Question

I'm having trouble understanding Stoichiometry and Moles please help :'(

1. Hydrofluric acid, HF, cannot be stored in glass bottles because compounds called silicates in the glass are attacked by the HF. Sodium silicate (Na2SiO3), for example reacts as follows Na2SiO3 + HF----->H2SiF6+NaF+H20

a. balance the above reaction
b. How many moles of HF are needed to react with 0.300 mol of Na2SiO3?
c. How many grams of NaF form when 0.500 mol of HF reacts with excess Na2SiO3?

Answer 1

I balance the reaction by first balancing Na, the F, then O. Can you take a stab at it?

Answer 2

I don't really understand how to do it though :/ how would you know which ones to tackle first?

Answer 3

It is usually best to do H and O last. Some of it is trial and error.

Answer 4

so would I just have to view the periodic table?

Answer 5

Generally, do the elements with low numbers first.

Answer 6

No, you don't need the periodic table to balance.

Answer 7

You just need the number of each element in the products and reactants to be the same.

Answer 8

For example, there are 2 Nas in the reactants, but only 1 in the products. So make NaF, but 2NaF.

Answer 9

When you are balancing you can change the coefficient of each compound, but not the subscripts. That would change the chemical formula.

Answer 10

oh ok.. so referring back to the Na2SiO3 +HF---> H2SiF6 +NaF +H2O i don't understand how we the second portion based off of the first reaction

Answer 11

I don't understand that last comment.

Answer 12

how would Na2SiO3+HF combine with this-->H2SiF6+NaF+H20

Answer 13

I don't think you have the tools yet to figure out the products from the reactants. For now, you are expected to accept it without understanding why...

Answer 14

Balancing a reaction that is given to you is much simpler than figuring out the products from the reactants.

Answer 15

A helpful tool for balancing is a chart with the number to each element on each side. Like this:
Reactants
Na - 2
Si - 1
O - 3
H - 1
F - 1

Answer 16

Products
H - 4
Si - 1
F - 7
Na - 1
O - 1

Answer 17

oh ok that makes sense :)

Answer 18

Your job is to make the number of each element equal on each side by changing the coefficients only.

Answer 19

:)

Answer 20

so after we include each element in that chart ^^ what else would be need to do I don't really understand what you mean by the coefficients

Answer 21

The number you multiply by each of the compounds. For example, to balance the Na I would
Na2SiO3 + HF -> H2SiF6 + 2NaF + H2O

Answer 22

For 2NaF, the 2 is the coefficient.

Answer 23

It means we have 2 molecules of NaF in the products.

Answer 24

oh ok 2 is in from of the NaF because it's like one whole bond?

Answer 25

No, they are separate molecules. But there are two of them. It is like saying NaF + NaF

Answer 26

= 2NaF

Answer 27

Just like x + x = 2x

Answer 28

oh ok :)

Answer 29

Any ideas on what to do next to finish balancing?

Answer 30

i'm not really sure :/

Answer 31

Try balancing the F next. How many do you have total in the products now?

Answer 32

7

Answer 33

We had 7 before we changed NaF to 2NaF. Now we have 8.

Answer 34

oh ok

Answer 35

So when we have 8 in the products, we need 8 in the reactants. What coefficient could you change in the reactants to give 8 Fs?

Answer 36

Are you thinking or stuck?