Quantitative Chemistry and solutions

Mole concentraiton(mol/dm3) = No. of moles/Volume(dm3) 

OR

Mass-concentration(g/dm3)= Mass(g)/Volume(dm3)   

Q. How many moles of sodium chloride are in 250cm3 of a 3 mol/dm3 solution of NaCl?

A. No. of Moles = C x V ---> 3 x 0.25 = 0.75 moles NOTE-Convert 250cm3 into dm3 so 0.25

Converting: Mass con. = Mol con. x Mr 

Q. Find the mass con. of a 2mol/dm3 solution of H2SO4 (H=1, S=32, O=16)

A. 2 x (2 + 32 + 64) = 196 g/dm3

Moles = Con x Vol

Q. You start of with 25cm3 of sodium hydorxide in your flask, and you know that its con. is 0.1 mol/dm3. You find from your titration that it takes 30cm3 of sulphuric acid to neutralise the sodium hydroxide. Find the con. of the acid. 

1) Work out the moles of the sodium hydroxide:(25/1000) x 0.1= 0.0025 moles

2) 2NAOh + H2SO4 --> Na2SO4 + 2H2O Mole ratio 2:1 so 0.0025/2 = 0.00125 moles of sulphuric acid.

3) C = M x V   So 0.00125 x (30/1000)= 0.0417m/dm3