scientific skills.....aim 2
	what are density, % error, and scientific method?
	.....aim 1	home	aim 3.....

Density       

It is the quantity of matter present in a given volume. See table T

    d = m / V

mass is defined as the quantity of matter in an object expressed in kilograms (kg), grams (g), or milligrams (mg).

volume is the amount of space occupied by an object expressed in liters (L), milliliters (ml), or cubic centimeters (cm³).

Note: The milliliter (ml) and the cubic centimeter (cm³) are the same size; they are just expressed in different units.

Example

If an object has a mass of 20 grams and a volume of 10 milliliters, its density is 2 g/ml or 2 g/cm³

Percent error

See table T

% error =  (measured value – accepted value / accepted value) x 100

measured value = experimental value

accepted value = theoretical value

Example

You are told to weigh a specific mass of BaCl₂.2 H₂O and to find the percent by mass of water in the crystal. After heating the mass of hydrated crystal to constant mass in a crucible, you obtain the following data. What is the percent error for the mass of water in the hydrate?

 Percent Error  =  (12 - 14 / 14) 100 = 14.3 %

Scientific method

There are five steps to the scientific method.

Step 1:  Define a problem

Step 2:  Collect information about the problem

Step 3:  Find a possible answer (hypothesis)

Step 4:  Do controlled experiments to test the hypothesis

Step 5:  Report findings to other scientists so that experiments can be repeated

TEST YOUR UNDERSTANDING

6/02

A student calculated the percent by mass of water in a hydrate as 14.2%. A hydrate is a compound that contains water as part of its crystal structure. If the accepted value is 14.7%, the student's percent error was

            (1) 0.5/14.2 x 100        (2) 14.7/14.2 x 100     (3) 0.5/14.7 x 100        (4) 14.2/14.7 x 100  

8/02

1 A student used a balance and a graduated cylinder to collect the following data

a) Calculate the density of the element. Show your work. Include the appropriate number of significant figures and proper units.

b) If the accepted value is 6.93 grams per milliliter, calculate the percent error.

c) What error is introduced if the volume of the sample is determined first?

2 During a laboratory activity, a student combined two solutions. In the laboratory report, the student wrote "A yellow color appeared." The statement represents the student's recorded

            (1) conclusion    (2) observation    (3) hypothesis       (4) inference

1/03

A student intended to make a salt solution with a concentration of 10.0 grams of solute per liter of solution. When the student's solution was analyzed, it was found to contain 8.90 grams of solute per liter of solution. What was the percent error in the concentration of the solution?

                (1) 1.10%      (2) 8.90%     (3) 11.0%                    (4) 18.9%

8/03

66 A student determines the density of zinc to be 7.56 grams per milliliter. If the accepted density is 7.14 grams per milliliter, what is the student's percent error?

° Show a correct numerical setup.

° Record your answer.

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