the relative formula mass? 3. Why is the relative formula mass for Water (H 2 O) 18 and not 17? https: //www. youtube. com/watch? v=it_f. MQu 5 ivg

Relative Atomic Mass Ar Scientists discuss the mass if an atoms relative to the mass of a Carbon atom. The mass of a carbon atom is given as 12 and the mass of other atoms are then calculated from this. This is called the relative atomic mass (Ar) Why doesn't it have any units?

E. g. (1 x 2) = 2 16 18 Complete the table using the periodic table on the next slide. Don’t forget to time the mass number by the number of atoms present for each element if there is more than one.

Calculating percentage composition We can calculate what percentage of a compound is made up out of each type of element. Step 1: make it a fraction (Ar /Mr) Step 2: multiply by 100 Percentage of Element in compound = Total Ar of Element in a molecule x 100 Mr of compound

Calculating percentage composition Using your answers from task one to help you, calculate the percentage composition of the following compounds. Formula H 2 O HCl Na. Cl SO 2 CO 2 Na. OH Relative atomic masses Ar H = (1 x 2) = 2 O = 16 H= Cl = Na = Cl = S= O= C= 0= Relative formula mass Mr 18 Percentage composition Of O Of H Of Na Of S Of O Of Na Challenge: Fe 2 O 3 Of Fe Ca. CO 3 Of Ca C 6 H 12 O 6 Of H Cu(OH)2 Of O 16 18 X 100 = 89%