Homework Help: chemistry

Posted by cal on Tuesday, February 12, 2008 at 10:12am.

What is the sum of the coefficients (including “1”) of the balanced equation?
__CaCO3 + __NaF __ CaF2 + __Na2CO3

4
5
6
7
8

If you start with 20.0 grams CaCO3, how many moles of CaCO3 do you have?

20.0
2.00
.200
.0200
.0386

If you start with .500 moles of NaF, how many moles of CaF2 will form
.500
1.00
1.50
2.00
0.250

What is the sum of the coefficients (including “1”) of the following reaction?
Sodium sulfate + calcium hydroxide ???

4
5
6
7
9

Predict the precipitate that forms: HCl + AgNO 3 ???
HNO3
HCl
AgNO3
AgCl
no precipitate forms

chemistry (#1 of 5) - drwls, Tuesday, February 12, 2008 at 10:45am
The balanced reaction is
CaCO3 + 2 NaF -> CaF2 + Na2CO3
You forgot the reaction arrow.
The sum of the coefficients is 5.

We will be glad to critique your work on the remainder of the problem. I assume you can compute molar mass of a compound and convert mass to moles.
chemistry - timmyj, Tuesday, February 12, 2008 at 2:28pm
number 2 is .2 because I found molar mass. Number 3 4 and 5 is where I get lost.
- chemistry - cal, Tuesday, February 12, 2008 at 2:29pm
  I posted under my friends name accidentally.. but number 2 is .2 because I found molar mass. Number 3 4 and 5 is where I get lost
chemistry - DrBob222, Tuesday, February 12, 2008 at 4:33pm
0.2 is correct for #2.

Here is how you work #3 and all problem similar to it. First, the copy.

CaCO3 + 2NaF ==> CaF2 + Na2CO3
If you start with .500 moles of NaF, how many moles of CaF2 will form
.500
1.00
1.50
2.00
0.250

ASSUMING you have an unlimited supply of CaCO3 (not the 20.0 g in problem 2), convert 0.500 mols NaF to mols CaF2 by using the coefficients in the balanced equation.
0.500 mols NaF x (1 mol CaF2/2 mol NaF) = (notice how the units of NaF cancel and mols CaF2 are left--this is the way we convert mols of one thing to mols of another) = 0.500 NaF x 1/2 = 0.250 CaF2.

On the others, if you get stuck, repost as a new post (at the top of the board) and tell us exactly what your trouble is in detail. That way we can help you better.

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