CHAPTER1: CHEMICAL FOUNDATIONS

Science

Science is a process for understanding nature and its changes.

Chemistry

The branch of science concerned with the composition, properties, and reactions of substances.

Chemistry is around you all the time.

SCIENTIFIC METHOD

Scientific method is a framework for gaining and organizing knowledge. The general method that applies for most sciences is given below.

Steps in the scientific method

1. Observations Observations (collecting data) are two type:- Qualitative: Description, not a measurement.

(Example: color, strength, etc)- Quantitative: Measurement

(Example: weight)

2. Formulating hypotheses- Possible explanation (make a guess) for the observation.

3. Performing experiments to test the hypothesis.- Gathering new information to decide whether the hypothesis is

valid.

A set of hypothesis (confirmed by experiments) that gives an explanation of some natural phenomenon is called theory.

If the theory can be applied to many different systems, it is called natural law.

A law summarizes what happens.

A theory (model) is an attempt to explain why it happens.

MEASUREMENT

Making observation is fundamental to all science.

A quantitative measurement (observation) consisting of 2 parts.

Part 1 – number,

Part 2 – scale (unit)

Eg: 20 grams, 5 liter

International System of measurement

Chemists around the world have agreed to a single system of scales that allows their work to be compared. This is called International System or SI. This is based on metric system.

The Fundamental SI Units

Physical Quantity Name Abbreviation

Mass kilogram kgLength meter mTime second sTemperature kelvin KElectric current Ampere AAmount of solute Mole MolLuminous intensity Candela cd

The prefixes used in SI system

The SI units are not always convenient. So, prefix is used to change the size of the unit.

Example. Mass of small gold earring = 0.000001 kg

Using too many zero is not convenient. So, we can use a prefix.

0.000001 kg = 1 milligram (milli is the prefix)

(1 kilogram = 1000 g; 1 gram = 1000milligram)

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Commonly used prefixes in SI system

Prefix MeaningExponential

Notiongiga 1,000,000,000 109

mega 1,000,000 106

Kilo 1,000 103

Hector 100 102

Deka 10 101

- 1 100

Deci 0.1 10-1

Centi 0.01 10-2

Milli 0.001 10-3

Micro 0.000001 10-6

nano 0.000000001 10-9

Uncertainty in measurement

Measurement always has some degree of uncertainty.

Certain digits: Digits which are same during repeated measurements.

Uncertain digits: Digit which is changing during repeated measurements.

Measurements are represented as

“Certain digits + First uncertain digit”

Example.

Result of the measurement of volume (in buret) may be

20.15 or 20.16 or 20.17

20.1 is certain digits 0.05, 0.06, 0.07 are uncertain digits

We can write it as 20.16 ± 0.01

± 0.01 is called as uncertainty

Precision and accuracy

Accuracy: Agreement of a particular value with the true value.

Precision: Degree of agreement among several measurements of the same quality. It reflects the reproducibility of a given type of measurement.

Types of error in measurement

Random Error (Indeterminate Error) - measurement has an equal probability of being high or low.

Systematic Error (Determinate Error) - Occurs in the same direction each time (high or low), often resulting from poor technique or the equipment.

Exact weightRandom error in

measurementSystemic error in

measurement

100 gram

98 gram

99.8 gram

102 gram

110 gram

108 gram

111 gram

SIGNIFICANT FIGURES

Significant figures refer to the digits in a number that you believe are significant or relatively certain.

Rules for Counting Significant Figures

1. Nonzero integers always count as significant figures.Eg. 3456 has 4 significant figures.

2. Zeros- Leading zeros DO NOT count as significant figures.

Example: 0.0486 has only 3 significant figures.

- Captive zeros always count as significant figures.

Example: 16.07 has 4 sig figs.

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- Trailing zeros are significant only if the number contains a DECIMAL point (Be careful- this may be confusing!).

Example: 20354000 has 5 sig figs.

20354000. has 8 sig figs.

.002035400 has 7 sig figs.

3. Exact numbers. Exact numbers never limit the number of significant figures.

Example: Counting numbers (Example. 5 experiments, 6 cigarettes) Exact constants (Example. 1 inch = 2.54 cm, exactly)

Exercise 1.

How many significant figures in 103.351 X 102?

103.351 X 102 = 5 significant figures

(X102 do not count as significant figure)

Round off

In most of the calculations we need to round numbers to obtain the correct number of significant figures.

Rules:

1. First do the full calculation (to get final result) and then round off.2. If the digit to be removed

- Is less than 5, the preceding digit stays the same.Eg. 1.33 round to 1.3

- Is equal to or greater than 5, the preceding digit is increased by one (+1).Eg. 1.36 round to 1.4

Exercise 1. Round off 0.00034159 to 3 digits

3.42 X 10-4

Exercise 2. Round off 0.00034159 to 3 significant figures

0.000342

MATHEMATICAL OPERATIONS

Multiplication and Division: Number of significant figures in the result equals the number in the least precise measurement used in the calculation (the one with smallest number of significance).

