click below
click below
Normal Size Small Size show me how
CC1,2F
GCSE Combined Science Chemistry
Question | Answer |
---|---|
Define mixture | A substance made of more than one thing not chemically bonded together |
What are the 3 states of matter? | Solid, liquid and gas |
What is the change from a solid to a liquid called? | Solid à liquid – melting |
If the temperature is above the melting point of a substance but below the boiling point of a substance what state will it be in? | Liquid |
If the temperature is below the melting point of a substance and below the boiling point of a substance what state will it be in? | Solid |
If the temperature is above the melting point of a substance and above the boiling point of a substance what state will it be in? | Gas |
What is the change from a liquid to a gas called? | Liquid à gas – evaporation |
What is the change from a gas to a liquid called? | gas à liquid – condensation |
What is the change from a liquid to a solid called? | liquid à solid – freezing |
Describe the arrangement of the particles in a solid | particles closely packed, in a regular arrangement |
Describe the arrangement of the particles in a liquid | particles closely packed, but in a random arrangement |
Describe the arrangement of the particles in a gas | particles spaced far apart in a random arrangement |
A substance has a melting point of 25 oC and a boiling point of 235 oC. What state is it at 5oC? | Solid |
A substance has a melting point of -125 oC and a boiling point of -35 oC. What state is it at 15oC? | Gas |
A substance has a melting point of -25 oC and a boiling point of 35 oC. What state is it at 25oC? | liquid |
Describe how the particles change in arrangement when a solid turns into a liquid | Forces between particles weaken and they move more freely. The particles are not arranged in order |
Describe how the particles change in arrangement when a liquid turns into a solid | Forces between particles weaken and they move freely. They are spaced far apart |
Describe how the particles change in arrangement when a gas turns into a liquid | Forces strengthen, particles move closer together |
Describe how the particles change in arrangement when a liquid turns into a gas | Forces strengthen, particles move close together in ordered rows |
Describe the arrangement of particles in a gas. | Random and far apart |
Describe the arrangements of particles in a liquid | Random and close together |
Describe the arrangements of particles in a solid | Regular and close together. |
Describe the movement of particles in a gas. | Fast in all directions |
Describe the movement of particles in a liquid | Move fast around each other |
Describe the movement of particles in a solid | Vibrate around fixed positions. |
What is the name in change of state from gas to liquid? | Condensation. |
State the meaning of sublimation | The change in state from solid to a gas |
How can you see from a cooling or heating curve that a pure substance is changing state? | The temperature does not change during a change of state of a pure substance. |
The boiling point of ethanol is 78oC the melting point of ethanol is -114oC. What state is ethanol at 90oC? What state is ethanol at -150oC? | Gas and Solid. |
Describe the movement of particles in a gas. | Fast in all directions |
Describe the movement of particles in a liquid | Move fast around each other |
Describe the movement of particles in a solid | Vibrate around fixed positions. |
What is the name in change of state from liquid to solid? | Freezing |
State the meaning of evaporation | The change in state from liquid to gas |
The boiling point of a substance is -80oC the melting point of ethanol is -200oC. What state is ethanol at -85oC? What state is ethanol at -250oC? | Liquid and Solid. |
Define an element | A substance made of only one type of atom. |
Define a compound | A substance made from two or more different elements bonded together. |
Define a mixture | A substance made of two or more substances (elements or compounds) mixed but not bonded together. |
What types of mixtures can be separated filtration? | A mixture of a liquid and a solid. |
Define a solution. | A mixture of a solute dissolved in a solvent. |
What are the risks of crystallisation and how do you reduce them? | As the solvent boils away the hot solution can spit so wear safety goggles to protect your eys. |
State the five steps of the chromatography method | "1. Draw pencil line on paper 2. Place sample spot on line, 3. Place paper in solvent, with solvent below pencil line, 4. Allow solvent to soak up the paper 5. Stop when solvent near top, and mark how far it gets. |
" What are the three uses of chromatography | To tell between pure and impure substances, To identify substances by comparison with known ones, To identify substances by calculating Rf. |
What is chromatography? | A process to separate the constituents of a mixture |
In paper chromatography, what is the stationary phase and what is the mobile phase | Paper is stationary, solvent (usually water or ethanol) is mobile |
How can chromatography show the difference between pure and impure substances? | Pure ones will not separate into a number of spots |
How is the Rf value calculated? | distance moved by spot/distance moved by solvent |
What does a substance's Rf value depend on? | How soluble it is in the solvent |
In chromatography, why must the substances be placed on a pencil line? | Pencil will not dissolve in the solvent |
In chromatography why must the solvent height be lower than the pencil line? | So that the substances do not dissolve into the solvent off the paper |
How is the melting point of a pure substance different from that of an impure substance? | Pure substance has one specific melting point. Impure substance has a melting range. |
What is simple distillation used to separate? | A liquid from a solid |
What is fractional distillation used to separate? | Two liquids with different boiling points. |
What is filtration used to separate? | An insoluble solid from a liquid |
What is crystallisation? | Forming crystals of a soluble solid from a solution. |
How can sea water be made potable? | By distillation |
What are the stages used to make water potable. | Sedimentation, filtration and chlorination |
What is a pure substance? | A substance made of one type of atom or molecule only. |
How would you separate water from salt water? | Simple distillation |
How would you separate salt from salt water? | Crystallisation |
How is the melting point of a mixture different from a pure substance? | A pure substance has a single melting temperature, a mixture has a range of melting points. |
What is distillation? | A method to collect a pure liquid from a solution. |
What is the role of a condenser in a distillation experiment? | It condenses hot gases back into liquids by cooling them down. |
If a mixture of alcohol boiling point 78OC and water boiling point 100oC undergoes fractional distillation, which will boil first? | Alcohol |
Why will be certain that the first liquid being collected is alcohol, and water is not being collected as well? | The temperature will stay at 78oC until all the alcohol has boiled |
Define potable water. | Water that is safe to drink. |
Define desalination . | Producing pure water from sea water |
Why is desalination not more widely used to produce drinking water around the world | It takes a lot of energy so is expensive. |
Why do chemists carry out tests with pure water not tap water? | Dissolved substances in tap water could interfere with the results. |
What are the three stages of water treatment in the UK | Sedimentation, Filtration, Addition of Chlorine |
Why is chlorine added to drinking water? | To kill bacteria. |