science Flashcards
(25 cards)
What is a pure substance?
A pure substance contains only one type of particle. It is not mixed with anything else.
What is an impure substance?
An impure substance contains a mixture of different substances or particles.
How can you tell if a substance is pure using a temperature-time graph?
A pure substance has a sharp, flat melting point. An impure substance has a melting point that changes gradually.
Give 2 examples of pure substances.
Distilled water and oxygen.
They only have one type of particle.
Give 2 examples of impure substances and explain why.
Orange juice: contains pulp, sugar, vitamins. Sea water: contains water, salt, and other minerals.
Why is sodium chloride (salt) safe, but not sodium or chlorine on their own?
Sodium is a reactive metal and chlorine is poisonous. When combined, they form sodium chloride (NaCl), a safe compound.
Why do vaccine companies use pure water?
To make sure there are no extra substances that could react badly or cause side effects.
What is the difference between a pure substance and a mixture?
A pure substance has only one kind of particle. A mixture has more than one type mixed together.
What is a mixture?
A mixture is made of two or more substances that are not chemically joined. They can be elements, compounds, or both.
What is a compound?
A compound is a substance made from two or more elements chemically joined in a fixed ratio.
How are the substances in a mixture different from a compound?
In mixtures: substances keep their own properties. In compounds: the properties are different from the original elements.
Is it easy to separate a mixture or a compound?
Mixtures: yes, easy to separate. Compounds: no, chemical reaction needed to break them apart.
Can you change the amount of each substance in a mixture or a compound?
Mixture: yes, amounts can vary. Compound: no, fixed ratio.
Give one example of a mixture and one example of a compound.
Mixture: iron and sulfur. Compound: iron sulfide (FeS).
Why isn’t frozen fruit salad a compound?
Even if frozen or crushed, the substances in it are not chemically joined, so it’s still a mixture.
Why are mixtures like paint or vaccines useful?
They mix useful substances (like pigments or stabilizers) while keeping their individual properties.
What is an ore?
An ore is a naturally occurring rock that contains enough metal or metal compound to make it worth extracting.
Where are metals usually found?
Metals are found in the Earth’s crust, usually joined to other elements in compounds, often as metal oxides.
What are minerals?
Minerals are natural solid substances found in the ground. They are often used to get metals.
What is the process of extracting a metal?
Extraction means separating the metal from the compounds it’s mixed with.
What method is used to extract metals more reactive than carbon?
Electrolysis is used (e.g. Aluminium).
What method is used to extract metals less reactive than carbon?
They are extracted by heating with carbon (e.g. Iron, Zinc).
What method is used to extract unreactive metals like gold?
They are found in native (pure) form and separated using physical methods.
What are the two steps to extract iron from its ore?
Separate iron oxide from other compounds. Heat with carbon (charcoal) to extract the metal.
