AP Chem: MC Introduction

The correct volume of a container is 0.349L. If a student has measured the volume of the container three times, which of the following sets of measurements is most accurate?

 

  1. 0.348 L, 0.350 L, 0.348 L
  2. 0.345 L, 0.345 L, 0.346 L
  3. 0.344 L, 0.346 L, 0.350 L
  4. 0.330 L, 0.332 L, 0.334 L
  5. 0.350 L, 0.351 L, 0.352 L

 

1 is correct. Accuracy measures how close measurements are to an accepted value. Three measurements in the first set of data are closet to the correct value. 

Which of the following sets of data is the most precise?

  1. 0.348 L, 0.350 L, 0.348 L
  2. 0.345 L, 0.345 L, 0.346 L
  3. 0.344 L, 0.346 L, 0.350 L
  4. 0.330 L, 0.332 L, 0.334 L
  5. 0.350 L, 0.351 L, 0.352 L

2 is correct. Precision shows how close measurements are to each other. Although the data in the second set might not be closet to the accepted value, they are close to each other, so they are the most precise. 

How many significant figures are in the number 0.00230 mL?

  1. 2
  2. 3
  3. 4
  4. 5
  5. 6

2 is correct. Because the zeros immediately before and after the decimal point in this number are used to located the decimal point only, they are not significant. The zero at the end of the measurement, because it follows nonzero digits and is after the decimal point is significant. 

Which of the following measurements contains three significant digits?

  1. 1.700 x 10-3 g
  2. 2.30 x 103 g
  3. 2.6 x 105 g
  4. 4.210 x 104 g
  5. 9.00 x 105 g

2 is correct. Zeros that follow other digits and a decimal place are significant. Thus, all the zeros, other than the one in the power of ten are significant. 

One kilometer equals 1000 m. In this case how many significant figures are in the number 1000?

  1. One
  2. Two
  3. Three
  4. Four
  5. An infinite number

5 is correct. By definition, 1 km = 1000 m. Because the number is defined and not measured, they are exact numbers. Exact numbers can be assumed to have an infinite number of significant figures. 

How many significant figures will the answer be to the problem below:

0.0034 g x 2.34g/20,500 mL

  1. One
  2. Two 
  3. Three 
  4. Four
  5. Five

 

2 is correct. In multiplication and division, the answer has the same number of significant figures as the number in the problem with the fewest number of significant figures. The number 0.0034 has only two significant figures, and each of the other two numbers has three. Thus, the answer has to have two significant figures. 
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