AS level chemistry question.. titrations HELP PLEASE

Hi any help with the quesstion below is much appricated.

5.125g of washing soda crystals are dissolved and made up to 250cm3 of solution. A 25cm3 portion required 35.8cm3 of 0.0500 mol dm-3 sulphuric acid for neutralisation. Caculate the % of sodium carbonate in the crystals.

Thanks

Reply 1

Revolution is my Name

Work out the number of moles of Sulphuric Acid in the solution (using the equation Moles= Volume x Concentration, and remembering to put the concentration in dm^3). Then write a balanced equation, from which it should become apparent how many moles of Sodium Carbonate are required to react with this number of moles. Then multiply this by 10 to get the number of moles in the full 250cm^3. Then use the equation Mass= Molar Mass x Number of moles, which will give you the mass of Sodium Carbonate in the soda crystals. Then divide this by 5.125, and multiply by 100, to get the Sodium Carbonate in the crystals.

Reply 2

beccajonesy

Revolution is my Name

Any idea what the balanced equation is :s-smilie:

Reply 3

RobG93

Sodium Carbonate + Sulphuric Acid -----> Sodium Sulphate + Carbonate Acid

Na2CO3 + H2SO4 -----> Na2SO4 + H2CO3

Reply 4

Nan8903

why multiplying 10 get your no. of moles in full 250cm³ solution

(edited 3 years ago)

Reply 5

Pigster

Original post by Nan8903

why multiplying 10 get your no. of moles in full 250cm³ solution

Imagine the original 250 cm3 solution had 10 mol in it and you took out 25 cm3 of that solution, it would contain 1 mol.

Now imagine you took 25 cm3 out of a 250 cm3 solution and you found that the 25 cm3 had I don't know 0.0125 mol in. Surely the 250 cm3 would contain 0.125 mol?!?

Reply 6

DavidX123456

Original post by Pigster

Three words : 11 years ago

Reply 7

Pigster

Original post by DavidX123456

Three words : 11 years ago

11 isn't a word and the thread is only ten years old?

I was replying to Nan8903, who was asking a Q about a thread they have somehow found. Perhaps they were doing a past paper with this Q and googled "5.125 g of washing soda crystals" and found this thread.

I usually say something along the lines of "let the dead rest", but was too sleepy this morning to be sarcastic. When people reply to threads giving solutions to an OP from many many years ago, then they get both barrels. My favorite is when people give solutions that are wrong to threads that already have the correct solution posted.

Reply 8

EierVonSatan

Original post by Pigster

Once upon a time, threads would lock after no posts for a number of years. Such as https://www.thestudentroom.co.uk/showthread.php?t=65926 (if you alter the number at the end of the url you'll see that all similar threads are locked - so it wasn't a manual process).

For me the more frustrating ones is where a solution is given in great detail and then someone 10 years later asks a question about it but they haven't bothered to read the thread properly :mad:

Reply 9

frootyfab101

It's quite cool how even after 12 years this thread still isn't locked. It's also quite cool how 12 years later this exact question (from the original post) appeared in my Chemistry lab book.