The Student Room Group
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>
Competition - post a photo you've taken of nature >>

amount of substance hekp

A student added 627 mg of hydrated sodium carbonate (Na2CO3.xH2O) to 200 cm3of 0.250 mol dm–3 hydrochloric acid in a beaker and stirred the mixture. After the reaction was complete, the resulting solution was transferred to a volumetric flask, made up to 250 cm3 with deionised water and mixed thoroughly.Several 25.0cm3 portions of the resulting solution were titrated with 0.150 mol dm–3 aqueoussodium hydroxide. The mean titre was 26.60 cm3 of aqueoussodium hydroxide.Calculate the value of x in Na2CO3.xH2O Show your working.Give your answer as an integer.[7 marks]

I have worked out the moles for HCl (0.05) and for NaOH (3.99x10^-2)

What do I do now lol
(edited 5 years ago)
Original post by anactualmess
A student added 627 mg of hydrated sodium carbonate (Na2CO3.xH2O) to 200 cm3of 0.250 mol dm–3 hydrochloric acid in a beaker and stirred the mixture. After the reaction was complete, the resulting solution was transferred to a volumetric flask, made up to 250 cm3 with deionised water and mixed thoroughly.Several 25.0cm3 portions of the resulting solution were titrated with 0.150 mol dm–3 aqueoussodium hydroxide. The mean titre was 26.60 cm3 of aqueoussodium hydroxide.Calculate the value of x in Na2CO3.xH2O Show your working.Give your answer as an integer.[7 marks]

I have worked out the moles for HCl (0.05) and for NaOH (3.99x10^-2)

What do I do now lol


You have found the number of moles of HCl that would react with NaOH in 250cm3.
Find the number of moles of HCl that reacted with hydrated sodium carbonate in 250cm3
Find the number of moles of hydrated sodium carbonate in 250cm3
This contains 627 mg
So find the molar mass of hydrated sodium carbonate
Find the value of x to the nearest integer (1)
Reply 2
Avatar for Alifjfjf
Alifjfjf
3
Why do I divide by 2?
Original post by Alifjfjf
Why do I divide by 2?

due to the stoichiometric ratio in the balanced equation, you need to divide by 2 to find how much there is in one mole
You must hate the student that added 627 mg of hydrated sodium carbonate (Na2CO3.xH2O) to 200 cm3of 0.250 mol dm–3 hydrochloric acid in a beaker and stirred the mixture. Why did they have to make your life so difficult? Couldn't they have just figured it out themselves?
why do you times the NaOH moles by 10?
Original post by username5463
why do you times the NaOH moles by 10?

(3.99 x 10^-3) x (250/50)
Original post by username5463
why do you times the NaOH moles by 10?

you want the number of moles in 250cm3, we found 25cm3 of NaOH so x10 gives you moles in 250cm3
Reply 8
Avatar for zuhairt
zuhairt
2
can you please explain how that balanced equation is formed?
Reply 9
Avatar for zuhairt
zuhairt
2
Original post by username5461056
due to the stoichiometric ratio in the balanced equation, you need to divide by 2 to find how much there is in one mole

can you please explain how to get to that balanced equation?

Quick Reply

Related discussions

Latest

Trending

Trending

Articles for you