Exercise 1.

6.38 X 2.0

(6.38 = 3 sig figs; 2.0 = 2 sig figs. So, the result should be 2 sig figs)

6.38 X 2.0 = 12.76

= 13 (2 sig figs )

Exercise 2.

23 / 275.15

(23 = 2 sig figs; 275.15 is 5 sig figs. So the result should be 2 sig figs)

23 / 275.15 = 0.0835908

= 0.084 (2 sig fig)

Addition and Subtraction: Number of decimals in the result equals the number of decimal places in the least precise measurement.

Exercise1. 6.8 + 11.934

(6.8 has 1 decimal, 11.934 has 3 decimalSo the result should have only 1 decimal)

6.8 + 11.934 = 18.734 = 18.7 (1 decimal)

Exercise 2.

0.355 + 105.1 - 100.5820 (0.355 has 3 decimal, 105.1 has 1 decimal, 100.5820 has 4 decimals

So the result should have only 1 decimal places)

0.355 + 105.1 - 100.5820 = 4.8730 = 4.9 (1 decimal)

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Combination of addition/subtraction and multiplication/division

1. Perform full calculation (use calculator) to get the result.2. Round-off in the intermediate steps to decide the correct number of

significant figures.3. Express the result in correct number of significance.

Exercise 1. (24.6681 X 2.38) + 332.58

Calculation(24.6681 X 2.38) + 332.58 = 391.29007

Deciding correct number of significant figures:

(24.6681 X 2.38) + 332.58 = 58.7 + 33.58

– Answer should have only one decimal.

Answer = 391.3

Exercise 2. (85.3 - 21.489) / 332.58

Calculation(85.3 - 21.489) / 332.58 = 10815.423

Deciding correct number of significant figures:(85.3 - 21.489) / 332.58 = 63.8 / 0.0059

– Answer should have 2 significant figures.

Answer = 1.1 x 104

Exercise 3. [(28.7 x 105) / 48.533] + 144.99

Calculation[(28.7 x 105) / 48.533] + 144.99 = 592800

Deciding correct number of significant figures:[(28.7 x 105) / 48.533] + 144.99 = (2870000 / 48.533) + 144.99

= (5.91 x 104) + 144.99

– Answer should have only 2 decimals.

Answer = 5.93 x 104

CONVERTING FROM ONE UNIT TO ANOTHER

Proper use of “unit factors” leads to proper units in your answer.

Dimensional analysis

There are different scales for dimension such as meter, Km, yard and mile.

Exercise 1. Convert 10 km to miles

(1 km = 1000 m; 1m = 1.094 yards; 1760 yards= 1 mile)

Convert km → m → yard → mile

10 km X (1000 m / 1 km) X (1.094 yards / 1 m) X (1 mile/ 1760 yard)

= 6.22 miles

Exercise 2. Convert the gas mileage 15 km/L to miles/gallon

(1 km = 1000 m; 1m = 1.094 yards; 1760 yards= 1 mile 1 L = 1.06 qt; 4 qt = 1 gal)

First Convert km → m → yard → mile, and then convert L → qt → gal

15 km/L X (1000 m / 1 km) X (1.094 yards / 1 m) X (1 mile/ 1760 yard) X (1 L/1.06 qt) X (4 qt/1 gal)

= 35 miles/gallon

Temperature Analysis

There are three major temperature scales

1) Celsius scale = °C2) Kelvin scale = K3) Fahrenheit scale = °F

Conversion of temperature

TK = TC + 273.15

TC = TK - 273.15

TF = TC X (9/5) + 32

TC = (TF – 32) X (5/9)

Where, TK = Temperature in Kelvin scale

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TC = Temperature in Celsius scale

TF = Temperature in Fahrenheit scale

Exercise 1.

Boiling point of water is 100 °C. Convert it to Fahrenheit and Kelvin scales.

TC = 100 °C

TK = TC + 273.15 = 100 + 273.15 = 373.15 °C

TF = TC X (9/5) + 32 = 100 X (9/5) + 32 = 180 + 32 = 212 °F

Exercise 2.

Normal body temperature is 98.6 F. Convert it to Celsius and Kelvin scales.

TF = 98.6 °F

TC = (TF – 32) X (5/9) = (98.6 – 32) X (5/9) = 66 X (5/9) = 37 °C

TK = TC + 273.15 = 37 + 273.15 = 310.15 = 310.2 K

DENSITY

Density is the mass of substance per unit volume of the substance.

Density = Mass/volume

CLASSIFICATION OF MATTER

Matter: Anything occupying space and having mass.

Solid Liquid Gas

Three States of Matter (based on physical form)

1) Solid: Rigid - fixed volume and shape.2) Liquid: Definite volume but assumes the shape of its container.3) Gas: No fixed volume or shape - assumes the shape of its container.

