Question

explain how the following experimental errors affect the final calculation of the kilocalories per gram for a food item. be specific as to whether the final value will be higher or lower than if the error had not been made.
a. the student misread the scale and recorded 110.3 g for the final mass of the beaker plus water instead of 101.3 g.
b. part of the unburned marshmallow fell off before the final mass was determined.
c. the food would not keep burning and had to be relit several times.
d. the thermometer got stuck in the aluminum foil while the food was burning and the final temperature was made with the thermometer in the air above the water and not in the water.

Explanation:

Step1: Analyze error a

The heat absorbed by water is calculated using $q = mc\Delta T$, where $m$ is mass. A higher - recorded mass ($m$) in the calculation of heat absorbed by water will lead to a higher calculated heat absorbed. Since kilocalories per gram of food is calculated based on the heat absorbed by water divided by the mass of food burned, a higher heat value will result in a higher final value of kilocalories per gram.

Step2: Analyze error b

If part of the unburned marshmallow fell off before final mass determination, the mass of the burned food is over - estimated. The heat released is calculated based on the mass of the burned food. With an over - estimated burned food mass, when calculating kilocalories per gram ($\frac{q}{m_{burned}}$), the final value will be lower because the denominator is larger than the actual value.

Step3: Analyze error c

If the food has to be relit several times, some heat is lost to the environment during the relighting process. So the heat absorbed by water is less than it should be if the food burned continuously. When calculating kilocalories per gram ($\frac{q}{m_{burned}}$), with a lower heat value ($q$), the final value will be lower.

Step4: Analyze error d

If the final temperature is measured in the air above the water instead of in the water, the measured final temperature is likely lower than the actual temperature of the water. Using $q = mc\Delta T$, a lower $\Delta T$ results in a lower calculated heat absorbed by water. When calculating kilocalories per gram ($\frac{q}{m_{burned}}$), the final value will be lower.

Answer:

a. Higher
b. Lower
c. Lower
d. Lower