Introduction to Chemistry Chapter 1 Introduction to Chemistry

1.1 The Scope of Chemistry What is chemistry? is the study of the composition of matter and the changes that matter undergoes. Matter – anything that has mass and volume Volume – amount of space an object occupies Mass – amount of matter an object contains Weight – pull of gravity on an object (proportional to mass and force of gravity).

1.1 The Scope of Chemistry Branches of Chemistry Organic chemistry – study of carbon containing chemicals Inorganic chemistry – study of matter that does not contain organic chemicals Physical chemistry – the area that deals with the mechanism, rate, and energy transfer that occurs when matter undergoes change Analytical chemistry – study that focuses on the composition of matter Biochemistry – study of matter and processes of living organisms.

1.1 The Scope of Chemistry Pure Chemistry: Applied Chemistry: The pursuit of chemical knowledge for its own sake. Study to understand Applied Chemistry: Research that is directed toward a practical goal or application. Study to use Alexander Fleming used pure then applied chemistry to understand mold growth.

1.2 Chemistry and You Technology: The means by which a society provides its members with those things needed and desired. Examples of modern research in chemistry technology: benefit the environment conserve and produce energy improve human life expand our knowledge of the universe.

1.3 Thinking Like a Scientist Scientific Method Logical, systematic approach used to understand the world around us. A HYPOTHESIS CAN NOT BE PROVEN CORRECT! IT CAN ONLY BE PROVEN WRONG! Observation Hypothesis Experiment Conclusion (theory or law)

1.3 Thinking Like a Scientist Understanding the parts Observations: using senses to obtain data Qualitative data – descriptive, nonnumeric information. Color, odor, texture, or “hot” and “cold” Quantitative data – definite numerical information. 38 °C, 24.5 m , or 4.1 × 1015 Hz

1.3 Thinking Like a Scientist Hypothesis Proposed explanation for an observation or “educated guess” Written as an “If and then” statement Experiment Procedure used to test hypothesis Independent variable – the variable that will be changed; what the scientist controls/manipulates Dependent variable – the variable that is observed; responds to independent variable Constants – the other factors that are not allowed to change. Control – standard used for comparison

1.3 Thinking Like a Scientist Class Example 1: Example: An experiment is designed to test the hypothesis that “If table salt is placed in hot water, then it will dissolve faster in hot water than in room temperature water.” Hypothesis:_______________________ Independent variable: Dependent variable: Constants: Control: temperature rate of dissolving amount of salt, water, and stirring rate room temp water dissolves

Class Example 2: Class Example 2: Sandra thought that all colas tasted the same, but her friends seemed to have favorite brands. She decided to see if people could really taste the difference between brands of cola. At the local grocery store she purchased 2 liter bottles of Coke, Pepsi, and a generic brand sold there. She got 10 of her friends together at her house for the test. Each person was asked which cola they preferred and then given three unmarked cups of cola to taste. Each cup contained 50 mL of cola. Sandra recorded how many of the people actually picked the cola they said was their favorite.

Class Example 2: Independent variable:_______________ Constants:____________________ Control:______________________ brand choice of favorite same friends, 50mL cola & unmarked cups Generic brand

1.3 Thinking Like a Scientist Conclusion Theory – tested explanation for a broad set of observations explanation of WHY something occurs. Ex: Einstein’s theory of relativity, Atomic theory, Kinetic theory, and Quantum theory Model – visual, verbal or mathematical explanation that needs extensive testing to become a “theory”. Law – a concise statement that summarizes the results of many observations and experiments summary of WHAT will occur. Newton’s First Law (gravity) and Law of Conservation of mass based on what has already happened

1.3 Thinking Like a Scientist: The Scientific Method Experiments An experiment can lead to observations that support or disprove a hypothesis. Theory A theory is tested by more experiments and modified if necessary. Hypothesis A hypothesis may be revised based on experimental data. Observations Scientific Law A scientific law summarizes the results of many observations and experiments.

Graphing Using data to create a graph can help to reveal a pattern if one exists. A graph is a visual display of data.

Circle Graph A circle graph is sometimes called a pie chart because it is divided into wedges like a pie or pizza. A circle graph is useful for showing parts of a fixed whole. The parts are usually labeled as percents with the circle as a whole representing 100%.

Bar Graph A bar graph often is used to show how a quantity varies with factors such as time, location, or temperature. In those cases, the quantity being measured appears on the vertical axis (y-axis). The independent variable appears on the horizontal axis (x-axis). The relative heights of the bars show how the quantity varies.

Line Graph In chemistry, most graphs that you create and interpret will be line graphs. The points on a line graph represent the intersection of data for two variables. The dependent variable is plotted on the y-axis and the independent variable on the x-axis. The independent variable is the variable that a scientist deliberately changes during an experiment.

Line Graph Sometimes points are scattered, the line cannot pass through all the data points. The line must be drawn so that about as many points fall above the line as fall below it. This line is called a best fit line.

Line Graph If the best fit line is straight, there is a linear relationship between the variables and the variables are directly related. This relationship can be further described by the steepness, or slope, of the line. If the line rises to the right, the slope is positive. A positive slope indicates that the dependent variable increases as the independent variable increases.

Line Graph If the line sinks to the right, the slope is negative. A negative slope indicates that the dependent variable decreases as the independent variable increases.

Line Graph Either way, the slope of the graph is constant. You can use the data points to calculate the slope of the line. The slope is the change in y divided by the change in x.

Interpreting Graphs When points on a line graph are connected, the data is considered continuous. You can read data from a graph that falls between measured points. This process is called interpolation.

Interpreting Graphs You can extend the line beyond the plotted points and estimate values for the variables. This process is called extrapolation. Why might extrapolation be less reliable than interpolation? The trend might change!