Molar Solutions

[paulsutton]

I want to make a solution of Citric Acid, for experiments,   so just asking here to make sure my method is correct

So to make 250ml of 1M Citric Acid and having looked up the Molecular weight of Citric Acid:

I need to  calculate as follows

Producing 250ml – so need to weigh out ¼ of the molar mass

• 192.12g / 4 = 48.03g which is the same as
• 0.25 (ml) x 192.12g

Where 192,12 is the mass of Citric Acid  therefore 1 Mol

As i Mol is  Formula Weight in 1 Litre of water,  then we only need 1/2 of this as 250 ml is 1/2 of litre

Therefore just dissolve 48.03 g in 250ml water.

As I don't have a lab balance,  Will use 48g,

This is for home Chemistry anyway.

 

Just checking, 

Thanks

Paul

[exchemist]

11 minutes ago, paulsutton said:

I want to make a solution of Citric Acid, for experiments,   so just asking here to make sure my method is correct

So to make 250ml of 1M Citric Acid and having looked up the Molecular weight of Citric Acid:

I need to  calculate as follows

Producing 250ml – so need to weigh out ¼ of the molar mass

• 192.12g / 4 = 48.03g which is the same as
• 0.25 (ml) x 192.12g

Where 192,12 is the mass of Citric Acid  therefore 1 Mol

As i Mol is  Formula Weight in 1 Litre of water,  then we only need 1/2 of this as 250 ml is 1/2 of litre

Therefore just dissolve 48.03 g in 250ml water.

As I don't have a lab balance,  Will use 48g,

This is for home Chemistry anyway.

 

Just checking, 

Thanks

Paul

Yes I mole weighs 192g, so 192g dissolved in 1litre would be a 1 mol solution. So for 250ml you need a quarter of the amount.

Not sure where your 1/2 comes in - typo? (250ml is 1/4 of a litre of course, as you correctly imply in your calculation.)  

[paulsutton]

1 minute ago, exchemist said:

Yes I mole weighs 192g, so 192g dissolved in 1litre would be a 1 mol solution. So for 250ml you need a quarter of the amount.

Not sure where your 1/2 comes in - typo? (250ml is 1/4 of a litre of course, as you correctly imply in your calculation.)  

Good point,  thanks

 

[paulsutton]

So another question here,  which may help others too, is do I really need 1 Mol concentration for simple experiments,

If I wanted to make 0.5 mol but the same amount 250ml, I guess would use

24g as that is 1/2 of what is needed for 1 mol

 

 

 

 

[exchemist]

39 minutes ago, paulsutton said:

So another question here,  which may help others too, is do I really need 1 Mol concentration for simple experiments,

If I wanted to make 0.5 mol but the same amount 250ml, I guess would use

24g as that is 1/2 of what is needed for 1 mol

 

 

 

 

There's nothing magic about using 1 molar solution. Sure, 0.5 M would need half the mass in the same volume of solvent.

But as far as strength of the acidity goes, if you are using a weak acid the actual acidity of the solution you make, i.e. the concentration of H+, will not be linear with concentration of the acid you add, since dissociation is only partial. It will take place to a greater degree, as a proportion of the acid added, in a more dilute solution, because the equilibrium HA <-> A⁻ + H⁺ will lie further to the right at low  concentrations of H⁺ and A⁻ .