# Homework Help: Molarity of a solution of silver perchlorate

1. Mar 27, 2007

### n108

What is the molarity of a solution of silver perchlorate, AgClO4, if 3.2 moles of silver perchlorate is dissolved in 1.5 liters of water? Is it 2.133 M, 4.756 M, 4.8 M, or 4.810 M ?
i guessed 2.133 M

2. How many moles of potassium iodide, KI, must be used to make 1.500 L of a 0.2 M solution?
.3 m
.2 M
.2 m I know its not this one...
.2 g

3. What is the molarity of the solution produced when 151 g of sodium chloride, NaCl is dissolved in enough water to prepare .375 L of solution?
.469 M this one is wrong
9.456 M
3.57 M
6.89 M

4. How many grams of potassium chloride, KCl, are needed to prepare 0.630 L of a 2.50 M solution of potassium chloride?
1.575 M
117 g
2.54 m
23.19 g this one is wrong

2. Mar 27, 2007

### hage567

Can you explain what it is about these questions that gives you trouble? We can't really help if we don't know how you're approaching the problem.
You must have some ideas, how else can you say those answers are the wrong ones?

3. Mar 28, 2007

### Smith4046

n108;

Google "molarity", go to the first reference, and look at the equation on the top of the site. Good luck.

Steve

4. Mar 28, 2007

### n108

ok, I think my mind is clearing up a little bit...better.
thanks

5. Mar 28, 2007

### n108

balancing equations

Problem #1:
Aluminum oxide is formed from the reaction of metallic aluminum with oxygen gas. How many moles of Aluminum are needed to form 3.4 moles of Aluminum oxide?
Hint: This is a simple ratio problem. Just use the molar ratio from the balanced equation. Mass is not involved.

Ok, so I know that aluminum has 3 valence electrons and oxygen, which is diatomic, has 6 valence electrons. And I know that there needs to be 8 electrons to make a compound. but 3 + 6 is 9, not 8. I also learnt about the different types of bonds, ionic bonds, covalent bonds, metallic bonds. So I can guess that this is a covalent bond where I electron is shared by both.

But I still don't understand how to write the chemical compound equation, and how to balance it, for Aluminum oxide.
Help!

6. Mar 28, 2007

### symbolipoint

Aluminum Oxide:
Al2O3

That shows for 1 formula unit, two of Aluminum and three of Oxygen.

(Is there a way to form subscripts in this forum?)

7. Mar 28, 2007

### f(x)

You dont even need to balance the equations, simply use principle of conservation of (particluar) atom species, for eg in the above reaction, its Al.
Also, when you form compounds, care about the valence electrons of individual atoms, eg. you said Oxygen atom has 6 electrons. So its short of two, while Aluminium has 3 extra.
In simplest form the balanced eqn looks like this (this is not needed but still )
$$2Al \ + \ \frac{3}{2}O_2 \longrightarrow \ Al_2 O_3$$

8. Mar 29, 2007

### n108

Thank you!
So now I know the formula for aluminum oxide: Al2O3. How do I find out how many moles are needed to form 3.4 moles of aluminum oxide?
The hint says: "This is a simple ratio problem. Just use the molar ratio from the balanced equation. Mass is not involved."
How do I the molar ratio of aluminum oxide?
Al2 to O3 = 2/3?
That doesn't seem right...