preparing solutions...help???

Question

Could you please explain to me how you do these? What are the steps to do these? I really just need a walk through and how to get started...thank you much

How would you make 200 ml 2.5X buffer starting with a 50X stock?


How would you prepare 100 ml of 150 mM Tris buffer (pH 8.0)? The molecular weight of Tris is 121.1 g/mole.


How would you prepare a 1% (w/v) NaNO3 solution?

Answer 1

For dilutions always use the equation
C1*V1=C2*V2
As long as C1,C2 are expressed in the same units and V1,V2 in the same units we don't care what units they are. e.g. C could be mg/ml, g/ml, %, even number of hippos per bus.

50*V1=200*2.5 => V1=10 ml of stock. Put 10 ml of stock in an appropriate volumetric cylinder, add water to 200 ml and mix.

b) mole=C*V
mole=mass/MW
So mass/MW=C*V Now we have to express C in mole/L and V in L
mass=C*V*MW= 0.150*0.1*121.1= 1.8165 g

Add this amount of Tris in a 100ml volumetric cylinder containing approximately 90 ml of water. Once it has dissolved, add dropwise HCl, while stirring and monitoring the pH with a pH-meter until you reach pH=8.00
Then add water up to 100 ml, mix and you're done

1% (w/v) means 1 g per 100 ml solution How much do you want to prepare? If you want 100ml then just dissolve 1 g NaNO3 in some water (in a volumetric flask or cylinder) and then add water up to 100 ml.

Answer 2

1. you use the equation V1C1=V2C2. i will replace X for N (normality).
200ml 2.5 N = 50 N (x)
10ml = x
so you need 10ml of 50 N, and fill up to 200ml.


2. (121.1g/mol) x (0.150 mol/1) x (1/100ml) = 0.18165g/ml
weigh 0.18165g in 100 ml of water.

3. you just need to weigh 1g of NaNO3 into 100 ml of water.

Answer 3

very confusing issue. seek over google or bing. just that can help!