chemistry unit 3 !!! discussion in here !! =p

[U stalking ME]

mm.. another question heat enthalpy per mol we should wr8 -ve or +ve thats it r8 ??
but when we calculate the total enthalpy no ?
or the opposite ? =$ =p !
thx again =p !

yes we have to rite the sign (ALWAYS) and first we calculate the total enthalpy, then heat enthalpy per mol.

 

[DANGERBP]

Decanting can be used to separate a liquid from an insoluble solid. As the solid settles to the bottom of the container, the liquid can be carefully poured into another container leaving the solid (sediment) behind. Decanting can also be used to separate two immiscible liquids like oil and vinegar.

Precipitation reactions: When an insoluble solid called a precipitate forms when reactants are formed together.
For example, when carbon Dioxide is mixed with Calcium Hydroxide (Limewater), The precipitate Calcium carbonate is formed.

haha thanks to infinity ! =p

 

[DANGERBP]

yes we have to rite the sign (ALWAYS) and first we calculate the total enthalpy, then heat enthalpy per mol.

no so we r8 it when we calcuculate per mol too ??

 

[U stalking ME]

no so we r8 it when we calcuculate per mol too ??

yea wen we calculate energy per mol not if we r only calculating no. of moles

 

[U stalking ME]

haha thanks to infinity ! =p

welcome to infinity!!

 

[DANGERBP]

http://www.thestudentroom.co.uk/wik...boratory_Techniques_-_Group_1_and_2_Reactions

thank you !

 

[¦HaLo¦]

thank you !

yw

 

[DANGERBP]

describe a procedure by which you prepare 250 cm^3 of an acid accurately of known concentration ! your provided with a weighted bottle containin bet 2.4 > 2.5 g of the acid ?
hows that ??

 

[DANGERBP]

yw

hey was wonderin wat does your avatar mean ? =p !

 

[xIshtar]

describe a procedure by which you prepare 250 cm^3 of an acid accurately of known concentration ! your provided with a weighted bottle containin bet 2.4 > 2.5 g of the acid ?
hows that ??

Thats making a standard solution I believe. You have to use a volumetric flask and such.

 

[DANGERBP]

Thats making a standard solution I believe. You have to use a volumetric flask and such.

well ya but theres like 5 mark for it !! like wat da fk ???

 

[¦HaLo¦]

hey was wonderin wat does your avatar mean ? =p !

did u read the description of my avatar? it says that "No man, this is Fifa, Counterstrike is over there

 

[DANGERBP]

did u read the description of my avatar? it says that "No man, this is Fifa, Counterstrike is over there

pahahhahahah ! lol =p ! like it =p

 

[U stalking ME]

describe a procedure by which you prepare 250 cm^3 of an acid accurately of known concentration ! your provided with a weighted bottle containin bet 2.4 > 2.5 g of the acid ?
hows that ??

How is a 250cm3 standard solution prepared?

• Make sure that the balance is clean and dry. Wipe it with a damp cloth.
• Place the weighing bottle on the pan and take the balance (i.e. re-zero it)
• Take the bottle off the balance and add solid to it. This ensures that no spillages fall on the pan.
• Take the balance of the weighing bottle + solid and find the balance of solid by subtraction.
• Replace on balance, and if the required amount is added, withdraw the mass.
• When you have the required amount, write its value down immediately.
• Wash out a 250cm3 volumetric flask three times using pure water.
• Transfer the solid to a 250cm3 volumetric flask using a funnel, and wash out the weighing bottle into the flask through the funnel using distilled water.
• Add about 100cm3 of distilled water to the flask.
• Stir the solution using a glass rod until all the solid visibly dissolves into a solution.
• Wash all remaining apparatus including the glass rod, funnel and transfer the rest of this to the flask.
• Make up to 250cm3 with distilled water so that the bottom of the meniscus just touches the 250cm3 mark.
• Attach a stopper to the flask.
• Shake the flask vigorously and/or invert the flask 5 or 6 times to create a solution with uniform concentration.
• Concentration of solution = mass of solid used/molar mass of solid x 1000/250 (units moldm-3)

 

[xIshtar]

How is a 250cm3 standard solution prepared?

• Make sure that the balance is clean and dry. Wipe it with a damp cloth.
• Place the weighing bottle on the pan and take the balance (i.e. re-zero it)
• Take the bottle off the balance and add solid to it. This ensures that no spillages fall on the pan.
• Take the balance of the weighing bottle + solid and find the balance of solid by subtraction.
• Replace on balance, and if the required amount is added, withdraw the mass.
• When you have the required amount, write its value down immediately.
• Wash out a 250cm3 volumetric flask three times using pure water.
• Transfer the solid to a 250cm3 volumetric flask using a funnel, and wash out the weighing bottle into the flask through the funnel using distilled water.
• Add about 100cm3 of distilled water to the flask.
• Stir the solution using a glass rod until all the solid visibly dissolves into a solution.
• Wash all remaining apparatus including the glass rod, funnel and transfer the rest of this to the flask.
• Make up to 250cm3 with distilled water so that the bottom of the meniscus just touches the 250cm3 mark.
• Attach a stopper to the flask.
• Shake the flask vigorously and/or invert the flask 5 or 6 times to create a solution with uniform concentration.
• Concentration of solution = mass of solid used/molar mass of solid x 1000/250 (units moldm-3)

I agree completely, and I almost wrote all that out myself
But I thought that you should shake just before you make it up to the mark, as when you dissolve it in the solvent, can't it cause changes in volume which would then lead to inaccuracies?

 

[tripleA95]

What happens when you add potassium per manganate to an alkene?

 

[¦HaLo¦]

What happens when you add potassium per manganate to an alkene?

purple to colourless

 

[xIshtar]

What happens when you add potassium per manganate to an alkene?

That depends if it is acidified or not. If it slightly acidified it will go from purple to colourless as oxidation takes place.
But if it is slightly alkaline it will go from purple to a browny colour.

 

[DANGERBP]

How is a 250cm3 standard solution prepared?

• Make sure that the balance is clean and dry. Wipe it with a damp cloth.
• Place the weighing bottle on the pan and take the balance (i.e. re-zero it)
• Take the bottle off the balance and add solid to it. This ensures that no spillages fall on the pan.
• Take the balance of the weighing bottle + solid and find the balance of solid by subtraction.
• Replace on balance, and if the required amount is added, withdraw the mass.
• When you have the required amount, write its value down immediately.
• Wash out a 250cm3 volumetric flask three times using pure water.
• Transfer the solid to a 250cm3 volumetric flask using a funnel, and wash out the weighing bottle into the flask through the funnel using distilled water.
• Add about 100cm3 of distilled water to the flask.
• Stir the solution using a glass rod until all the solid visibly dissolves into a solution.
• Wash all remaining apparatus including the glass rod, funnel and transfer the rest of this to the flask.
• Make up to 250cm3 with distilled water so that the bottom of the meniscus just touches the 250cm3 mark.
• Attach a stopper to the flask.
• Shake the flask vigorously and/or invert the flask 5 or 6 times to create a solution with uniform concentration.
• Concentration of solution = mass of solid used/molar mass of solid x 1000/250 (units moldm-3)

thnk you so much ! but hey how did you know(( Add about 100cm3 of distilled water to the flask.)) that its 100 ??

 

[U stalking ME]

thnk you so much ! but hey how did you know(( Add about 100cm3 of distilled water to the flask.)) that its 100 ??

welcome and idk myself, it was written in the book :/ srry