Discovering Design With Chemistry Chapter 1 Review

12. what is the correct answer to the following equation 21.0234g - 12g

remember that when we subtract measurements we must look at precision. the first measurement is very precise having its last significant figure in the ten thousands place. The "12" is the least precise number in the prom because it's last significant figure is in the ones place. thus the answer must be reported to the ones place. when you do the subtraction you get 9.0234g, but it must be rounded to the ones place so the answer is 9g

13. a u.s. dime has a diameter of 17.9mm. what is a diameter in m?

the answer is 0.0179m. we put the measurement over "1" to make it a fraction than multiply by the conversion relationships so that mm cancel. you get the converstion relationship by replacing the prefix with its meaning. since "mili" means "0.001," 1mm = 0.001 m 17.9mm. 0.001m --------- x --------. = 0.0179 m 1. 1mm

14. a soup can has a mass of 490grams. what is its mass in kg?

the answer is 0.49. since kilo means 1000 the relationship is 1 kg = 1,000g

c. Significant figure

A digit in a measurement that contributes to the measurement's precision

e. Mass

A measure of how much matter exists in an object

d. Weight

A measure of how strongly gravity pulls on an object

f. Density

A measure of how tightly-packed the matter in a substance is

b. Unit

A quantity that describes the measurement being made

1. a. Matter

Anything that has mass and takes up space

11. A Carpet-layer measures a room to be 4.6m long and 3.2m wide. He multiplies the two measurements and reports the are of the room to be 14.72. What two things are wrong with his answer?

First there is no unit. a measurement means nothing without the unit. second there are too many significant figures. the measurements for .6 M and 3.2 M each have two significant figures, so the answer should have two.

9. When a figure is significant, does that mean it is mathematically important?

It does not. A Significant figure is one that has been measured. It doesn't have to be mathematically important. For example, the zero in 1.0 is significant, but it is not mathematically important. For example, the zero in 1.0 is significant, but is is not mathematically important, as 1.0 and 1 have the same mathematical value.

5. An object has a mass of 123.4 kg, which is the same as 8.456 slugs. Which measures more mass: 1 slug or 1 kg?

It takes 123.4 kg ti measure the same mass as 8.456 slugs. Since it takes more kilograms ti measure the same mass, this means a kilogram is a smaller mass unit. Thus, a slug measures more mass.

3. You are reading a scientist's lab notebook and see a measurement of 14.5 m. What was the scientist measuring: length, mass, volume, or time?

Liters are used to measure volume, and mL is just a unit that has the prefix "mili" in front of liters. Thus, this is a volume measurement.

6. A box has a volume of 1.01m^3 . Two students measure the box. The firsts says the volume is 1 m^3, while the second says the volume is 1.23m^3. Assuming they are reporting the correct number of significant figures for the measuring devices used, which student used the more precise device? Which student provided the more accurate answer?

The second student used the more precise device, because his answer has more decimal places to it. However, he didn't use it very well, because his answer is not correct. The first student has the more accurate answer, because it is equal to the correct answer, at least to the significant figure that was reported.

10. Two students are measuring the mass of an object. One reports his answer as 4.56g, while the other reports her answer 4.58g. The teacher gives each student 100% credit. How can they both be right?

There is always uncertainty in the last significant figure. When measuring things, you always estimate the last figure. As a result, two experimenters can make the same measurement and have slightly differ answers in the last significant figure.

8. When you put the ice cubes in a glass of water, the ice cubes float. What does that tell you about the density of ice compared to the density of water?

To float, an object must have a lower density than the liquid. Thus means ice has a lower density than water.

2. What are base metric units used to measure length, mass, and time?

We measure length with meters, mass with grams, and time with seconds

4. You are measuring the volume of an object using a scale that is marked off with lines that represent 10 mL each. To what level of precision (one mL, tenths of an mL, hundreths of an mL, etc.) should you report your measurement?

You should report your answer to one mL, since you can always estimate between the lines.

7. How many significant figures are in the following measurements? a. 1.06*10^4mL b. 12.,000cm c. 0.0340 kg d. 1.0*10^1in

a. The "1" and "6" are significant, which makes the "0" between them significant. You don't worry about what follows the "*" sign, so this number has three significant figures. b. The "1" and "2" are significant, but the zeroes are not. They are at the end of the number, but they are not to the right of the decimal. Thus, there are two significant figures. c. The first two zeroes are not significant, as they are neither between two significant figures nor at, the end of the number and right of the decimal. The "3" and "4" are significant, as is the last zero, since it is at the end of the number and to the right of the decimal. Thus there are three. d. The "1" is significant, as is the zero, since it is at the end of the number and to the right of the decimal. You don't worry about what follows the "*" sign, so there are two significant figures.