Якісна та кількісна інформація

Quality and Quantity

You may have heard the phrase, "Quality is better than quantity", but when it comes to measuring data the phrase doesn't always apply. In chemistry, data can be measured in many ways, but it is broken down into two types:

• Qualitative data - this data describes qualities of a material, usually without values. It describes properties that can be judged with human senses.

• Quantitative data - this type of data describes qualities of a material which are measurable and expressed with values. Often these properties require a type of scientific measurement and result in numerical data.

Both qualitative and quantitative data, coupled with statistical analysis, is integral to understanding datasets and developing a conclusion.

Everyday Example

Let's consider a bunch of apples! We can gather qualitative data by examining the apples.

Qualitative data:

• Color: The color of the apples are red, yellow, and green on the outside. When cut, the apple flesh is white. After sitting in air, the apple skin browns.

• Smell: The apples have an earthy smell, but when cut they smell fruity.

• Texture: The apples on the outside are smooth and waxy. Inside the apples are slightly gritty.

• Taste: The red apples are sweet, the green ones are tart, and the yellow ones are sweet and tart.

Quantitative data:

• Quantity: There are 8 apples in total: 3 yellow, 3 green, and 2 red.

• Mass: The mass of the apples can be found using a scale or balance.

• Chemical composition: Analytical chemists can determine the atoms and molecules that make up the apple. How? They use specialized instruments and techniques. The amount of each compound in a known portion of an apple can be used to determine the amount in the whole apple. As the cut apples brown, the chemical composition changes. The apple flesh undergoes oxidation with the air. The color and oxidation state are related!

• Absorbance: The skin of the apples are different colors. The pigments in the skin can be isolated from the apples. These pigment compounds can be studied to determine their composition and absorbance. The absorbance will be related to the color of the apple.

Example in Chemistry

When you run a chemical experiment in chemistry, often both types of data are used to gain information. Let's start with a chemical reaction! Two solutions are made:

• Silver nitrate ($AgNO_3$) in water

• Calcium chloride ($CaCl_2$) in water

The solutions are mixed together. As they mix, a white solid forms and precipitates out of the solution! This indicates a chemical reaction might be occurring.

So far, we are able to gain some qualitative data:

• The two initial solids are white

• The initial solutions are both clear, colorless liquids.

• After the solutions mix, a white precipitate forms in a clear liquid

• There's no smell from any part of the reaction

Note that there are no observations about taste. It would be unsafe to taste chemicals which are not food or food safe.

So far we need more information and data to get an idea of what is going on. Let's try writing out a balanced chemical equation: $$2AgNO_3(aq)\ +\ CaCl_2(aq)\ \rightarrow\ Ca(NO_3)_{2}(aq)\ + 2AgCl(s)$$ We know that silver nitrate and calcium chloride dissolve in water from observation, but this is also supported by solubility rules. If the reaction undergoes a double-replacement reaction, calcium nitrate and silver chloride will form. Based on solubility rules, silver chloride is not soluble in water. So, it's likely our precipitate.

The solid can be filtered from the solution. To confirm a reaction has taken place, we can gather quantitative data:

• Melting point

• Mass

• Density

This data can be compared to known values for silver chloride to confirm identity.

Qualitative vs. Quantitative Data

The data collection methods, including physical measurements and case studies, distinguishes qualitative and quantitative data. Research methods can include both qualitative and quantitative data or just one. We will learn more about scales of measurement later.

Qualitative Data:

• Data based on observations: what did you see during the experiment? Did the solution smell like anything? Did the mixture get hot during the reaction?

• A common experimental design that relies on qualitative data is focus groups. Focus groups are in depth interviews where scientists ask questions about a certain subject to groups of people and analyze the answers using qualitative data analysis.

Quantitative Data:

• Data based on numbers: What was the temperature of the mixture? How much did that solid weigh? How many bacterial colonies are on the agar plate?

(Video) Qualitative and Quantitative

by The Organic Chemistry Tutor

This video will teach you the difference between quantitative and qualitative data, all just in six minutes. You'll also learn about discrete and continuous measurements and get a chance to practice classifying some data at the end.