Chemistry Calculation Question

Looks a lot like a homework question. Have you made a start on it, or just want someone to do your homework for you?

Not homework thankfully! Im 20 years out of college and I didnt study chemistry at high school or college which is the problem and why im here. Im happy to calculate the thing myself if someone can give me pointers.

I have made a start to it but no idea if im right or even headed in the right direction.

My understanding based on some internet searching is that I need to know the 'Molar Mass' of each compound first, and then the 'Atomic Weight' of each element.

So for Sodium bicarbonate I have Mol Mass = 84.0066g;
and the Atomic Weight is 22.99

To find out how much Sodium is in 1g, i'm dividing 22.99 by 84.0066 and multiplying the answer by 1 which equals 0.274g/g, or 274mgs per 1000mgs.
The amount of Sodium in the 5g mixture is 620mgs which by my calculations equals 2.26g (2260mgs) of Sodium bicarbonate per 5g, multiplied by 200 (to get the 1000g amount) = 452g of Sodium bicarbonate per 1000g. Am I close?

I did Magnesium Chloride hexahydrate calculation too.
Molar mass: 203.31
Atomic weight of Magnesium: 24.305

Then, 24.305 divided by 203.31 multiplied by 1 = 0.12g/g, or 120mgs per 1000mgs. The amount of Magnesium in the 5g mixture is 20mgs which works out to be around 0.17g (170mgs) of Magnesium chloride per 5g, times 200 = 34g per 1000g.

If those two are correct or close I can work the other two remaining compounds myself obviously. Just need someone to check the Math and steer me in the right direction.

Thanks.

15 years ago I would have been all over it. But I’d have to re-learn this stuff, and no longer have the time

Unless I'm missing something, this isn't chemistry, it's just straightforward math. If you have 32mg of Ca in a 5 gm sample, you have 32mg/5gm*450gm = 2880mg or 2.88gm in he 450gm sample. You can do the same ratio for all the other components.

I'm not sure the Math adds up with that approach.

Taking the other 3 compounds with your method you would get:

Sodium bicarb: 620mg/5g*450g = 55.8g
Potassium bicarb: 814mg/5g*450g = 73.26g
Mag. chloride: 20mg/5g*450g= 1.8g

That totals 130.86g + your Ca value of 2.88g gives you at total of 133.74g which is way off 450g. What is the remaining 316.26g?

I think you have to factor in the chemistry, and specifically the molar mass of each compound and then the atomic weight of each element because they are all chemical compounds rather than simply individual chemical elements.

The math doesn't add it in your initial sample either. If you add .032, 0.02, .620 and .814, you don't get 5gm. Either there is filler in the original mixture or you are missing information. The only reason you need to know the molar mass is if you are analyzing a reaction.

Suppose I give you a box full of balls of all different sizes and colors. I tell you the box weighs 10kg and the red balls in the box make up 1kg. I give you a second, identical box and ask you what weight of red balls you have now. You're going to say 2kg. You don't need to know the size of the red balls, the weight of each individual ball or anything about the other balls to answer the question.

But take Sodium bicarbonate. That is a compound that contains 274mgs of Sodium per 1000g, the rest is 'bicarbonate'. To calculate that figure you need to know the molar mass of Sodium bicarbonate which is 84.0066g and Sodium's atomic weight which is 22.99. Then you get 22.99 / 84.0066 * 1g = 274mgs Sodium. The rest of the 1g (726mgs) is the bicarbonate, no?

How does your method account for the bicarbonate? Or put another way, how would you calculate how much sodium is in 1g of sodium bicarbonate?

I see the issue now. Sorry, I misread your question and you are correct, you need the mass. To find the total weight, take the weight of the element given in the question, divide by the atomic mass of the element and multiply be the atomic weight of the compound.

So for NaHCO₃, you have 0.62 gm of Sodium at a weight of 23, so 0.62/23*84 = 2.26 gm of NaHCO₃. Scaling up to 450gm, you would use 2.26/5*450 = 203.8gm.