Calibration, Percent Error, Density & Temperature

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Mr. Shields Regents Chemistry U00 L04

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Common Volume Measurement Devices

Capacity

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What is Calibration?

The calibration of a measuring device is the distance between the two closest lineslines.

What’s the calibration

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Capacity = ?Capacity = ?

Calibration = ?Calibration = ?

100 ml100 ml

1 ml1 mlsource

source

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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 219.43g.

The “3” is the estimated value. Note that Zero can be anestimated value as well as the numbers 1-9.

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Calibration = ?Calibration = ? 1 ml1 mlsource

source

67.4 ml

Estimated value

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Capacity = ?Capacity = ?

Calibration = ?Calibration = ?

10 ml10 ml

0.2 ml0.2 ml

Reading?

8.80 ml. The zero is our estimatedValue. It is significant and can notIgnored.

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On this meter stick, the closest lines are 1 millimeter or 0.001 meter apart.

source

What’s the calibration?

Meter Stick

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source

What’s the calibration? 0.1 gram

Triple beam balance

What’s the reading? 373.35 g

What can we estimate to? 0.01 gram

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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 0.1 mlml

source

21.35 ml

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Now Let’s look at at a set of experimental B.P. Data collected by two students:

Student 1 Student 276.5 deg C 78.0 deg C76.1 78.476.6 77.976.9 78.2

76.5 AVG 78.1 AVG

The Accepted B.P. for this unk. is 77.2 deg C.

Which set of data is more precise & which setOf data is more accurate?

PERCENT ERRORPERCENT ERROR

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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

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Student 1: 76.5 - 77.2 x 100. = - 0.907% Error 77.2

Student 2: 78.1 - 77.2 x 100. = 1.17% Error 77.2

NOTE: ONLY THE SIZE OF THE ERROR ISIMPORTANT. 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 valueIs 77.2 what is her experimental error?

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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/cm3) or grams per milliliter (g/mL).

d = m / V

Remember … 1 cm3 = 1 milliliter

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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/v D must decrease. Why?

- SO DENSITY DEC. WITH INC. TEMPERATURE for SOLIDS, LIQUIDS OR GAS

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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

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Water is peculiar in that it’s volume increases as it goes from liquidAt 4 deg To solid at zero. This is opposite to how most materials behave.

D = M/V

As V increasesD decreases

So ice floats onwater

DENSITY

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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 mv2)

  - 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!

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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 273.15

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 onthe Centigrade and Kelvin scale

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Conversion formulas

How can we convert from one temperature scale to another?

K = C + 273 (more precisely 273.15)

C = K – 273

Know These !