# Need Help with Chemistry!

Just answer me thinking that I don't know anything.

I have a few problems.

1. How do I know how many ions does a compound break into by just looking at the chemical formula of the compound?

2. If two compounds are mixed, how do I know which ions will combine and precipitate?

3. Most importantly, if the chemical formula is written in text, how do I know how many atoms of each element are present. For e.g. if Copper (II) Chloride is written, how do I figure out that it is CuCl?

## Answers and Replies

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3.Cooper(II) Chloride is CuCl2

It s already written Copper(II), that means you have copper with oxidation number +2
Chlorine element is HALOGEN, the same like eg. fluorine, bromine, iodine. They all have oxidation number -1.
Now when you know oxidation number of both elements, you just easily exchange them and all what you have to do its to write them behind their neighbour element.
Oxidation number + 2 from copper you write behind chlorine and oxidation number -1 from chlorine you write behind copper ( if the oxidation number is one you don`t have to write it ).Then you look at formula CuCl2 and you will see that there is 1 copper atom and 2 chlorine atoms.

OK, thanks,

what about the other questions

2. If two compounds are mixed, how do I know which ions will combine and precipitate?

Solubility table and I believe it's table 4.1 in Brown, LeMay and Bursten, The Central Science 10th edition.
Most of the time : AB + CD --> AD + BC . I usually use exchange method and see any precipitation.

i need help!

Questions:

1. Calculate the volume of carbon dioxide at 273 K and 1.01 * 10^5 Pa which would be produced when 1.25g of calcium carbonate reacts completely with HCL.

and

2. When 41.18 cm^3 of a solution of silver ions with concentration of .2040 mol dm^-3 is added to a solution of XO4 -3 ions 1.172g of precipitate are formed.
i) calculate the amount in moles of Ag+ used in the reaction.
ii)Calculate molar mass of precipitate
iii)Determine the relative atomic mass of X and identify the element.

thanks for the help even if you can't answer it! thanks!

Just answer me thinking that I don't know anything.
1. How do I know how many ions does a compound break into by just looking at the chemical formula of the compound?
This requires practice with common cations and anions. Ionizable molecules are usually, if not always, polar. The acid HCl, for example, has a partially positive pole (H) and a partially negative pole (Cl). In solutions, HCl will ionize to form H+ and Cl-. HNO3 will produce H+ and NO3-.

For substances such as KMnO4, the polarity is not as easily apparent, but it can still be deduced that this molecule will produce K+ and MnO4-.

These anions (Cl-, KMnO4-, NO3-) and may other common ones can be found on a special page of almost any chemistry textbook.

Redbelly98
Staff Emeritus
Homework Helper
i need help!

Questions:

1. Calculate the volume of carbon dioxide at 273 K and 1.01 * 10^5 Pa which would be produced when 1.25g of calcium carbonate reacts completely with HCL.

and

2. When 41.18 cm^3 of a solution of silver ions with concentration of .2040 mol dm^-3 is added to a solution of XO4 -3 ions 1.172g of precipitate are formed.
i) calculate the amount in moles of Ag+ used in the reaction.
ii)Calculate molar mass of precipitate
iii)Determine the relative atomic mass of X and identify the element.

thanks for the help even if you can't answer it! thanks!
Hello soccergirl,

It's best to start a new thread when you have a new question.

Also, if you can explain how far you got and include what equations you think are useful, you're more likely to get help.