Just some help on a few simple short questions:

[latkan]

I need some help with these how would you apporach them to answer it any hints:

 

1) whether two solvents will mix or which will sit on the top?

 

2) how to prepare molar solutions?

 

3) finding errors in transcribing results?

 

4) what are serial and non-serial dilution and what they are used for?

 

Pls help thx

[Psycho]

2) how to prepare molar solutions?

For that you need to get the chemical in question, work out its mass, divide that by its atomic weight to find the amount of moles then dissolve that in a know amount of deionised water to make the solution.

4) what are serial and non-serial dilution and what they are used for?

Serial dilutions are just diluting a solution repeatedly by the same factor.

 

It can be used before plating bacteria, so you would make serial dilutions and then plate them out on agar and one will give you a plate with a viewable amount of bacteria (not to many not to little) so you can see what it contains, you can then scale this amount up again to find out how much is in the solution and what species they are.

[thedarkshade]

For that you need to get the chemical in question, work out its mass, divide that by its atomic weight to find the amount of moles then dissolve that in a know amount of deionised water to make the solution.

Something like that!

 

Suppose you have 100g of NaCl. First you calculate how moles of NaCl are there.

 

[math]n=\frac{m}{M}=\frac{100g}{58.44\frac{g}{mol}}=1.71 mol[/math]

 

so there you got the moles.

 

Now suppose you want to dissolve them into 500ml of water, and want to now the concentration of the solution. At school we use this formula:

 

[math]c=\frac{n}{V}[/math] put the data in the equation and you get what you need in this example.

 

[math]c=\frac{n}{V}=\frac{1.71mol}{0.5dm^3}=3.42\frac{mol}{dm^3}[/math]