titration questions again

could anyone tell me how to even approach these questions? it looks like i have completely forgotten how to do them over the holiday

13. 8.580g of washing soda (Na2CO3.xH2O) were made up to 250.0cm3 of aqueous solution. 25.00cm3 of this solution required 30.00cm3 of 0.2000moldm-3 hydrochloric acid for neutralisation. Calculate x in the formula Na2CO3.XH2O.

14. In standardising a rougly 0.05moldm-3 sulphuric acid solution, 1.325g of anhyrdrous sodium carbonate solution was made up to 250.0cm3 and 25.00cm3 of this solution needed 23.50cm3 of the acid. Calculate the concentration of the acid in g/dm3. How many cm3 of water must be added to 1000cm3 of this acid to make it exactly 0.05000M?

15. 2.500g of a mixture of anhydrous sodium carbonate and sodium chloride were made up to 250.0cm3 with distilled water. 25.00cm3 of this solution required 20.00cm3 of 0.1000moldm-3 hydrochloric acid. Calculate the percentage by mass of soidum chloride in the mixture.

any replies will be helpful :smile:

Reply 1

MetroGnome

I'm not going to try the questions, but as long as you use these formulae it should be okay..

Moles = mass/relative atomic mass

Concentration in moldm-3 = (moles of solute / volume in cm3) x 1000

They can be rearranged so you find mass from moles and Mr etc.
The x 1000 bit is just the conversion to decimeters.. some people might do it differently but that way seems to suit the question

I think it's just the wording of the questions that's making them seem scary :P
What I do is rewrite them in a better order, like write the substances and what they make and then beneath each write any info you're given (like mass or whatever). It's kinda handy as the numbers are easier to plug into the calculations =)