What is wrong with the experimental design is that the student changed more than one independent variable.
WHAT AN EXPERIMENT SHOULD CONTAIN?
- An experiment is a procedural method of solving a scientific problem or answering a scientific question. An ideal experiment should contain two variables namely: independent variable and dependent variable.
- Dependent variable: This is the variable that the experimenter measures in the experiment. The dependent variable responds to changes made to the independent variable.
- Independent variable: This is the variable that is manipulated in an experiment in order to bring about a response.
In the experiment conducted by the student in this question in order to determine how the temperature of water affects the time for sugar to dissolve. The independent variable is the DIFFERENT TEMPERATURE OF WATER while the dependent variable is the TIME TAKEN FOR SUGAR TO DISSOLVE.
N.B: An experiment should have only one independent variable and all other variables should be kept constant. This is to have a reliable result.
- However, this student used two independent variables (temperature and amount of water) for the experiment, which is wrong for the experimental design.
Therefore, the fact that the student changed more than one independent variable is wrong for the experimental design.
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A. -20kj
Explanation:
The reaction is exothermic
therefore enthalpy = 20 - 40 = -20
Answer:
Percent yield = 86.2%
Explanation:
Given data:
Mass of zinc = 3.68 g
Mass of zinc chloride = ?
Percent yield = ?
Actual yield = 7.12 g
Solution:
Chemical equation:
Zn + 2HCl → ZnCl₂ + H₂
Number of moles of zinc:
Number of moles = Mass /molar mass
Number of moles = 3.68 g / 65.38 g/mol
Number of moles = 0.06 mol
Now we will compare the moles of ZnCl₂ with zinc.
Zn : ZnCl₂
1 : 1
0.06 : 0.06
Theoretical yield of zinc chloride:
Mass of ZnCl₂ = moles × molar mass
Mass of ZnCl₂ = 0.06 mol × 136.286 g/mol
Mass of ZnCl₂ = 8.2 g
Percent yield:
Percent yield = actual yield / theoretical yield × 100
Percent yield = 7.12 g/ 8.2 g × 100
Percent yield = 86.2%
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