Finding the concentration in a solution

[morgan8222]

I am doing a lab to find the concentration of copper in a penny. I am confused on how to find the concentration of copper in each solution I prepared. One solution for example:

2 ml of 0.080 M Cu(NO3)2
add 2 ml of concentrated ammonium hydroxide
dilute solution to 50 ml

Can someone help me out?

 

[sjb-2812]

I am doing a lab to find the concentration of copper in a penny. I am confused on how to find the concentration of copper in each solution I prepared. One solution for example:

2 ml of 0.080 M Cu(NO3)2
add 2 ml of concentrated ammonium hydroxide
dilute solution to 50 ml

Can someone help me out?

What is the definition of concentration?

 

[CrimpJiggler]

I'm confused. You have to find the concentration of copper in a penny. What has this got to do with adding 2 mL of NH₄OH to Cu(NO₃)₂? Anyhow, you want to know how to find the concentration of copper in that 54 mL solution you prepared. Firstly, figure out how much copper is in 2 mL of 0.08M copper nitrate solution. M means moles per liter. This means there are 0.08 moles of copper nitrate in a liter of that solution. You only have 2 mL so how many moles are in that?

 

[sjb-2812]

I'm confused. You have to find the concentration of copper in a penny. What has this got to do with adding 2 mL of NH₄OH to Cu(NO₃)₂? Anyhow, you want to know how to find the concentration of copper in that 54 mL solution you prepared. Firstly, figure out how much copper is in 2 mL of 0.08M copper nitrate solution. M means moles per liter. This means there are 0.08 moles of copper nitrate in a liter of that solution. You only have 2 mL so how many moles are in that?

What 54 ml solution?

 

[Borek]

Concentration of copper, or of tetraamminediaquacopper(II)? Or total copper in any form?

 

[morgan8222]

It is a total of 50 ml. Water is added to the solution until it is 50 ml.
0.080 M Cu(NO3)2 = 0.00016 moles in 2 ml

 

[morgan8222]

"Total concentration of copper" in this solution I prepared.

 

[sjb-2812]

It is a total of 50 ml. Water is added to the solution until it is 50 ml.
0.080 M Cu(NO3)2 = 0.00016 moles in 2 ml

Is there any other source of copper?

 

[Borek]

"Total concentration of copper" in this solution I prepared.

Then it is simple dilution. Number of moles of copper doesn't change, it is constant - just the volume changes.

Note: it looks messy, as these are two cross posted threads merged.

 

[chikis]

What is the definition of concentration?

Concentration can be defined as the measure of amount of substance dissolved in known volume of a given solution. It is expressed in (amount in grammes of the substance per cubic centimete of solution when the mass concentration is concerned) gcm-3. It can also be expressed as in (amount in mole of substance per cubic decimeter of solution if the molar concentration is required ) moldm-3.
I can infer from this defination that it is not easy to determine the concentration of a substance say copper in a penny unless the copper is disolved in a given volume of a solution. Your views are welcome. Thank you.

 

[Borek]

Concentration can be defined as the measure of amount of substance dissolved in known volume of a given solution.

Not bad, but not perfectly OK as well. Concentration can be also expressed as mass per mass (say 10% w/w NaCl solution means in each 100 g of solution there is 10 g of NaCl - whatever the volume is). It can be also expressed in terms of molar fraction, moles per mass of solvent (it is known as molality then) and so on.

I can infer from this defination that it is not easy to determine the concentration of a substance say copper in a penny unless the copper is disolved in a given volume of a solution. Your views are welcome. Thank you.

See above. There are other ways of expressing concentration that will be perfectly suitable to copper in penny. Mass per mass percentage would be my choice.

 

[chikis]

Not bad, but not perfectly OK as well. Concentration can be also expressed as mass per mass (say 10% w/w NaCl solution means in each 100 g of solution there is 10 g of NaCl - whatever the volume is). It can be also expressed in terms of molar fraction, moles per mass of solvent (it is known as molality then) and so on.
You have sold me again! What does that w/w denote?

See above. There are other ways of expressing concentration that will be perfectly suitable to copper in penny. Mass per mass percentage would be my choice.

But like what I just said if any person want to determine the concentration of copper in a penny; at least that person have to dissolve that penny in a solution before it will be easy to find the concentration of copper in it. How about that?

 

[Borek]

But like what I just said if any person want to determine the concentration of copper in a penny; at least that person have to dissolve that penny in a solution before it will be easy to find the concentration of copper in it. How about that?

You mean for analysis? Yes - and no. If the coin has identical composition in all its volume, there are methods (I am not sure about English name - something like spark spectroscopy, spark atomic emission spectroscopy) that can be used to analyze composition just by locally heating the surface with electric arc. But the simplest approach is to dissolve the sample and use some wet method like titration, such an approach doesn't require any costly hardware.

 

[chikis]

Not bad, but not perfectly OK as well. Concentration can be also expressed as mass per mass (say 10% w/w NaCl solution means in each 100 g of solution there is 10 g of NaCl - whatever the volume is). It can be also expressed in terms of molar fraction, moles per mass of solvent (it is known as molality then) and so on.
You have sold me again! What does that w/w denote? You have not answered my question on yet. Please tell me what that w/w mean so that I will be following. Alright!

 

[Borek]

w/w = weight/weight or mass percentage

v/v = volume/volume or volume percentage

See concentration lectures for more details.