A second way to classify matter is based on its composition.

Most matter around is a Mixture of pure substances.

Mixture can be divided into 2 groups

1) Homogenous mixture: It is very hard to distinguish the individual parts (eg. Solutions).

2) Homogenous mixture: it has visibly distinguishable parts.

A mixture can be separated into individual pure substances. There are various physical methods that can be used to separate mixtures. These include distillation, filtration, and chromatography. This separation is a physical change (NOT a chemical change).

A pure substance is one with constant composition. It may be an element or a compound.

Compound is composed of different elements, and may be broke down into elements by chemical methods.

Elements cannot be decomposed to simpler compounds by either physical or chemical processes, and can only be broken down by nuclear interactions.

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Matter

Mixers Pure substances

Homogenous mixures

Heterogenous mixures

Element Complex

Atoms

Various composition?NoYes

Visibly distinguishable?

YesNo

Physical methods

Various atoms?

YesNo

Chemical methods

CHAPTER 1: MODEL QUESTIONS & ANSWERS

Note: The correct answer was indicated by underline

1) How many significant figures in 0.003840?

a) 7 b) 4 c) 3 d) 6

Calculate the significant figures for the following numbers.

Number Sig figs. Number Sig figs.

6.07 × 10-15 3 3.0 × 102 2

17.00 4 301 3

8 X 108 1 300 1

463.8052 7 300. 3

2) Round off 17.9915 to 5 digits.

a) 17.992 b) 17.9 c) 18.0 d) 17.991

Round off each of the following numbers to the indicated digits.

Round off the following numbers Answer

0.084 to 2 digits 8.4 X 10-2

0.00034159 to 3 digits 3.42 X 10-4

103.351 X 102 to 4 digits 1.034 X 104

3.365 X 105 to 3 digits 3.37 X 105

3) Round off 17.9915 to five significant figures.

17.992

Round off each of the following numbers to the indicated significant figures.

Round off the following numbers Answer

0.000341591 to 3 significant figures 3.42 X 10-4

0.0746 to 4 significant figures 0.07460

3065 to 2 significant figures 3.1 X 103

4) Calculate (0.102 X 0.0821 X 243)/1.01 and express the result to the correct number of significant figures.

(0.102 X 0.0821 X 243) / 1.01 = 2.0147827 = 2.01 (3 sig figs)

5) Calculate 2.01 x 102 + 3.014 x 103 and express the result to the correct number of significant figures.

2.01 x 102 + 3.014 x 103 (Answer should have only 2 decimal)

= 201 + 3014 = 3215 = 3.22 x 103

Also Perform the following calculations.

Calculation Result Answer with correct significant figures

212.2 + 26.7 + 402.09 640.99 641.0 (1 decimal)

1.0028 + 0.221 + 0.10337 1.32717 1.327 (3 decimal)

52.331 + 26.01 – 0.9981 77.3429 77.34 (2 decimal)

7.255 - 6.8350 0.4200 0.420 (3 decimal)

6) Calculate (512 / 986.7) + 5.44 and express the result to the correct number of significant figures.

Step 1: Calculation

(512 / 986.7) + 5.44 = 5.9589013

Step 2: Deciding correct number of significant figures:

(512 / 986.7) + 5.44 = 0.519 + 5.44

– Answer should have only 2 decimals.

Step 3: Answer = 5.96

Also perform the following calculations.

Calculation Result Answer

(2.526/3.1) + (0.470/0.623) + (80.705/0.4326)

188.12727 188.1 (1 decimal)

(6.404X2.91) / (18.7-17.1) 11.647275 12 (2 Sig fig)

(9.5 + 4.1 + 2.8 + 3.175) / 4 4.89375 5 (1 Sig fig)

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7) Convert the gas mileage 10 km/L to miles/gallon

(1 km = 1000 m; 1m = 1.094 yards; 1760 yards= 1 mile; 1 L = 1.06 qt; 4 qt = 1 gal)

10 km/L X (1000 m / 1 km) X (1.094 yards / 1 m) X (1 mile/ 1760 yard) X (1 L/1.06 qt) X (4 qt/1 gal)

= 23.5 miles/gallon

8) Calculate the number of minutes in a month: 24 hours per day, 60 minutes per hour, 7 days per week, and 4 weeks per month.

Convert: month → week → days → hours → minutes

1 month X (4 weeks/month) X (7 days/week) X (24 hrs/day) X (60 min/hr)

1 month = 40320 mins

9) Convert -25° C temperature to Kelvin and Fahrenheit scales.

TC = -25° C

TK = TC + 273.15 = -25 + 273.15 = 248.15

TF = TC X (9/5) + 32 = -25 X (9/5) + 32 = -45 + 32 = -13 °F

10) Which one of the following has fixed volume and variable shape?

a) Gas b) Liquid c) Solid d) All the above

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