C3 Pure and Impure Substances Flashcards
Define element
A substance made of only one type of atom.
Define (chemical) compound
Substance made of more than one type of atom chemically bonded together.
Define (chemical) molecule
Two or more atoms, chemically bonded into a single particle.
Does a molecule have to be a compound?
No, a molecule can be an element made of more than one of the same type of atom chemically bonded together into a single particle.
Define (chemically) pure
When a substance is made of only one element or compound.
Define (chemically) impure
When a substance is made of more than one element or compound, or a mixture of elements and compounds.
What is a mixture?
An impure substance that can be separated by physical (not chemical) processes.
Is spring water pure? Explain your answer.
No. Spring water contains minerals, as well as water molecules which are not chemically bonded.
Is air pure? Explain your answer.
No. Air contains a mixture of elements and compounds in their gaseous state which are not chemically bonded.
State one similarity and one difference between boiling and evaporation?
Similarity: both a state change from liquid to gas
Difference: Evaporation can occur at any temperature, boiling occurs at the boiling point of the substance.
Define dissolve
When a substance is added to a solvent (liquid) and its particles spread out evenly within the liquid.
Define solute
A solid or gas that dissolves in a solvent.
Define solvent
A liquid that dissolves a solute
Define solution
A mixture made when a solute dissolves in a solvent.
Define solubility
The mass of a solute that will dissolve in a given volume of solvent
Define insoluble
A substance that does not dissolve in a liquid.
Define soluble
A substance that does dissolve in a liquid (solvent).
What is a saturated solution?
A solution where no more solute will dissolve in the solvent.
Generally, what is the effect of increasing the temperature on solubility?
The greater the temperature, the greater the solubility
What piece of equipment could be used to separate marbles from sand, and what physical property does it separate them based on?
Sieve. Based on the size of the object.
What physical property does filtration separate substances based on?
Size of particles
What word could be used to describe the solubility of sand in water?
Insoluble
What is the name of the substance left in the filter (paper) after filtration?
Residue
What is the name of the substance that passes through the filter (paper)?
Filtrate
What types of substances are most commonly separated by filtration in chemistry?
Insoluble solids from liquids
What types of substances are most commonly separated by evaporation in chemistry?
Soluble solids from liquids
What is crystallisation?
Slow evaporation that allows crystals to form.
What physical property does chromatography separate substances based on?
Solubility
What is chromatography used to separate?
Pigments (colours) in a solution.
Which part of the simple chromatography set-up is considered the stationary phase?
The paper.
Which part of the set-up above is considered the mobile phase?
The solution moving up the paper.
What formula can be used to calculate the retention factor (Rf) of the pigment?
Rf = Distance moved by pigment / Distance moved by solvent
Calculate the Rf value of red pigment which has moved 2cm when the solvent has moved 10cm on a chromatogram.
Rf= 2/10 = 0.2
Calculate the Rf value of the purple pigment which has moved 6cm when the solvent has moved 10cm on a chromatogram.
Rf= 6/10 = 0.6
What is the piece of paper with separated pigments called, once chromatography is complete?
Chromatogram
What process can be used to separate two liquids based on their boiling points?`
Distillation
What is the state change that occurs in the round bottomed flask during simple distillation?
Boiling or evaporation (liquid to gas)
What is the state change that occurs in the condenser during simple distillation?
Condensing (gas to liquid)
What does desalination mean?
To remove salt from salt water (sea water)
Why do we not use desalination to produce drinking water in the UK?
Very energy intensive. No need as we have a good supply of clean drinking water.
Fractional distillation separates out a range of different chemicals based on their…
Boiling points.
Give two mixtures that are commonly separated using fractional distillation.
Air and crude oil
What scale is used to represent how acidic or alkaline something is?
pH scale
What is the pH of a neutral substance?
7
What is the pH of an acidic substance?
Less than 7
What is the pH of an alkali substance?
More than 7
How could you describe a substance of pH 8
(Weak) Alkali
How could you describe a substance of pH 2
(Strong) Acid
How could you describe a substance of pH 5
(Weak) Acid
How could you describe a substance of pH 14
(Strong) Alkali
What is the standard word equation for a reaction between an acid and an alkali?
Acid + Alkali → Salt + Water
What type of salts are formed by hydrochloric acid?
Chloride salts
What type of salts are formed by sulfuric acid?
Sulfate salts
What type of salts are formed by nitric acid?
Nitrate salts
Give the word equation for the reaction between copper oxide and sulphuric acid
Copper oxide + sulfuric acid → copper sulphate + water
Give the word equation for the reaction between sodium hydroxide and hydrochloric acid
sodium hydroxide + hydrochloric acid → sodium chloride + water
Give the word equation for the reaction between potassium hydroxide and nitric acid
potassium hydroxide + nitric acid → potassium nitrate + water
What is the name for a reaction where the pH moves towards 7.
Neutralisation
What colour of universal indicator is usually associated with acidic substances.
Red
What colour of universal indicator is usually associated with alkaline substances.
Purple / Blue
What colour of universal indicator is usually associated with neutral substances.
Green
