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Chemistry Forums for Students => High School Chemistry Forum => Topic started by: Shea on August 02, 2006, 09:25:00 PM

Title: Solutions?
Post by: Shea on August 02, 2006, 09:25:00 PM

How many moles of Ca(NO3)2 must be added to enough water to make 100mL of 2M Ca(NO3)2 solution?

How many grams of AgNO3 must be added to sufficient water to make a 200m L of 0.5M AgNO3 solution?

In these, do I just divide the 2M and the .5M by their respective amounts, and then convert those to their desired units?

Title: Re: Solutions?
Post by: Will on August 02, 2006, 09:31:44 PM

Quote from: Shea on August 02, 2006, 09:25:00 PM

How many moles of Ca(NO3)2 must be added to enough water to make 100mL of 2M Ca(NO3)2 solution?

How many grams of AgNO3 must be added to sufficient water to make a 200m L of 0.5M AgNO3 solution?

In these, do I just divide the 2M and the .5M by their respective amounts, and then convert those to their desired units?

No. You convert the ml to dm³ first and then multiply by the concentration. For the second one you will need to multiply the moles by the M_r to get the grams of AgNO₃. Hope that helps.

Title: Re: Solutions?
Post by: Shea on August 02, 2006, 09:49:47 PM

It helped, but first you gotta tell me what dm³, and M_r is...

Title: Re: Solutions?
Post by: Will on August 02, 2006, 09:54:41 PM

dm³ is decimetres cubed, which is the same thing as litres. To convert cm³(ml) into dm³(l) you just divide the value by 1000.

M_r is relative molecular mass.

Title: Re: Solutions?
Post by: Shea on August 02, 2006, 10:15:44 PM

Ok, I think I see what you're getting at...

BTW, do you know what the major salts are in sea water? Or what the chemical name is for Antifreeze?

And what is water hardness?

Title: Re: Solutions?
Post by: Will on August 02, 2006, 10:24:33 PM

Quote from: Shea on August 02, 2006, 10:15:44 PM

Ok, I think I see what you're getting at...

BTW, do you know what the major salts are in sea water? Or what the chemical name is for Antifreeze?

And what is water hardness?

Sea water (http://en.wikipedia.org/wiki/Sea_water) (See bottom right for list of ions)
Antifreeze (http://en.wikipedia.org/wiki/Antifreeze)
Water hardness (http://en.wikipedia.org/wiki/Water_hardness)

Sorry for appearing lazy; it is just that the answers could have easily been found using google.

Title: Re: Solutions?
Post by: Shea on August 02, 2006, 10:36:07 PM

Thanks.  Now, do you know what the common salts are in tap water?  Googling it didn't turn up much.

Title: Re: Solutions?
Post by: Will on August 02, 2006, 10:53:41 PM

Quote from: Shea on August 02, 2006, 10:36:07 PM

Thanks.  Now, do you know what the common salts are in tap water?  Googling it didn't turn up much.

I would imagine all the same ions as sea water will be there like sodium, potassium, calcium, magnesium, chloride and sulfate. But I would also expect higher concentrations of fluoride and much lower concentrations of ions like sodium and chloride. I wouldn't know what the 'common' ones are. There are also many other ions like other metal ions, carbonates etc. that are present in tap water. I am jet-lagged so I don't have time to go through google thoroughly.