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a) $\ce{AgNO3(aq) + CuCl2(aq) -> }$

So the first step is to combine the inners and outers.

So I have $\ce{AgCl}$ and $\ce{CuNO3}$

I know $\ce{NO^-_3}$ has a -1 charge so then wouldn't $\ce{Cu}$ have a +1 charge?

But I see in the solutions that it says the resulting products would be $\ce{AgCl}$ and $\ce{Cu(NO3)2}$

Am I supposed to just know this? I don't know why I would assume $\ce{Cu}$ has a +2 charge?

I know that copper has a +1 and +2 charge. since $\ce{NO^-_3}$ has a -1 charge, I assumed that cooper would have a +1 charge. How do I know when copper has a +1 charge and a +2 charge?

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    $\begingroup$ You have copper chloride as a reactant: one copper ion with two chloride ions. Each chloride ion has -1 charge and copper chloride is neutral. So what is the copper ion’s charge? $\endgroup$
    – Ed V
    Oct 1, 2021 at 21:03
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    $\begingroup$ Too broad. This reaction is simply a precipitation reaction: AgCl is insoluble. $\endgroup$
    – Ed V
    Oct 1, 2021 at 21:07
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    $\begingroup$ To add a little to the answer by @M. Farooq, we try to vault over that heap of hard acquired chemistry knowledge by providing beginning chemistry students with some guidelines, e.g, all sodium and nitrate salts are water soluble, carbonates plus acids result in evolution of carbon dioxide, etc. These are useful over-simplifications (white lies, if you will) and students who go on in chemistry learn that, sometimes a bit unhappily. But we have to start somewhere: chemistry is wonderfully complex and vast. $\endgroup$
    – Ed V
    Oct 1, 2021 at 21:56
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    $\begingroup$ For future reference: Note, chemical information may be advantageously formatted using on ChemSE with mhchem. Take moment to familiarize with this. You are encouraged to use it in the body of questions, answers, and comments. Because it is something special not all web browsers understand well, do not use it in the title of questions or answers. $\endgroup$
    – Buttonwood
    Oct 1, 2021 at 22:17
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    $\begingroup$ @josh copper(I) can be stabilized in water solution using an appropriate soft base ligand; thiourea is one such agent. But with direct water solvation it has to be mostly copper(II). $\endgroup$ Oct 2, 2021 at 0:40

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Your questions (or complains) are encompassing human knowledge acquired over a century and may be more! Science has several collections of known facts, huge body of information and knowledge. You have to know them just like in math you learned 2+2=4, and the area of the rectangle is length into breadth, and the ratio of circumference of a circle to diameter is always $\pi$.

Of course, you cannot read and find the history of someone did an elemental analysis and established the formulae of two solid compounds obtained from dissolving silver metal in nitric acid and copper oxide in hydrochloric acid respectively. Someone must have done an elemental analysis of the solids to find out the ratio of the elements in $\ce{AgNO3}$ and $\ce{CuCl2}$. You are right that you cannot find beforehand the charge on $\ce{Ag}$ in $\ce{AgNO3}$ if you had prepared the compound from scratch 150 years ago.

When chemists started studying the fact that some salts dissolved in water conduct electricity, with further refinements and experiments they were able to find the sign and the magnitude of the charge on the ions. Someone has experimentally determined it to be $\ce{Ag^+}$ and $\ce{Cu^{2+}}$ in these two salts.

You see there is a big body of factual knowledge in chemistry acquired by millions of experiments. You need a base to learn how chemical formulae are written. Once you collect information, you will start to see trends and patterns. Once you have “memorized” the basic charges and signs of common elements, patterns of precipitation, the question is answerable in a single line, as given by Prof. EdV. It is a precipitation reaction and silver forms insoluble salts when chloride ion is present.

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