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– Scientists have grouped properties into two categories: physical properties and chemical properties.
– The properties you just described when talking about the Johnson uniform are what scientists call “physical properties.” Physical properties are characteristics that describe matter based on your 5 senses: sight, smell, sound, touch, and taste.
– Let’s examine a few common physical properties:
- Colour – Example: hydrogen gas is invisible, sulfur is bright yellow, and silver is gray.
- Texture – this is how matter feels. Example: smooth versus coarse.
- Odour – this is how matter smells. Carbon monoxide (CO) gas is odourless, sulfur smells like rotten eggs, and methane is the common chemical when animal’s “pass gas.” When smelling a chemical for the first time, scientists use a technique called “wafting.” In this procedure, you wave the air above the substance towards your nose. This technique is useful because if the chemical has a very strong odour, wafting allows you to detect the odour without becoming overwhelmed with it.
- Lustre – This describes how shiny a chemical is. For example, depending on how carbon (C) is formed, it can be shiny or dull. The carbon in your pencil “leads” and in coal is very dull. Carbon in diamonds is very shiny. Most metals have a high lustre.
- Clarity – This describes how well you can see through a chemical. Chemicals can be clear (ex. Pure water), cloudy (ex. Vegetable oils), or opaque (ex. Milk). Opaque means that you cannot see through the chemical.
- Taste – The four major tastes are sour, salty, sweet, and bitter. Acids usually taste very sweet (ex. Citric acid in fruits and hard candies)
NEVER EVER taste an unknown chemical!
- State – Matter exists in 3 states: solid, liquid and gas. To get from one state to another, a change in temperature must occur.
- Density – This is how much matter exists in a certain space. It is a ratio of the mass of a chemical compared to its volume (how much space it takes up). Each element has a different density, with lead being the densest element (it weighs the most for the space it takes up). This means that a piece of lead the size of an ice cube would weigh much more than a piece of carbon the size of an ice cube.
- Hardness – This property describes how a solid resists being scratched or dented. For example, glass is a hard substance, but not hard enough that it can’t be scratched. Diamonds are the hardest substance on Earth. The only thing that can scratch a diamond is another diamond.
- Melting Point – This is the temperature at which a solid becomes a liquid. For example, the melting point of water is 0oC, while the melting point for copper is 1084oC (this is why it’s easy to get liquid water, but not liquid copper!). Every element has a different melting point.
- Boiling Point – This is the temperature at which a liquid becomes a gas. For example, the boiling point of water is 100oC, while the boiling point of nitrogen is –196oC (this is why at room temperature (23oC), water is a liquid and nitrogen is a gas). Every element has a different boiling point.
- Solubility – This property measures how easy it is for a chemical to dissolve in water. When a chemical is placed into water, the chemical is called the solute and the water is called the solvent. Solutes are always placed into solvents.
- Viscosity – This property measures how easily a liquid can flow. If a chemical has a high viscosity, it means that it flows very slowly, like honey or molasses. Chemicals with low viscosities flow very quickly, for example, water and alcohol.
– A chemical property describes how a substance behaves and what it does when it reacts (combines) with another chemical.
– Let’s examine a few common chemical properties:
- Combustibility – This property describes how easily a chemical can catch on fire. For example, it is very difficult to light gold on fire, but it is very easy to light gasoline on fire.
- Light Sensitivity – Some chemicals are very sensitive to light and actually change into a different substance when exposed to light. For example, hydrogen peroxide (used as a disinfectant, you can buy it at any drug store) is sensitive to light. It is sold in a dark brown bottle so it won’t react with the light.