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# confused !!!

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Find your uni forum to get talking to other applicants, existing students and your future course-mates 27-07-2015
1. Q. which of these metals has the least tendency to form positive ions ??
aluminium, calcium, iron, sodium and zinc??

Q.which of the following can be deduced from the equation below ?

2H2O2 ----- 2H2O + O2

(a) The volume of oxygen produced from 200cm3 of aqueous hydrogen peroxide is 100cm3.

(b) When completely decomposed, 17g of hydrogen peroxide form 9g of water and 8g of oxygen.

Q. a test tube contains a dilute solution of a solid X dissolved in liquid Y. I want to know that in order to measure the boiling point of liquid Y where should the thermometer be placed ... should the bulb be dipped in the liquid or should it be next to the outlet pipe above the liquid Y .
2. (Original post by e-n-i-g-m-a)
Q. which of these metals has the least tendency to form positive ions ??
aluminium, calcium, iron, sodium and zinc??

Q.which of the following can be deduced from the equation below ?

2H2O2 ----- 2H2O + O2

(a) The volume of oxygen produced from 200cm3 of aqueous hydrogen peroxide is 100cm3.

(b) When completely decomposed, 17g of hydrogen peroxide form 9g of water and 8g of oxygen.

Q. a test tube contains a dilute solution of a solid X dissolved in liquid Y. I want to know that in order to measure the boiling point of liquid Y where should the thermometer be placed ... should the bulb be dipped in the liquid or should it be next to the outlet pipe above the liquid Y .
For the first question, it's either Al because it forms 3+ or it's Zn... I think the one that is the least reactive probabily has the least tendency to lose electrons to become ions. So i think it's most likely to be Zn... not sure though

The second question, it's (a)
3. The thermometer should be placed just above the surface of the liquid so that it's not in the liquid but very close to it.
4. First question is to do with reactivity series - the higher the element is in the series the greater the tendency to oxidise. From greatest to least tendency in your list: sodium, calcium, aluminium, zinc, and iron.

(a) cannot be deduced: hydrogen peroxide is liquid. If both were gases it would be true. (b) is untrue, according to my calculations 4g of oxygen should be produced.

It should be as centrally in the liquid as possible - not touching the glass. When a liquid begins to boil its temperature does not increase, all energy is spent breaking bonds - so entire liquid should be same temperature for a while.

Oldak.

PS glance. Surely above the liquid you'd be measuring the temperature of both the air and the gas? The gas can also, of course, exceed the boiling point.
5. for question 2 why cant the answer be (a) .. i mean two moles of hydrogen peroxide are reacting to produce one mole of oxygen !!
6. Q1. The most likely to form positive ions is the most reactive, so look to the reactivity series. The LEAST likely to form +ve ions will be the LEAST reactive, so the answer's iron. I did have to look at a reactivity series for that though. Knowing me, i've got that exactly wrong

Agreed with revenge on Q2 - (a) Edit#2: THIS IS WRONG

Q3. The thermometer should be next to the outlet pipe. This is because the boiling point of a solution is not a clear value, but the vapour given off will be of one temperature.

Edit: Q1 is right - im sure now.

check out this website for revision on Q1 and related stuff - it's pretty good.

http://www.wpbschoolhouse.btinternet...Reactivity.htm
7. (Original post by e-n-i-g-m-a)
for question 2 why cant the answer be (a) .. i mean two moles of hydrogen peroxide are reacting to produce one mole of oxygen !!
The hydrogen peroxide is a liquid, and the oxygen is a gas.
8. Ah damn - apologies for my answer to Q2 - i was wrong
9. Hydrogen peroxide is a liquid at standard conditions. Therefore, because of n=c/v, to know the number of moles to work out the volume of oxygen gas produced, you would need to provide the concentration of H2O2.

Mole-volume proportionality could only be true if both oxygen gas and hydrogen peroxide had the same molar mass or if both were gases.

Oldak.
10. its okay ...at least i got the answers !!! thanks a lot !!!
Updated: June 2, 2005
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