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Chem 1 AQA Question Help!

Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and hydrochloric acid. The equation for the reaction is:


ZnO + 2HCl ---> ZnCl2 + H2O

A 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm^–3 hydrochloric acid.

The mark scheme works out the number of moles from the volume and concentration of HCl whereas I used the number of moles of Zinc Oxide to save time. This produces a different answer to the mark scheme, can somebody please tell me why they used these values to work out the number of moles rather than using the Zinc Oxide moles straight off.
Reply 1
Avatar for hedja
hedja
It depends which of the two was in excess, if there are less moles of HCl then not all the zinc oxide will be reacted, so it would be the HCl moles you need to use
Original post by Jaystreet
Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and hydrochloric acid. The equation for the reaction is:


ZnO + 2HCl ---> ZnCl2 + H2O

A 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm^–3 hydrochloric acid.

The mark scheme works out the number of moles from the volume and concentration of HCl whereas I used the number of moles of Zinc Oxide to save time. This produces a different answer to the mark scheme, can somebody please tell me why they used these values to work out the number of moles rather than using the Zinc Oxide moles straight off.


The whole question asks for the maximum mass of zinc chloride, the moles of HCl are in excess, therefore to get the maximum mass you use the HCl moles calculated by the data given.
Reply 3
Avatar for hedja
hedja
Original post by randlemcmurphy
The whole question asks for the maximum mass of zinc chloride, the moles of HCl are in excess, therefore to get the maximum mass you use the HCl moles calculated by the data given.


The HCl isn't in excess? there is 0.12 moles of HCl, but 0.083 of ZnO, with a ratio of 2:1 this means only 0.06 moles of ZnO reacted.
Reply 4
Avatar for abdulahi
abdulahi
6
Original post by Jaystreet
Zinc chloride can be prepared in the laboratory by the reaction between zinc oxide and hydrochloric acid. The equation for the reaction is:


ZnO + 2HCl ---> ZnCl2 + H2O

A 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm^–3 hydrochloric acid.

The mark scheme works out the number of moles from the volume and concentration of HCl whereas I used the number of moles of Zinc Oxide to save time. This produces a different answer to the mark scheme, can somebody please tell me why they used these values to work out the number of moles rather than using the Zinc Oxide moles straight off.



Original post by hedja
It depends which of the two was in excess, if there are less moles of HCl then not all the zinc oxide will be reacted, so it would be the HCl moles you need to use



Original post by randlemcmurphy
The whole question asks for the maximum mass of zinc chloride, the moles of HCl are in excess, therefore to get the maximum mass you use the HCl moles calculated by the data given.



ok basically im not sure but they said "A 0.0830 mol sample of pure zinc oxide was added to 100 cm3 of 1.20 mol dm^–3 hydrochloric acid"

and they want the moles of HCL

they did not say they reacted them together so you cannot use the moles of ZnO to find out the moles of HCL, they just ADDED them



you could use your method if they said "A 0.0830 mol sample of pure zinc oxide REACTED with 100 cm3 of 1.20 mol dm^–3 hydrochloric acid"
Reply 5
Avatar for duakua
duakua
hey could some one please help with thiis question
3NO2+H2O= 2HNO3 +NO
calculate the concentration of nitric acid produced when 0.543 mol of NO2 is reacted with water and the solution is made up to 250cm3

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