Couple questions on reactions..

[BacardiGirl]

I am studying for a gen chemistry exam covering reactions, mass to mass conversions and yield and am stumped on three problems on the study sheet. In fact, I am not even quite sure how to set them up properly. Any suggestions/help? Much appreciated.

1. How many grams of C are needed to react with 5.00 g of Na2 SO4 according to the following equation:
Na2 SO4 + 2C ----> Na2 S + 2CO2
when I tried to set this up as a conversion problem, I came up with an answer of 1.69 g which was incorrect.

2. For the following reaction, how many g of H2O are produced when 4.0 g of HCl reacts with 2.5 g Ca(OH)2?
2HCl + Ca(OH)2 ----> CaCl2 + 2H2O
I am confused as how to incorporate both factors into one conversion problem?? I understand how to do this when it gives you one factor (such as HCl reacting completely), but not when two are listed.

3. How many grams of the excess reagent are leftover according to the reaction below given that you start with 10.0 g Al and 19.0 g O2?
4Al + 3O2 ----> 2 Al2 O3
I wrote this out by breaking them down to separate problems, one for Al and one for O, such as when you figure out percent yield, but I was unable to come out with the correct answer.

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[161927]

I am studying for a gen chemistry exam covering reactions, mass to mass conversions and yield and am stumped on three problems on the study sheet. In fact, I am not even quite sure how to set them up properly. Any suggestions/help? Much appreciated.

1. How many grams of C are needed to react with 5.00 g of Na2 SO4 according to the following equation:
Na2 SO4 + 2C ----> Na2 S + 2CO2
when I tried to set this up as a conversion problem, I came up with an answer of 1.69 g which was incorrect.

(5 g sodium sulfate)(1 mol/(Molar Mass of Na2SO4))(2 mol C/1 mol sodium sulfate)

2. For the following reaction, how many g of H2O are produced when 4.0 g of HCl reacts with 2.5 g Ca(OH)2?
2HCl + Ca(OH)2 ----> CaCl2 + 2H2O
I am confused as how to incorporate both factors into one conversion problem?? I understand how to do this when it gives you one factor (such as HCl reacting completely), but not when two are listed.

4.0g/36.45 = mol HCl
2.5g/(molar mass Ca(OH)2) = mol Ca(OH)2
^^ determine limiting reagent remembering 2 moles of HCl are needed to react w/antacid

(mol LR)(2 mol H2O/? mol LR)(18 g/mol H2O) = answer

3. How many grams of the excess reagent are leftover according to the reaction below given that you start with 10.0 g Al and 19.0 g O2?
4Al + 3O2 ----> 2 Al2 O3
I wrote this out by breaking them down to separate problems, one for Al and one for O, such as when you figure out percent yield, but I was unable to come out with the correct answer.

[/quote]
same process as #2
convert to moles, determine LR
use stoichiometric ratios to get answer

 

[BacardiGirl]

thank you!