Unit 4 Questions MEGATHREAD!

[Vincezor]

How do?
(Image removed from quote.)

You look up bromophenol blue Ka value in your data booklet (6*10^-5) and then you know the ratio of [HIn]/[In-] is 100/1 so you sub that in

Find and use to find the pH

IIRC it should be 2.22 or something

[DisaFear]

Why is electrolysing a dilute aqueous solution of sodium chloride a more efficient way to produce hydrogen than electrolysing water?

[david10d]

how does diluting a reaction change its equilibrium?

[BoredSatan]

how does diluting a reaction change its equilibrium?

increases the volume.. which favours side with more mols

[DisaFear]

Why is electrolysing a dilute aqueous solution of sodium chloride a more efficient way to produce hydrogen than electrolysing water?

Bump, anyone?

Also

State three distinct properties which are desirable in the electrodes using in fuel cells

[Panicmode]

Why is electrolysing a dilute aqueous solution of sodium chloride a more efficient way to produce hydrogen than electrolysing water?

Bump, anyone?

Also

State three distinct properties which are desirable in the electrodes using in fuel cells

It's cheaper? (Sea water is less expensive than fresh water)

3 distinct properties:

- Must conduct electricity
- Must be porous to allow contact between gases (so that gases and electrolyte can come in contact)
- Would be useful if they acted as catalysts

[DisaFear]

It's cheaper? (Sea water is less expensive than fresh water)

Though, I don't see what being cheaper has to do with efficiency. Someone I asked said 'greater ion population', ring any bells?

[Panicmode]

It's cheaper? (Sea water is less expensive than fresh water)

Though, I don't see what being cheaper has to do with efficiency. Someone I asked said 'greater ion population', ring any bells?

Ahh, googled it and figured out why

Pure water is a very poor conductor (duh!) so adding ions allows electricity to be conducted more effectively and allows electrolysis to be more efficient.

[Mao]

Higher conductivity.

Think back to galvanic cell, if your salt bridge is dry, then there's no reaction.

Now back to electrolytic cells. There's no real 'salt bridge' in this setup, but something has to fulfil this function (i.e. ions move from one electrode to the other to complement/counterbalance the electron flow). Pure water is a poor conductor (not much ions in there, poor ion mobility, :. not many ions go from one electrode to the other), thus the total current is very low, thus the rate of reaction is also slow.

Using a salt solution (more conductive, more ion mobility), the current can be much higher. Thus a higher rate of reaction.

[DisaFear]

Friend asks in relaliation to that:

But pure water has h3o+ and oh- ions, which would allow it to conduct electricity wouldn't it?

[Panicmode]

Friend asks in relaliation to that:

But pure water has h3o+ and oh- ions, which would allow it to conduct electricity wouldn't it?

Yes, it has them in concentrations of 10^-7

Not exactly high...

[david10d]

can we get a check up witht his question

Question 3
Which of the following changes will always ensure an increase in the rate of a chemical
reaction?
I Adding a catalyst
II Increasing temperature
III Increasing concentration
IV Increasing the surface area of the reactant

[HarveyD]

why can we assume that [H30] = [H-] for weak acids?

[Asx4Life]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

[DisaFear]

How come increasing the surface area of reactants wont increase the rate of a chemical reaction?

Where'd you get this from?