Maths problem

[Hurin thalion]

Calculate ppt (parts per thousand), molarity (mol/L) and osmolarity (mOsm/L) of a salt solution prepped with 14.61g NaCl in .5L water.

Could someone please help me with this, I am needing to understand how to calculate things like this in preparation for exams soon. I cannot afford a tutor, so any support would be much appreciated, thanks for taking the time to read this post

[exchemist]

39 minutes ago, Hurin thalion said:

Calculate ppt (parts per thousand), molarity (mol/L) and osmolarity (mOsm/L) of a salt solution prepped with 14.61g NaCl in .5L water.

Could someone please help me with this, I am needing to understand how to calculate things like this in preparation for exams soon. I cannot afford a tutor, so any support would be much appreciated, thanks for taking the time to read this post

OK this really a chemistry problem, rather than a maths problem.

There are 3 things here. Let's take the easy one first. What do you think parts per thousand means and how would you set about calculating it?

For the second, you need to know the molar mass (in the old days called the "molecular weight") of NaCl. How do you find that out and what is it?

And then we can come back to the third.

Edited March 14, 2022 by exchemist

[Hurin thalion]

44 minutes ago, exchemist said:

OK this really a chemistry problem, rather than a maths problem.

There are 3 things here. Let's take the easy one first. What do you think parts per thousand means and how would you set about calculating it?

For the second, you need to know the molar mass (in the old days called the "molecular weight") of NaCl. How do you find that out and what is it?

And then we can come back to the third.

I believe that 1 ppt = 1g of NaCl in 1L of water? And as for molarity, am I taking the molecular weight of NaCl (58.44g/mol) and doing something with it which I fail to remember? :'D

[exchemist]

47 minutes ago, Hurin thalion said:

I believe that 1 ppt = 1g of NaCl in 1L of water? And as for molarity, am I taking the molecular weight of NaCl (58.44g/mol) and doing something with it which I fail to remember? :'D

Yes 1 litre has a mass of 1kg, right? Which means 1000 grammes. So 1 g of anything dissolved in 1 l must be 1 part in one thousand i.e. 1ppt. So now you can do the first bit, can't you? 

Next, the molecular weight, or molar mass,  is the mass of 1 mole of substance. So in the case of NaCL, if you have 58.44g of it, you have 1 mole. So how many moles, or rather, how much of a mole, would there be in 14.61g?   

P.S. it is now 22:22 in London and I am going to bed because I've got covid and want to get plenty of sleep (I'm fully vaccinated so it's just a nuisance). If you still need help in the morning I'll have a look after breakfast. I remember my son used to get in a flap with things like this. He could do them perfectly well really, but he used to panic. The thing to do is think calmly about each piece separately, and take it in steps.

 

Edited March 14, 2022 by exchemist

[studiot]

It is worth noting and remembering the difference between two derived quantities that sound almost the same.

molarity and molality

Quote

Molarity is the ratio of the moles of a solute to the total liters of a solution. The solution includes both the solute and the solvent. Molality, on the other hand, is the ratio of the moles of a solute to the kilograms of a solvent.

https://www.technologynetworks.com/analysis/articles/molarity-vs-molality-formula-and-definitions-334119

 

1 hour ago, Hurin thalion said:

I believe that 1 ppt = 1g of NaCl in 1L of water?

Not quite.

1 part per thousand of solution.

So 1 g salt in 999 g water.

Since the solution is very dilute the difference is small, but still important.

Osmolarity is different again

Quote

Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles of solute per litre of solution. The osmolarity of a solution is usually expressed as Osm/L, in the same way that the... Wikipedia

Edit

1 hour ago, exchemist said:

P.S. it is now 22:22 in London and I am going to bed because I've got covid and want to get plenty of sleep (I'm fully vaccinated so it's just a nuisance).

Sleep well and I hope it resolves soon, without any serious effects.

Edited March 14, 2022 by studiot

[exchemist]

11 hours ago, studiot said:

 

Sleep well and I hope it resolves soon, without any serious effects.

Thanks for the good wishes. It's just a runny nose, really. (But then I have had 3 doses of vaccine, plus an encounter with the original virus in March 2020.)  

[Hurin thalion]

On 3/14/2022 at 9:55 PM, exchemist said:

Yes 1 litre has a mass of 1kg, right? Which means 1000 grammes. So 1 g of anything dissolved in 1 l must be 1 part in one thousand i.e. 1ppt. So now you can do the first bit, can't you? 

Next, the molecular weight, or molar mass,  is the mass of 1 mole of substance. So in the case of NaCL, if you have 58.44g of it, you have 1 mole. So how many moles, or rather, how much of a mole, would there be in 14.61g?   

P.S. it is now 22:22 in London and I am going to bed because I've got covid and want to get plenty of sleep (I'm fully vaccinated so it's just a nuisance). If you still need help in the morning I'll have a look after breakfast. I remember my son used to get in a flap with things like this. He could do them perfectly well really, but he used to panic. The thing to do is think calmly about each piece separately, and take it in steps.

 

Hey apologies for the delay in responding, been snowed under with work :') I am also in the UK, I hope you get better soon! I am now going to go over it and I'll let you know how it goes

[exchemist]

49 minutes ago, Hurin thalion said:

Hey apologies for the delay in responding, been snowed under with work :') I am also in the UK, I hope you get better soon! I am now going to go over it and I'll let you know how it goes

Thanks, I'm feeling a bit better already. By all means come back here if you are still stuck. 

[Jakerm1995]

20 hours ago, exchemist said:

Thanks, I'm feeling a bit better already. By all means come back here if you are still stuck. 

Apologies it seems that the moderators banned my other account because I had more than one account. I just totally forgot about this one :'D But I can respond via this account now. Thanks again for your help on this and the other post, I'll update you as I go