States of matter

How are the particles in a solid arranged? What are its properties?

Particles have strong forces of attraction so are very close together, arranged in a regular pattern and vibrate about a fixed position.

Fixed shape, fixed volume, can't be compressed.

High density

How are the particles in a liquid arranged? What are its properties?

Particles have weaker forces of attraction so are still touching and close together, randomly arranged but are able to slide past each other.

Fixed volume but no fixed shape, can't be compressed, medium density.

How are the particles in a gas arranged? What are its properties?

Particles have almost no forces of attraction (very weak) (intermolecular forces) forces of attraction so are far apart, randomly arranged and can move quickly and freely in all directions in straight lines and therefore can collide with each other.

No fixed shape or volume, can be compressed and have a low density.

How can interconversions between states of matter change?

Matter usually changes state when you add or take away heat.

The amount of energy depends on the strength of the forces between particles (higher melting point = strong forces)

What is the difference between physical changes and chemical changes + examples

Physical: produce no new substances, reversible- changing states

Chemical: (involves the movement of electrons) involve the formation of new chemical elements or compounds, usually irreversible - chemical reactions.

What is the change in state from a solid to a liquid called? Explain the changes in movement and energy of the particles.

Melting.

When you heat up a solid particles (absorb the thermal energy and transformed into) gain kinetic energy so they vibrate faster (more) and eventually they have enough energy to overcome the forces of attraction holding the bonds together and can flow over each other, forming a liquid

Happens at a specific temp (melting point)

What is the change in state from a liquid to a gas called? 2 options. State the differences (I don't think I need to know) Explain the changes in movement and energy of the particles when boiling.

Evaporating

Occurs at the surface of liquids where some particles are moving faster than the average and others more slowly. Some fast moving particles have enough kinetic energy to overcome the forces of attraction (they break away to form a gas).

Larger SA and the warmer the liquid = quicker evaporation.

Occurs over a range of temperatures

Boiling

Thermal energy causes bubbles to form inside the liquid allowing for liquid particles to escape from the surface and within the liquid)

When you heat up a liquid particles gain kinetic energy so they move more and more quickly (seen as boiling) and eventually they have enough energy overcome the forces of attraction holding the bonds together.

Boiling happens at a specific temp (boiling point)

Explain what happens if the liquid is in a container

Particles in the gas will also be colliding with particles at the surface of the liquid. If they are moving slowly enough, they will be held by the tractive forces and become part of the liquid in a close container. Evaporation and condensation will both be occurring at the same time.

What is the change in state from a liquid to a solid called? Explain the changes in movement and energy of the particles.

Freezing or solidifying

If you cool a liquid, particles lose kinetic energy to flow, slowing down and eventually arrange themselves into a fixed, regular pattern.

Occurs at same temp as melting

What is the change in state from a gas to a liquid called? Explain the changes in movement and energy of the particles.

Condensing

Occurs over a range of temps

When a gas is cooled its particles lose energy and when they collide into each other they lack the energy to bounce away again, so instead, they group together to form a liquid

What is the change in state from a solid to a gas called?

Sublimation

What is the change in state from a gas to a solid called?

Deposition (deposing)

Solution + how is it measured? Example

Mixture (liquid) formed by a solute dissolving into a solvent and can't be separated unless a separation technique is used.

mol/dm^3 (number of particles per decimeter cube)

g/dm^3

Sea water

Solute + Example (1)

A substance that is dissolved in a solvent to form a solution

Salt in sea water

Solvent + Example (1)

A substance (usually a liquid) where the solute dissolves in

Water in sea water, nail polish

Soluble

A substance able to be dissolved

Saturated solution (2)

- A solution which contains as much dissolved solid as possible

- At a particular temperature

There must be some undissolved solute present

TRIPLE CONTENT: Solubility (definitions, units, factors that affect it)

The maximum mass of solute that dissolves in 100g of solvent at a particular temperature

g per 100g of solvent

Solubility changes with temperature. Generally the hotter the solvent, the more solute it dissolves.

Practical: investigating solubility of a solid in water at a specific temp

Describe a method

- Weigh an evaporating basin

- Heat a boiling tube of water to just above the temperature investigated (e.g 40 degrees)

- Add solute to water and stir rapidly until you get a saturated solution

- Allow solution to cool to exactly at 40 degrees

- Pour solution (careful not to pour any of the solid) into evaporating basin no need to pour all solution)

- Weigh evaporating basin with the contents

- heat the evaporating basin and contents gently to evaporate off all the water

- when it looks as if all the water has evaporated, wait, either breaking basin and contents

- Heat the evaporating basin and contents again and then re-weigh.

Why at the end, after weighing all the contents after water has evaporated, why do we re-weigh?

What is this called?

To make sure all the water has evaporated and is called heating to constant mass

Solubility curves (what do they show? How do we plot a solubility curve?)

Shows how the solubility of solids changes with temperature. Solubility graphs or curves represent solubility in g per 100 g of water plotted against temperature

To plot a solubility curve, the maximum mass of solute that can be dissolved in 100 g of water before a saturated solution is formed, is determined at a series of different temperatures.

Look at solubility curves + activities.

Because solubility varies with temperature, you must always quote a temperature with a solubility value, for example, the solubility of sodium chloride at 30°C is...

When we are performing the practical we are left with crystals. We say that the substance crystallises out of the solution or precipitates out of the solution

How can you calculate solubility in g per 100g of solvent?

Mass of solute

————————— x 100

Mass of solvent

If they give you 12g of solid is max mass it dissolves in 20g of water, then we multiply to make it 100g.

Solubility = 12 x 5/100= 60g/100g

1) Why did the value of the calculated solubility of the solid be smaller during the solubility practical? (1)

2) Suggest why the values for the solubility may be less accurate at 95 degrees than at lower temps (1)

3) Suggest why the boiling tube is not heated directly using a Bunsen burner (1)

Q 1 + 2)If the evaporating basin is heated too strongly some of the solid evaporates to form a gas. Therefore, some mass of water would be lost as the gas would be lost/evaporated/OWTTE

3) Water/solution might boil/evaporate

OR might spit out or be lost.

Suggest how the student could improve the reliability of her recorded temperature (1)

Repeat and find mean temperature

With what apparatus might be use to measure exactly 10cm^3of pure water? (1)

Pipette/burette

What safety precautions and protection should you use and why?

Eye protection (googles) and heat gently to avoid burns from hot solid spitting out of the basin

Suggest why the student's method (el de toda la vida) is not suitable for determining the solubility of hydrated copper(II) sulfate (1)

Any one from:

- hydrated copper(II) sulphate would become anhydrous copper sulphate

- hydrated copper sulphate would lose water

ALLOW the hydrated crystals would decompose