1 Mr. ShieldsRegents Chemistry U00 L04

2 Common Volume Measurement Devices Capacity

3 What is Calibration? lines The calibration of a measuring device is the distance between the two closest lines. What’s the calibration

4 Capacity = ? Calibration = ? 100 ml 1 ml source

5 Calibration If the calibration on a scale is 0.1g we can determine the mass of something to at least that level of accuracy. For example 219.4g But we can do better than that! We can also estimate one digit greater than that. For example we could measure g. The “3” is the estimated value. Note that Zero can be an estimated value as well as the numbers 1-9.

6 Calibration = ? 1 ml source 67.4 ml Estimated value

7 Capacity = ? Calibration = ? 10 ml 0.2 ml Reading? 8.80 ml. The zero is our estimated Value. It is significant and can not Ignored.

8 On this meter stick, the closest lines are 1 millimeter or meter apart. source What’s the calibration? Meter Stick

9 source What’s the calibration? 0.1 gram Triple beam balance What’s the reading? g What can we estimate to? 0.01 gram

10 This is part of a buret. Note… The numbers increase downward, so you read top to bottom. What’s The calibration? What’s the reading? 0.1 ml source ml

11 Now Let’s look at at a set of experimental B.P. Data collected by two students: Student 1Student deg C78.0 deg C AVG78.1 AVG The Accepted B.P. for this unk. is 77.2 deg C. Which set of data is more precise & which set Of data is more accurate? PERCENT ERROR

12 The data for student 1 “looks” better but how much better was that data than student 2’s data? Percent Error To make this comparison we need to look at the % error for each student’s set of data Formula for % ERROR: Experimental Value – Accepted Value x 100 Accepted Value

13 Student 1: x 100. = % Error 77.2 Student 2: x 100. = 1.17% Error 77.2 NOTE: ONLY THE SIZE OF THE ERROR IS IMPORTANT. IGNOR PLUS (+) AND MINUS (-) SIGNS. So which student has the more accurate data? Yep … Student 1 Problem: If student 1’s Exp. Value was 76.5 and the Accepted value Is 77.2 what is her experimental error?

14 Density Density (d) is the ratio of the mass (m) of a substance to its volume (V). density = mass / volume The most common units of density are grams per cubic centimeter (g/cm 3 ) or grams per milliliter (g/mL). d = m / V Remember … 1 cm 3 = 1 milliliter

15 Density & Temperature 1.How does temperature affect density? a.Increasing Temperature DECREASES density i. Volume increases with increasing Temperature - Why? ii. Mass stays constant, right? iii. Since D=m/vD must decrease. Why? - SO DENSITY DEC. WITH INC. TEMPERATURE for SOLIDS, LIQUIDS OR GAS

16 Density and Pressure 1.How does Pressure affect density? - SO For Gases DENSITY INC. with INC. PRESSURE (Can you Explain what happens when pressure decreases?) - Solids and liquids are not affected by pressure - Volume remains constant - No change in Density -What happens to gases when pressure is increased? -Volume decreases but mass remains constant Since D= m/v D must be increasing

17 Water is peculiar in that it’s volume increases as it goes from liquid At 4 deg To solid at zero. This is opposite to how most materials behave. D = M/V As V increases D decreases So ice floats on water DENSITYDENSITY

18 What is temperature? - How warm or cold something is - But what does this mean? - Molecules are in constant motion - Being in motion they have Kinetic Energy (K.E.= ½ mv 2 ) - As they collide with thermometer they impart their KE to it - That’s why we feel “warm” or “cold - The thermometer molecules begin to move faster & they impart Their energy to the material inside which warms and expands (or cools and contracts). We read this change on the scale. - So Temperature is a measure of average kinetic energy!

19 Temperature Scales Fahrenheit (F) - FP is set at 32 and BP is set at 212 Celcius (C) - FP is set at 0 and BP is set at 100 Kelvin (K) - Absolute Zero is the zero point; FP is then One degree on the Celcius scale is exactly equal to 1 degree on the Kelvin scale One degree on the Fahrenheit scale is equal to 1.8 degrees on the Centigrade and Kelvin scale

20 Conversion formulas How can we convert from one temperature scale to another? K = C (more precisely ) C = K – 273 Know These !