Density and Percent Error

Making a Gold Penny Lab FCP

results, formulas, and calculations

Multiple Choice

How do you measure density?

• D=M/V

• D=V/M

• V=D/M

• M=D/V

Density

• Density equals mass divided by volume

• d= m/v

• Mass unit grams

• volume unit cm³ or mL

• we use cm³ for a solid

• we use mL for a liquid or gas

Open Ended

500 grams of sugar occupies a volume of 0.315 liters. What is the density of the sugar in grams per milliliter?

Formula Density=mass/volume

Answer:

1.587 grams per milliliter

Percent Error

Key Points: Percent Error

*The purpose of a percent error calculation is to gauge how close a measured value is to a true value.

*Percent error (percentage error) is the difference between an experimental and theoretical value, divided by the theoretical value, multiplied by 100 to give a percent.

Percent Error Calculation Step 1

• Subtract one value from another. The order does not matter if you are dropping the sign (taking the absolute value. Subtract the theoretical value from the experimental value if you are keeping negative signs. This value is your "error."

Percent Error Calculation Step 2

• Divide the error by the exact or ideal value (not your experimental or measured value). This will yield a decimal number.

Percent Error Calculation Step 3

• Convert the decimal number into a percentage by multiplying it by 100.

Percent Error Calculation Step4

• Add a percent or % symbol to report your percent error value.

Percent Error

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Percent Error Calculation Practice

• In a lab, you are given a block of aluminum. You measure the dimensions of the block and its displacement in a container of a known volume of water. You calculate the density of the block of aluminum to be 2.68 g/cm³. You look up the density of a block of aluminum at room temp and find it to be 2.70 g/cm³. Calculate the % error of your measurement.

Open Ended

In a lab, you are given a block of aluminum. You measure the dimensions of the block and its displacement in a container of a known volume of water. You calculate the density of the block of aluminum to be 2.68 g/cm3. You look up the density of a block of aluminum at room temperature and find it to be 2.70 g/cm3. Calculate the percent error of your measurement.

Solution

• Subtract one value from the other:2.68 - 2.70 = -0.02

• Take the absolute value: 0.02 This is the error.

• Divide the error by the true value:0.02/2.70 = 0.0074074

• Multiply this value by 100% to obtain the percent error:

  0.0074074 x 100% = 0.74% (expressed using 2 significant figures).Significant figures are important in science.