#### Transcript Scientific Measurement - Central Valley School District

### Scientific Measurement

• **What is density? ** • **From your **

**experimental data, were the densities of the similar objects the same or different? Why? **

• **What does this tell **

**you about density? **

• **Can you look up the **

**density of a particular substance? **

• **Does the size of the **

**substance play a role in changing its density?**

• **For the irregular **

**shaped objects, did you get similar densities for each? Why or why not? If you didn’t, can you give a reason as to why? (accuracy and measuring tools)**

### Scientific Measurement

• **Qualitative and Quantitative** • **What is the difference between qualitative **

**and quantitative measurements?**

• **Qualitative- results that are descriptive and **

**nonnumeric**

• **Quantitative- results are given in a definite **

**form, usually as numbers and units **

• **Most of the things that we will be doing in **

**chemistry will be quantitative, but there will qualitative elements as well **

### Scientific Notation (Review)

• **What is scientific **

**notation?**

• **Example: **

**11000000000m**

• **s.n. : 1.1 *10**

**10 m**

• **Example: 8.1 *10**

**-3 m = 0.0081m**

• **Example: diameter **

**of a hair: 0.000008m = 8.0*10 -6 m**

• **Multiplication** • **3.0 *10**

**6 x 2.0*10 *2.0) x 10 (6+3) 3 = (3.0 = 6.0*10 9**

• **2.0 *10**

***10 (-3+5) -3 x 4.0 *10 = 8.0*10 2 5 = 8.0 **

• **(Add exponents)** • **Division** • **3.0*10**

**4 /2.0*10 2 3.0/2.0 x10 (4-2) *10 2 = = 1.5 **

• **6.0*10**

**-2 /2.0*10 3.0*10 (-2-4) 4 = = 3.0*10 -6**

• **(Subtract denominator **

**from the numerator)**

### Accuracy and Precision, Percent Error

• **Accuracy- measure **

**of how close a measurement comes to the actual or true value of whatever is being measured**

• **Precision- measure **

**of how close a series of measurements is to one another**

• **Percent error **

**compares the experimental value to the correct value**

• **Accepted value-**

**correct value based on reliable references, what types of references, your neighbor?**

• **Experimental value-**

**value measured in the lab**

### Accuracy and Precision

### Percent Error

• **Difference between **

**accepted and experimental values is called error**

• **Error= accepted **

**value-experimental value**

• **% Error= **

**[error]/accepted value * 100%**

• **Density of water= **

**1.0 g/mL (accepted)**

• **0.98 g/mL **

**(experimental)**

• **Percent Error = **

**[1.0 g/mL 0.98g/mL]/1.0 g/mL * 100% = 2%**

### Significant Figures in Measurements

• **The calibration of your measuring tool **

**determines how many sig. Figs. you can have.**

### Significant Figures in Measurements

•

**Example #1:**

• • • •

**This ruler measures to the .1 (in this case centimeters) However, I can see that the measurement lies between the 2.8 and 2.9 measurement, so I can make the estimate that it is approximately 2.83 cm. You see!!! All of those numbers are significant, because they all tell me about the measurement!**

**If I went out any further, it would not be accurate, because my measuring device is not that accurate!**

### Significant Figures in Measurements

• **This works for other measuring **

**devices as well. Just remember to always go one digit further than the device does**

• **Example #1: ** • **What temp does the **

**thermometer on the left indicate?**

• **The thermometer has whole **

**number digits , so for sig figs I can go to the tenths. **

• **The temp is 28.5**

**o C**

### Significant Figures in Measurements

• **This also works for Graduated Cylinders** • **Example #1** • **The drawing above indicates you are **

**looking at a graduated cylinder from the side (note the dip or meniscus, which you always read from the bottom) **

• **This graduated cylinder measures to the **

**whole number so we will read it to the tenth**

• **This graduated cylinder has a reading of **

**30.0 ml**

### Rules for Significant Figures

• • • • **Every nonzero digit reported in ** •

**measurement is assumed to be significant**

• **How many sig. Figs.?**

**-24.7m**

• • •

**-0.743m**

**-714m**

• **three** • **Zeros appearing between nonzero digits **

**are significant**

• **How many sig. Figs.?**

**-7003m -40.79m**

**-1.503m**

**Four**

### Rules for Significant Figures

• **Leftmost zeros appearing in front of nonzero ** •

**digits are not significant (Act as placeholders)**

• **0.0071m** • **0.42m** • **0.000099m**

**two**

• **Zeros at the end of a number and to the right **

**of a decimal point are always significant.**

• **43.00m** • **1.010m** • **9.000m** •

**Four**

### Rules for Significant Figures

• **Zeros at the rightmost end of a **

**measurement that lie to the left of an understood decimal point are not significant if they serve as placeholders to show the magnitude of the number.**

• **300m (1)** • **7000m (1)** • **27210m (4)** • **If 300 was found from careful measurement **

**and not a rough guess, then the zeros would be significant. To avoid this, write in scientific notation.**

• **3x10**

**2 m - not significant**

• **3.00x10**

**2 m – significant**

### Significant Figures in Calculations

• **Calculated values cannot be more **

*precise than the measured values used to obtain it.*

• * Addition and Subtraction* •

**round to the same number after the***decimal place as the measurement with the least number after the decimal place.*

• **12.54m + 349.0m + 8.24m = 369.76m = **

*369.8m*

• **74.626m – 28.34m = 46.286m = 46.29m**

### Significant Figures in Calculations

• **Multiplication and Division** • **round answer to the same # of **

**significant figures as the measurement with the least # of significant figures.**

• **7.55m * 0.34m = 2.6 (2)** • **0.365m * 0.0200m = 0.00730 (3)** • **2.4526m / 8.4m = 0.29 (2)**

### SI Units

• **Factor Name Symbol ** • **10**

**-1 deci d**

• **10**

**-2**

• **10**

**-3**

• **10**

**-6**

• **10**

**-9**

• **10**

**-12**

• **10**

**-15**

• **10**

**-18 centi c milli m micro µ nano n pico p femto f atto a**

### SI Units

• **Factor Name** • **10**

**6 Symbol mega M**

• **10**

**3**

• **10**

**2**

• **10**

**1 kilo k hecto h deka da**

### Glassware • **Which are used to measure **

**approximate volumes?**

### • **Which are used to measure more **

**precise volumes?**

### • **Which one would you use to **

**measure a large volume, such as 100 mL, accurately?**