Answer:
tar and nicotine which are produced when the tobacco leaves are burning.
Calcium and Nitrogen
Change in colour as well as liberating gas are the evidences that chemical reaction or change taken place.
The change in colour of the solution provides us information or evidence is that chemical change has taken place. There are many other ways which provides evidence of taking place of chemical change is the release of gas from the solution after adding powder or any substance.
There are some reactions in which new substance is formed which is also an identification of chemical change so we can conclude that change in colour as well as liberating gas are the evidences that chemical reaction or change taken place.
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D.All of above. Hope it helps!!!
3. Determine the average percent yield of MgO for the two trials.
Answer:
Part 1
Theoretical yield of MgO for trial 1 = 0.84 g
Theoretical yield of MgO for trial 2 = 1.01 g
Part 2
Percent yield trial 1 = 28.6 %
Percent yield trial 2 = 49.9 %
Part 3
Average percent yield of MgO for two trial = 39.25 %
Explanation:
Part 1.
Data Given
Trial 1 Trial 2
mass of empty crucible and lid: 26.679 g 26.685 g
mass of Mg metal, crucible and lid: 26.931 g 26.988 g
mass of MgO, crucible and lid: 27.090 g 27.179 g
Theoretical yield of MgO for trial 1 and 2 = ?
Solution:
As Mg is limiting reagent so amount of MgO depends on the amount of Mg.
So, now we will look for the reaction to calculate theoretical yield
MgO form by the following reaction:
Mg + O₂ ---------> 2 MgO
1 mol 2 mol
Convert moles to mass
Molar mass of Mg = 24 g/mol
Molar mass of MgO = 24 + 16 = 40 g/mol
So,
Mg + O₂ ---------> 2 MgO
1 mol (24 g/mol) 2 mol(40 g/mol)
24 g 80 g
So,
24 g of Mg gives 80 g of MgO
To Calculate theoretical yield of MgO for Trial 1
First we look for the mass of Mg in the Crucible
Mass of Mg = mass of Mg metal, crucible and lid - mass of empty crucible and lid
Mass of Mg = 26.931 g - 26.679 g
Mass of Mg = 0.252 g
As we come to know that 24 g of Mg gives 80 g of MgO, then amount of Mg from trial 1 that is 0.252 g will produce how many grams of MgO
Apply unity formula
24 g of Mg ≅ 80 g of MgO
0.252 g of Mg ≅ X g of MgO
Do cross multiplication
X g of MgO = 0.252 g x 80 g / 24 g
X g of MgO = 0.84 g
So the theoretical yield of MgO is 0.84 g
--------------
To Calculate theoretical yield of MgO for Trial 2
First we look for the mass of Mg in the Crucible
Mass of Mg = mass of Mg metal, crucible and lid - mass of empty crucible and lid
Mass of Mg = 26.988 g - 26.685 g
Mass of Mg = 0.303 g
As we come to know that 24 g of Mg gives 80 g of MgO, then amount of Mg from trial 2 that is 0.303 g will produce how many grams of MgO
Apply unity formula
24 g of Mg ≅ 80 g of MgO
0.303 g of Mg ≅ X g of MgO
Do cross multiplication
X g of MgO = 0.303 g x 80 g / 24 g
X g of MgO = 1.01 g
So the theoretical yield of MgO is 1.01 g
__________________________
Part 2
percent yield of MgO for trial 1 and 2 = ?
Solution:
For trial 1
To calculate percent yield we have to know about actual yield of MgO
Mass of MgO = mass of MgO, crucible and lid - mass of empty crucible and lid
Mass of MgO = 27.090 g - 26.685 g
Mass of MgO = 0.24 g
And we also know that
Theoretical yield of MgO for trial 1 = 0.84 g
Formula used
Percent yield = actual yield / theoretical yield x 100
put values in above formula
Percent yield = 0.24 g / 0.84 g x 100
Percent yield = 28.6 %
--------------
For trial 2
To calculate percent yield we have to know about actual yield of MgO
Mass of MgO = mass of MgO, crucible and lid - mass of empty crucible and lid
Mass of MgO = 27.179 g - 26.685 g
Mass of MgO = 0.494 g
And we also know that
Theoretical yield of MgO for trial 2 = 1.01 g
Formula used
Percent yield = actual yield / theoretical yield x 100
put values in above formula
Percent yield = 0.494 g/ 1.01 g x 100
Percent yield = 49.9 %
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Part 3
average percent yield of MgO for the two trials =?
Solution:
As we know
Percent yield trial 2 = 28.6 %
Percent yield trial 2 = 49.9 %
Formula used
Average percent yield = percent yield trial 1 + percent yield trial 2 / 2
Put values in above formula
Average percent yield = 28.6 + 49.9 / 2
Average percent yield = 78.5 / 2
Average percent yield = 39.25 %
Average percent yield of MgO for two trial = 39.25 %