# Stoichiometry hlp

1. May 23, 2007

### Mack

Data Table
..............................................NaHC O3................CaCO3
1. Mass of micro plate..............2.05g.................2.05g
2. Mass of micro plate +salt.........3.05g................3.05g
3. Mass of Salt .........................1g..................1g
4. Moles of salt.........................1/84 mol...........1/100 mol
5. Mass of unreacted setup..........20.66g.............17.9g
6. Mass of reacted setup..............20.58g............17.85g
7. Mass of CO2 lost........................08g..................0 5g
8. Moles of CO2 lost.....................0018mol............0011 mol
9. Mass of Co2 produced as % of mass of sample 8% 5%

(reacted with vinegar)
Questions:
1. Write balanced equation for each raction.
2. From the stoichiometric relationships in the data table, find the # of moles of CO2 actually produced by each reaction.
3. How did the number of moles of CO2 actually produced by each reaction compare with the number of moles that ideally should be produced?

I don’t get how to do numbers 2 and 3. I believe I did number 2 in 8 on the chart but then what is the ideall number of moles? That’s were im confused plz help

2. May 23, 2007

use molar mass and use the ratios from the balanced equation

3. May 23, 2007

### Mack

well the balanced equation would be for the CaCO3 reaction would be

CaCO3+2HC2H3O2=>Ca(C2H3O2)2+CO2+H2O
molar mass of CaCO3 is about 100g/mol and CO2 is 44g/mol

but i dont no what to do from here or what ratios u r talking about

im sry my teacher didnt explain this at all and ive called all my friends but they dont get it either

Last edited: May 23, 2007
4. May 23, 2007

well, Ca has a charge of +2 and the acetate ion has a charge of -1, so you need to rewrite the chemical formula for calcium acetate.

you can ratio the coefficients to link any two pieces in the reaction.

example:

2H2 + O2 -> 2H2O

the ratio ofhydrogen to oxygen is 2:1. the ratio of oxygen to water is 1:2. the ratio of water to hydrogen is 2:1. does that make sense to you?

5. May 23, 2007

the equation isnt balanced

6. May 23, 2007

### Mack

ya i get that so the ration of CaCO3 and CO2 is like 1:1?

well i think i know what to do but i end up with something like .44mols
and what we did in class for the lab makes out to be .0011mols

i dont get how to get how many grams of CO2 is in 1g CaCO3
if thats what im supposed to do to get the ideal number of moles?

7. May 23, 2007

### Mack

sry i forgot a 2 i just edited it in so its balanced now sry

8. May 23, 2007

can you show the work with units cause its late and i got my own ap chem final tomorrow.

9. May 23, 2007

read the sections called "molar ratios" and the one called "given grams get grams" - those seem like good tutorials

http://dbhs.wvusd.k12.ca.us/webdocs/Stoichiometry/Stoichiometry.html [Broken]

Last edited by a moderator: May 2, 2017
10. May 23, 2007

### Mack

i ment i end up with .01 not .44
what i do is i find that CO2 makes up .44g of the 1g ofCaCO3

then i divided .44g by 44g and got .01mols

when i did it in the lab only .o5g evaporated not .44g?

is the work i did correct or the lab correct?

11. May 23, 2007

um...its late, im tired, those numbers appear so random to me. show all your calculations? just check the tutorials. if you can convert something to moles, you can find basically anything.

12. May 23, 2007

### Mack

molar mass of CO2 is 44g/mol
molar mass of CaCO3 is 100g/mol

1g/100g/mol=x/44g/mol
x=.44g

.44g of CO2 makes up CaCO3?

so .44g divided by 44= .01mols?

idk im prolly really wrong

13. May 23, 2007

i'm confused. what exactly happened in the lab? did you react calcium carbonate and acetic acid? then wahts "NaHC O3................CaCO3"?

14. May 23, 2007

the grams...grams of what? converting to moles of what?

15. May 23, 2007

### Mack

we did it with CaCo3 and NaHCO3

it wouldnt let me space the chart out so it would scrunch it all together so i used ...... to seperate them if i no how to do one i can get the other easily

16. May 23, 2007

so you reacted each one with vinegar?

17. May 23, 2007

### Mack

yes we reacted each on with vinegar until there was no more bubbles and found how many g of CO2 were evaporated

we used a pipet filled with vinegar and weighed it in with unreacted setup and then weighed it in with reacted setup so that only missing mass was the CO2

18. May 23, 2007

do you know what a limiting reagent is?

19. May 23, 2007

however much acetic acid used was how much reacted. base your stoich on the amount of acetic acid consumed and you should be fine. goodluck & goodnight

20. May 24, 2007

### chemisttree

Start by clearly writing each reaction. You have done one already. You can abbreviate acetic acid as 'HOAc' and acetate as 'OAc-'. Calcium actate becomes Ca(OAc)2. Much cleaner, yes?

The second question is not very clearly worded. Read that as "Find the # of moles of CO2 actually produced by each reaction". I don't know how the 'stoichiometric relationships in the data table" can help (or even what it means!). There are no 'stoichiometric relationships' in the data table... only data!

The third question requires those 'stoichiometric relationships' you discovered by answering question #1 (no, those pesky relationships are not in the data table!). Rewriting your answer for the calcium carbonate reaction you have:

CaCO3 + 2 HOAc ----> Ca(OAc)2 + CO2 + H2O

Here is where you will find 'stiochiometric relationships'! You will see that for each mole of CO2 produced you will have started with one mole of CaCO3. You know the weight of the CaCO3 you started with and you can calculate the # of moles. From this you will know how many moles of CO2 you expect to find. Compare that to what you have for mass of CO2 lost (expressed in moles) in your data table.

Now, do the same thing for sodium bicarbonate...