[mass]

I am trying to do a past exam paper for chemistry, except theres no mark scheme for it and I can't even do 90% of the questions. I need help with any of them. Please help me.

[AWK]

Hint for 1a
How do you call reaction of acid with base?
How do you cal reaction with electrons moving between reagents?
Sometimes titration can be also called after reagent used, eg manganometry, iodometry.

Hint for 3
What Huckel rule says? Can you count nonbonded electrons up to 6?

[mass]

Hint for 1a
How do you call reaction of acid with base?
How do you cal reaction with electrons moving between reagents?
Sometimes titration can be also called after reagent used, eg manganometry, iodometry.

Hint for 3
What Huckel rule says? Can you count nonbonded electrons up to 6?

I forgot to mention I actually managed both these questions.
1a . reduction titration
3. Huckels rule is 4n+2, planar, conjugate and an uninterrupted ring of pi electrons with an odd number of electrons.

[mass]

come on guys help me, I am really depressed

[Borek]

When there is reduction, there is also oxidation, that's why these reactions are called redox.

You are given balanced reaction equation, it is simple stoichiometry. How many moles of cerium were used? Which means how many moles of ascorbic acid in sample? Convert these moles to mass - and you are ready to calculate %.

[mass]

question 2?

[sjb]

Are http://en.wikipedia.org/w/index.php?title=Back_titration&oldid=183339659, and http://www.biodieselcommunity.org/turmeric/ of any use?

S

[mass]

Given solution A (SG 1.10) and solution B (SG 1.25) what volumes of A and B would give 200ml of  SG 1.20 when mixed together?

Volume of A to nearest ml      Volume of B to nearest ml

a)   100            110
b)   133            125
c)   67               133   
d)   110            67
e)   125            100

[Borek]

Given solution A (SG 1.10) and solution B (SG 1.25) what volumes of A and B would give 200ml of  SG 1.20 when mixed together?

Volume of A to nearest ml      Volume of B to nearest ml

a)   100            110
b)   133            125
c)   67               133   
d)   110            67
e)   125            100

This is the most stupid question I have ever seen. Volumes are not additive, so there is no correct answer. Most likely they want you to assume volumes ARE additive; they can want you to assume that gravitation is a repulsive force as well.

[mass]

why can't two volumes be additive though?

[Borek]

Because solutions are not ideal. If you mix 100 mL of water with 100 mL of ethanol you get 193 mL of mixture. When you mix 100 mL of water with 100 mL of sulfuric acid you get 183 mL.

Take a look at attached pictures - these are two cases where solutions of given densities are mixed to obtain 200 mL of the 1.2 g/mL solution. Each answer is different, neither is listed as a choice.

[mass]

So we will have to take it that they assume no loss occurs during mixing right? there must be a way to work it out borek. It's not a strict chemistry question, its actually relating to pharmacy but with the involvement of concentrations I thought I would ask here.

[Borek]

there must be a way to work it out borek.

Yes, there is. It is based on assumption that volumes are additive. As I have shown you this assumption is wrong. Whoever asked this question should learn a few things about solutions.

[AWK]

Given solution A (SG 1.10) and solution B (SG 1.25) what volumes of A and B would give 200ml of  SG 1.20 when mixed together?

Volume of A to nearest ml      Volume of B to nearest ml

a)   100            110
b)   133            125
c)   67               133   
d)   110            67
e)   125            100

As Borek pointed out this problem can be solved only assuming additivity of volumes which is not a case even for relativelz diluted strong acids, bit can be quite safelz used for diluted organic compounds in water solution. Unfortunately, then density of solution rather do not exceed 1.05

Assuming additivity of volumes d1V1+d2V2=d3(V1+V2).
In this case only one solution fulfills requirements. I estimate other possibilities show errors exceeded 20%.

[mass]

Tbh I dont care about the assumptions, I need the answer so I can work out how to do it. Can you provide me with that please as it's extremely difficult for me to get anywhere without a mark scheme and hence I posted on here.