Chemical formulae

Question 1

What are the prifixes ?

Answer 1

mono- 1
di- 2
tri- 3
tetra- 4
pentra- 5
hexa- 6

e.g) carbon DIoxide

Question 2

What is a mole ?

Answer 2

The mole is a word that represents a number e.g) one mole = 6.022times10

Question 3

What is the Relative Formula Mass ? (RFM)

Answer 3

It is the sum of the relative formula mass of all the atoms shown in the formula.

e.g) Ca=40 N=16 O=16 H=1

Question 4

What is the equation to find the mole ?

Answer 4

Mass

moles Relative formula mass

e.g) How many moles are present in 25g of calcium carbonate?

n (moles) = m/RFM = 25/ 100 (RFM of calcium carbonate) = 0.25moles

Question 5

What formula is used for this question ?

Calculate the mass of calcium chloride produced when 8g of calcium reacts with hydrochloric acid?

Answer 5

Calculations from balanced equations

answer: Ca + 2HCL------- CaCl2 + H2
              1 : 1
              nCa= M/RFM= 8/40 = 0.2moles 
              1 : 1 
              0.2 : 0.2 
              m=N times RFM 
              0.2 times 111 
              =22.2g